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Issued by the

Oil Companies International Marine Forum

First Published 1992

Second Edition 1997

Third Edition 2007

ISBN 1 85609 088 4

The Oil Companies International Marine Forum

(OCIMF) is a voluntary association of oil

companies having an interest in the shipment and terminalling of crude oil and oil products. OCIMF is
organised to represent its membership before, and to consult with, the International Maritime
Organization and other governmental bodies on matters relating to the shipment and terminalling of
crude oil and oil products, including marine pollution and safety.

British Library Cataloguing in Publication Data
Mooring Equipment Guidelines.

1. Oil Companies International Marine Forum
627.98
ISBN 1 85609 088 4

Terms of Use

The advice and information given in this guide ("Guide") is intended purely as guidance to be used at
the user's own risk. No warranties or representations are given nor is any duty of care or responsibility
accepted by the Oil Companies International Marine Forum (OCIMF), the membership or employees
of OCIMF or by any person, firm, corporation or organisation (who or which has been in any way
concerned with the furnishing of information or data, the compilation or any translation, publishing,
supply or sale of the Guide) for the accuracy of any information or advice given in the Guide or any
omission from the Guide or for any consequence whatsoever resulting directly or indirectly from
compliance with, adoption of or reliance on guidance contained in the Guide even if caused by a
failure to exercise reasonable care on the part of any of the aforementioned parties.

Printed & Published by

Witherby & Co. Ltd

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London EC1R OET, UK

Tel: +44 (0)20 7251 5341

Fax: +44 (0)207 7251 1296

iii

Introduction

The shipping industry has always been concerned with safe mooring practices. A fundamental
aspect of this concern entails the development of mooring systems which are adequate for the
intended service, with maximum integration of standards across the range of ship types and
sizes. To further this aim, the Oil Companies International Marine Forum first published
'Mooring Equipment Guidelines' in 1992 and this latest, third edition provides a major revision
and update to the original content to reflect changes in ship and terminal design, operating
practices and advances in technology.

Although numerous standards, guidelines and recommendations concerning mooring practices,
mooring fittings and mooring equipment exist, where guidance is given, it is often incomplete.
For example, the number of hawsers and their breaking strength may be recommended without
any advice on mooring winch pulling force or brake holding capacity. These guidelines are
intended to provide an extensive overview of the requirements for safe mooring from both a
ship and terminal perspective and embrace the full spectrum of issues from the calculation of a
ship's restraint requirements, the selection of rope and fitting types to the retirement criteria for
mooring lines.

A broad-based working group was established by OCIMF to develop the text for this edition
with membership from OCIMF members and from other industry associations that included the
International Association of Independent Tanker Owners (INTERTANKO), the International
Chamber of Shipping (ICS), the Society of International Gas Tanker and Terminal Operators
(SIGTTO), the International Association of Classification Societies (lACS), the International
Association of Ports and Harbors (IAPH), the Nautical Institute (NI) and the International
Harbour Masters Association (IHMA). Valuable contributions were also received from
representatives of rope manufacturers, winch manufacturers, equipment suppliers, shipyards
and specialist consultants.

The following is an overview of some of the substantive changes included in this edition:

Wind and current drag coefficients have been included from earlier OCIMF and
SIGTTO publications which are now out of print. All coefficient data is now appended to
the Guidelines.

The guidance has been expanded to account for site-specific conditions at terminals
and the impact on mooring patterns, additionally prompting consideration of the need
for more rigorous analysis incorporating vessel motion and dynamic force calculations.

Reference has been made to the content of IMO MSC/Circ.1175 "Guidance on
Shipboard Towing and Mooring Equipment" and related IACS Unified Requirement. . In
addition, guidance on ship's fittings associated with both emergency towing, escorting
and pull-back and harbour towing includes relevant content from the OCIMF publication
"Recommendations for Ships Fittings for Use with Tugs".

The concept of 'Design Basis Load' has been introduced for establishing the required
strength of ship's mooring fittings. The treatment of geometric effects such as wrap
angle on a fitting has been modified to align with practices in other industries and is no
longer automatically included within quoted safety factors.

It is recommended that all ship's mooring fittings should be designed to carry the MBL
of the attached mooring. The recommendations concerning the strength of ship's
mooring fittings are based on the principle of rope failure before fitting failure and fitting
failure before hull or foundation failure.

Recommendations on the marking of fittings are aligned with the requirements of IMO
MSC/1175, as adopted in SOLAS Chapter II – I, Regulation 3-8.

Full account has been taken of the introduction of new rope materials, such as those
manufactured from High Modulus Polyethylene (HMPE), and the related impact on
equipment design and operation. Relevant content from the OCIMF publication
"Guidelines on the Use of High-Modulus Synthetic Fibre Ropes as Mooring Lines on

Large Tankers" has been included.

Guidance on mooring line tails has been revised in the light of industry experience,
particularly with regard to their use at exposed berths.

Revised guidance is appended on the inspection and maintenance of mooring lines.

These guidelines represent best known mooring technology and practice. It is recognised that it
may not always be practical to retrofit all aspects of this technology to existing mooring
systems. For existing ships, where the mooring arrangement does not meet the
recommendations described in these guidelines, both ship and terminal operators should be
made aware of the limitations of the mooring system and contingency plans drawn up to deal
with them. The contingency plans should include (but not be limited to) predetermined
environmental limits for berthing, stoppage of cargo loading or unloading, and departure from
the berth.

Alternatives to the recommendations contained in these guidelines should only be introduced
on the basis of a formal risk assessment and should be implemented through a proper change
management process. The guidelines address 'conventional' mooring systems and
arrangements and novel designs, such as those employing vacuum pads, are not included. In
addition the guidelines are not intended to apply to vessels operating in extreme environments.

This publication attempts to refine, unify and update selected existing guidelines and to add
essential information which has either been omitted or poorly defined. Care has been taken to
ensure that design performance of equipment is optimised, while not overlooking the equally
important factors of ease of handling and safety of personnel.

These guidelines represent a recommended minimum requirement, and are intended to be
useful to ship and terminal designers and operators. They are not intended to inhibit innovation
or future technological advances. Although primarily addressing tankers and gas carriers, many
of the recommendations are considered to be equally applicable to other vessel types.

Contents

Section

Page

INTRODUCTION

LIST OF FIGURES

LIST OF TABLES

GLOSSARY OF TERMS AND ABBREVIATIONS

BIBLIOGRAPHY

PRINCIPLES OF MOORING

1.1

General

1.2

Forces Acting on the Ship

1.2.1

Wind and Current Forces

1.3

Mooring

Pattern

1.4

Elasticity

Lines

1.5

General Mooring Guidelines

1.6

Operational

Considerations

1.7

Terminal Mooring System Management

1.7.1

Operating

Limits

1.7.2

Operating

Guidelines/Mooring

Limits

1.7.3

Joint Terminal/Ship Meeting and Inspection

1.7.4

Instrumented

Mooring

Hooks

or Visual Inspection of Mooring

Lines

1.8

Ship Mooring Management

1.8.1

Line

Tending

1.9

Emergency and Excessively High Mooring Load Conditions

1.10

Limitations on Use of Tugs and Boats

1.11

General

Recommendations

1.11.1 Recommendations for Berth Designers

1.11.2 Recommendations for Terminal Operators

1.11.3 Recommendations for Ship Designers

1.11.4 Recommendations for Ship Operators

MOORING RESTRAINT AND ENVIRONMENTAL CRITERIA

2.1 General

Considerations

2.2

Standard Environmental Criteria

2.3

Calculation of Forces

2.4

Mooring Restraint Requirements

2.4.1

Basic Principles of Mooring Calculations

2.4.1.1

The

Principle

of Static Equilibrium

Section

Page

2.4.1.2

The

Load/Deflection

Characteristics of each Mooring

Line

and

Breasting

Dolphin

2.4.1.3

The

Geometrical

Relationship Between the Parts of

the

System

2.4.2

Standard Restraint Requirements

2.5

Site-Specific Environmental Data and Mooring Line Loads

2.5.1

Most Probable Maximum (MPM) Loads

MOORING ARRANGEMENTS AND LAYOUTS

3.1

Principal

Objectives

3.2

Requirements at Piers and Sea Islands

3.2.1

Number, Size and Type of Lines

3.2.2

Arrangements for Breast Lines

3.2.3

Arrangements for Spring Lines

3.2.4

Special Arrangements for Gas Carriers

3.3

Requirements at SPMs

3.4

Requirements for Emergency Towing, Escorting and Pull-Back

3.4.1

Fittings for Tug Escort and Pull-Back

3.5

Requirements for Multi-Buoy Moorings

3.6

Requirements for Harbour Towing

3.7

Requirements for Barge Mooring

3.8

Requirements for Canal Transit

3.9

Requirements for Ship-to-Ship (STS) Transfer

3.9.1

Requirements for Offtaker

3.9.2

Requirements for Discharge Ship

3.10

Arrangements at Cargo Manifolds

3.11

Mooring Augmentation in Exceptional Conditions

3.11.1 Provision of Shore Moorings

3.11.2 Use of Shore-Based Pulley

3.11.3 Advantage of Pulley System

3.11.4

Disadvantage

of Pulley System

3.12

Emergency Towing-off Pennants

3.13

Combination of Various Requirements

3.14

Safety and Operational Considerations

3.15

Equipment and Fitting Line-up

DESIGN LOADS, SAFETY FACTORS AND STRENGTH

4.1

General

4.2

Basic

Strength

Philosophy

4.3

Existing Standards and Requirements

4.4

Recommended Design Criteria

4.4.1

Bitts (Double Bollards)

4.4.2

Single Cruciform Bollard

vii

Section

Page

4.4.3

Recessed

Bitt

4.4.4

Closed

Chocks

4.4.5

Pedestal fairleads and Rollers of Button-Roller Chocks

4.4.6

Universal Fairlead (4 Roller Type)

4.4.7

Universal Fairlead (5 Roller Type)

4.4.8

Emergency Towing Arrangement

4.4.9

Single Point Mooring Equipment

4.4.10 Mooring

Winches

4.4.11 Comparison of Combined Stresses with the 85% of Yield Criterion

4.5

Strength

Testing

of Mooring Fittings

4.6

Marking of Mooring Fittings

4.7

General

Recommendations

4.7.1

Recommendations for Ship Designers

4.7.2

Recommendations for Ship Operators

5 STRUCTURAL

REINFORCEMENTS

5.1

Basic

Considerations

5.2

Mooring

Winches

5.3

Chocks and Fairleads

5.4

Pedestal

Fairleads

5.5

Bitts

5.6

Recessed

Bitts

5.7

SPM Fittings and Smit Brackets

5.8

Tug Push Points

5.9

Special

Considerations

5.9.1

Rounded Gunwhale Connection

5.9.2

Doublers Versus Inserts

5.9.3

High Strength Steel Fittings

5.10

Certification and Inspection

MOORING LINES

6.1

General

6.1.1

General Safety Hazards

6.1.2

Strength

Criteria

6.1.3

Record

Keeping

6.2

Wire Mooring Lines

6.2.1

Material

6.2.2

Construction

6.2.3

Corrosion

Protection

6.2.4

Bend

Radius

6.2.5

Handling, Inspection and Removal from Service

6.2.6

Standard

Specifications

6.3

Conventional Fibre Mooring Lines

6.3.1

General

viii

Section

Page

6.3.1.1

Polyester

6.3.1.2 Polyamide (previously referred to as 'Nylon')

6.3.1.3

Polypropylene

6.3.1.4

Combinations

Materials

6.3.2

Construction

6.3.3

Bend

Radius

6.3.4

Handling

and

Storage of Synthetic Lines

6.4

High Modulus Fibre Mooring Lines

6.4.1

General

6.4.2

Properties of High Modulus Synthetic Fibres

6.4.3

High Modulus Synthetic Fibre Materials

6.4.3.1

Trade

Names

6.4.3.2

Aramid

Fibres

6.4.3.3 Liquid Crystal Polymer (LCP) Fibres

6.4.3.4 High Modulus Polyethylene (HMPE) Fibres

6.4.4

High Modulus Synthetic Rope Constructions

6.4.5

Characteristics

6.4.5.1

Strength

6.4.5.2

Elasticity

6.4.5.3

Chemical

Resistance

6.4.6

Selection

Criteria

6.4.6.1

Strength

6.4.6.2

Construction

6.4.6.3

Elastic

Elongation

6.4.6.4

Coefficient

Friction

6.4.7

Installation

6.4.7.1

General

6.4.7.2

Chafe

Protection

6.4.7.3

Mooring

Winches

6.4.7.4 Fatigue and Service Life

6.4.8

Inspection and Removal from Service

6.5

Synthetic

Tails

6.5.1

General

6.5.2

Tail

Length

6.5.3

Retirement

Criteria

6.5.4

Methods of Connecting Tails

WINCH PERFORMANCE, BRAKE HOLDING CAPACITY AND STRENGTH
REQUIREMENTS

7.1

Function and Type of Mooring Winches

7.1.1

Automatic Tension Winches

7.2

Winch Drums

7.2.1

Split

Drums

7.2.2

Undivided

Drums

Section

Page

7.2.3

Handling of SPM Pick-up Ropes

7.3

Winch

Drives

7.3.1

Hydraulic

Drives

7.3.2

Self-Contained Electro-Hydraulic Drives

7.3.3

Electric

Drives

7.3.4

Steam

7.4

Winch

Brakes

7.4.1

Layers of Mooring Line on Drum

7.4.2

Band

Brakes

7.4.2.1

Torque

Applied

7.4.2.2

Condition of the Winch

7.4.2.3

Winch

Gear

7.4.2.4

Friction

Coefficient

7.4.2.5

Load

Dependency

Holding

Capacity

7.4.2.6 Sensitivity in Reeling Direction

7.4.3

Disc Brakes

7.4.4

Input

Brakes

7.4.5

Winch Brake Testing

7.4.5.1

General

7.4.5.2

Frequency

7.4.5.3

Test

Specification

7.4.5.4

Supervision

Testing

7.4.5.5

Test

Equipment

7.4.5.6

Method

Testing

7.4.6

Brake

Holding

Capacity

7.5

Winch

Performance

7.5.1

Rated

Pull

7.5.2

Rated

Speed

7.5.3

Light-Line Speed

7.5.4

Stall Heaving Capacity

7.5.5

Drum

Capacity

7.6

Strength

Requirements

7.7

Winch

Testing

7.7.1

Rules Concerning Testing at Manufacturer's Facility for the

Acceptance of the Manufacturer and Purchaser

7.7.2

On-board Acceptance Tests and Inspections

7.8

Summary

Recommendations

7.8.1

Recommendations for Ship Designers

7.8.2

Recommendations for Ship Operators

MOORING FITTINGS

8.1

Introduction

8.2

Mooring

Bitts

8.3

Cruciform

Bollards

Section

Page

8.4

Closed and Panama-Type Chocks

8.5

Roller Fairleads and Pedestal Fairleads

8.6

Universal Roller Fairleads

8.7

Stoppers

8.8

Selection of Fitting Type

APPENDICES

Wind and Current Drag Coefficients for VLCC's and Gas Carriers and Example
Force Calculation

Rope Over-strength

Guidelines for Handling, Inspection and Removal from Service of Wire Mooring
Lines

Guidelines for Inspection and Removal from Service of Fibre Ropes

Tanker Mounted SPM Fittings

Strength of Chain Tensioned over a Curved Surface

INDEX

List of Figures

Figure

Page

1.1

Typical Mooring Pattern

1.2

Wind Forces on a Ship

1.3

Effect of Underkeel Clearance on Current Force

1.4

Mooring Pattern Analysis

1.5

Effect of Hawser Orientation on Restraint Capacity

1.6

Effect of Mooring Elasticity on Restraint Capacity

1.7

Comparison of Steel Wires Versus HMPE Mooring Lines with and without 11m Tails

1.8

Effect of Line Length on Tending Requirements

2.1

Generic Mooring Layout Used for Computational Purposes

3.1

Typical Mooring Arrangement of a Tanker

3.2

Tanker - Mooring Arrangement on the Forward Deck

3.3

Tanker - Mooring Arrangement on the Aft Deck

3.4

Special Arrangement for Aft Back Springs

3.5

Typical Mooring Arrangment of an LNG Carrier

3.6

LNG Carrier - Mooring Arrangement on the Forward Deck

3.7

LNG Carrier - Mooring Arrangement on the Aft Deck

3.8

Typical Emergency Towing Arrangement at Forward End

3.9

Typical Emergency Towing Arrangement at Aft End

3.10

Multi-Buoy Mooring (MBM)

3.11

Mooring Pattern During Ship-to-Ship Transfer

3.12

Rigging of Emergency Towing-off Pennant

3.13

Alignment and Maximum Fleet Angle for Mooring Winches

5.1

Typical Cantilevered Foundation in Way of Mid-Body Area

5.2

Installation Example of Universal Fairlead with Doublers in way of Rounded Gunwhale

5.3

Roller Fairlead with Individual End Frames

5.4

Deck Reactions with Two Types of Universal Fairleads

5.5

Typical Foundation for Pedestal Fairlead

5.6

Deck Reinforcement for Pedestal Fairlead

5.7

Extended Reinforcement Example to Reduce Stress on Longitudinals

6.1

Examples of Potential Snap-Back Danger Zones

6.2

Wire Line Constructions

6.3

Effects of Bending on Wire Rope Strength

6.4

Construction of Conventional and High Modulus Synthetic Fibre Ropes

6.5

Load - Extension Characteristics - Wire and Fibre Ropes, New and Broken-In

6.6

Fairing of Split Drum Edge

B) & C) Faired Split Drum Edge

6.7

Typical Links for Connecting Lines with Tails

6.8 Cow

Hitch

7.1

The Split Drum Winch

7.2

Jacketed High Modulus Fibre Moorings on Split Drum Winches

7.3

Calculation of Mooring Line MBL and Relationship to Winch Parameters

7.4

Effect of Applied Torque on Brake Holding Power

7.5

Spring-Applied Brake with Hydraulic Release

7.6

Spring-Applied Brake with Manual Setting and Release

7.7

Improper Fitting of Locking Nuts to Brake Tightening Screw

7.8

Typical Winch Brake Test Equipment

7.9

Simplified Brake Test Kit

7.10

Effect of Slippage on Final Brake Holding Load – Spring-Applied Brakes

xii

Figure

Page

8.1

Methods of Belaying a Rope on Bitts

8.2 Closed

Chock

8.3

Types of Universal Roller Fairleads

8.4

Additional Chafe Plates for Type A Fairleads

8.5

Universal Fairleads with Additional Inboard Rollers

8.6 Stoppers

Sign Convention and Co-ordinate System

Longitudinal Wind Drag Force Coefficient

Lateral Wind Drag Force Coefficient

Wind Yaw Moment Coefficient

Longitudinal Current Drag Force Coefficient – Loaded Tanker (WD/T = 1.1)

Longitudinal Current Drag Force Coefficient – Loaded Tanker (WD/T = 1.2)

Longitudinal Current Drag Force Coefficient – Loaded Tanker (WD/T = 1.5)

Longitudinal Current Drag Force Coefficient – Loaded Tanker (WD/T = 3.0)

Longitudinal Current Drag Force Coefficient – Loaded Tanker (WD/T > 4.4)

A10

Lateral Current Drag Force Coefficient – Loaded Tanker

A11

Current Yaw Moment Coefficient – Loaded tanker

A12

Longitudinal Current Drag Force Coefficient – Ballasted Tanker (40% T)

A13

Lateral Current Drag Force Coefficient – Ballasted Tanker (40% T)

A14

Current Yaw Moment Coefficient – Ballasted Tanker (40% T, Based on Midships)

A15

Variation in Bow Configuration

A16

Current Velocity Correction Factor

A17

Longitudinal Wind Drag Force Coefficient – Gas Carrier

A18

Lateral Wind Drag Force Coefficient – Gas Carrier

A19

Wind Yaw Moment Coefficient – Gas Carrier

Depiction of HMPE Mooring Line Residual Strength

Proper Method of Locating Rope Anchorage Point on a Plain Drum

Examples of Rope Damage with Broken Wires

Reduction in Wire Rope Diameter

Wire Rope Crushing Damage

Rope Stretch Leading to Decreased Elasticity

Cross Section Depicting Substantial Wear and Severe Lateral Corrosion

Basket or Lantern Deformation

An Open Kink and Examples of Damage Caused

D1 New

Rope

Used Rope

D3 Damaged

Rope

Residual Strength to Rope Damage Relationships

D5 Surface

Abrasion

Plucked Strand in Cover

Single Cut Strand

Multiple Cut Strands

Glazed, No Fibre Damage (Bent Rope)

D10

Glazed, No Fibre Damage (Flat rope)

D11

Same Rope as Figures C9 and C10: After Flexing No Permanent Damage

D12 Actual

Melting

Damage

Typical Tongue-Type Bow Chain Stopper

Positioning of Forward Fairleads, Bow Chain Stoppers and Pedestal Roller Leads

Three Cases of a Chain Bent over a Curved Surface

Geometry of a Chain Bent over a Curved Surface

Approximate Relation Between Angle α and Angle ß

xiv

List of Tables

Table

Page

1.1

Maximum Longitudinal and Transverse Wind Forces on a 250,000 DWT Tanker

1.2

Tanker 107,000 DWT, 35 knot Wind 135º and 225º; 5 knot Current 170º; and 2 metre, 10
second 225º Swell

1.3 LNG

Carrier

267,000m

, 35 knot Wind 135º and 225º; 5 knot Current 170º; and 2 metre, 10

second 225º Swell

3.1

Emergency Towing-off Pennants – Recommended MBL and Length

4.1

Comparison Between Section 4.4 and MSC Circ 1175

5.1

Typical Pad Width and Thickness

6.1 Strength

Criteria

6.2

Typical MBLs of Steel Wire Rope

6.3

Typical Characteristics of Materials used for Conventional Synthetic Ropes

6.4

Minimum Breaking Forces in kN of Synthetic Ropes (New, Dry Ropes, Unspliced)

6.5

Typical Properties of High Modulus Synthetic Fibres and Steel Wire Ropes

6.6

Examples of High Modulus Synthetic Fibre Trade Names

6.7

Typical MBLs of High Modulus Synthetic Fibre Ropes

7.1 Performance

Specification for Mooring Winches

8.1

Maximum Permissible Rope Loading of Bitts

A.1 Principal

Dimensions/Characteristics of Typical Liquefied Gas Carriers

C.1

Summary of the Major Criteria for the Inspection and Discard of Wire Ropes

F.1

Chain Tensioned over Curved Surface, Properties of Chain Samples

F.2

Summary of Test Results, Chain Tensioned over Curved Surface

Glossary of Terms and Abbreviations

ABRASION
RESISTANCE

The ability of a fibre or rope to withstand surface wear and
rubbing due to motion against other fibres of rope components
(internal abrasion) or a contact surface such as a fairlead
(external abrasion).

ARAMID

A manufactured fibre consisting of very long molecular chains
formed by rearranging the structure of aromatic polyamides.

AXIAL
COMPRESSION
FATIGUE

The tendency of a fibre to fail when it is subjected to cyclic
loading, which exerts compression along its axis.

BIGHT

A loop formed by doubling back a rope upon itself.

BITTS

Vertical steel posts or bollards mounted in pairs around which a
line can be secured.

BOLLARD

A vertical post ashore to which the eye of a mooring line can be
attached.

BOSS SHACKLE

A special shackle used to connect a wire mooring line to a
synthetic tail.

BOW CHAIN STOPPER

A mechanical device for securing chafe chains on board a
tanker.

BRAIDED ROPE

A rope produced by intertwining a number of strands.

BREAKING STRENGTH

For cordage, the nominal force (or load) that would be expected
to break or rupture a single specimen in a tensile test conducted
under a specified procedure. On a group of like specimens it
may be expressed as an average or as a minimum based on
statistical analysis.

BREAST LINES

Mooring lines leading ashore as nearly perpendicular as
possible to the ship's fore and aft line.

CARPENTER'S
STOPPER

A carpenter's stopper is a device with opening jaws to receive
wire and shaped wedges to hold line when tension is applied.

CHAFE CHAIN

A length of stud link chain, at the end of an SPM mooring
hawser, which passes through a ship's fairlead, and is used to
connect the SPM mooring hawser to the bow chain stopper of
the tanker.

CHOCK

A guide for a mooring line which enables the line to be passed
through a ship's bulwark or other barrier (See also FAIRLEAD).

COEFFICIENT OF
FRICTION

The limiting value of the coefficient given by dividing the force
tending to cause one body to slide over another by the normal
force between the two bodies. Generally, the higher the value,
the lower the tendency of one object to slide over another.

CONVENTIONAL BUOY
MOORING (CBM)

See Multi-Buoy Mooring

xvi

CRITICAL
TEMPERATURE

The temperature at which the properties of a fibre begin to
deteriorate.

DEADWEIGHT(DWT)

The carrying capacity of a ship, including cargo, bunkers and
stores, in metric tonnes. It can be given for any draft, but here it
is used to indicate summer deadweight at summer draft.

DESIGN BASIS LOAD

The design load on a fitting, given by multiplying the mooring
Minimum Breaking Load (MBL) by the Geometric Factor (GF).

DIRECTIONAL
ENVIRONMENT

A location where a single direction for environmental forces
dominates.

DISPLACEMENT

The mass of water in tonnes displaced by a vessel at a given
draft.

DOLPHIN

An independent platform incorporating mooring hooks or
bollards for securing ship's mooring lines.

ELASTIC ELONGATION

The temporary change in length of a fibre or yarn under tension,
which is revered when the tension is removed.

ELASTICITY

The elastic (non permanent) elongation of a unit length of an
element caused by a unit load. May refer to a material or a
composite structure such as a mooring line.

ELONGATION

Refers here to the total extension (elastic and plastic) of a line.

EMERGENCY TOWING-
OFF PENNANT

A line rigged to the waterline over the off-berth side of a ship to
facilitate towing off in an emergency.

FAIRLEAD

A guide for a mooring line which enables the line to be passed
through a ship's bulwark or other barrier, or to change direction
through a congested area without snagging or fouling.

FATIGUE

The tendency of a material to weaken or fail during alternate
tension-tension or tension-compression cycles. In cordage,
particularly at loads well below the breaking strength, this
degradation is often caused by internal abrasion of the fibres
and yarns but may also be caused by fibre damage due to
compression. Some fibres develop cracks or splits that cause
failure, especially at relatively high loads.

FIBRE

A long, fine, very flexible structure that may be woven, braided,
stranded or twisted into a variety of fabrics, twine, cordage or
rope.

FIRST-LINE ASHORE

A line (usually fibre) put ashore first to help in hauling the ship
into berth.

FLEET ANGLE

The angle between the mooring line and a plane perpendicular
to the axis of the winch drum or, for split drums, the tension
section of the drum.

FPSO

Floating Production, Storage and Offloading Unit.

FSO

Floating Storage and Offloading unit.

GEOMETRIC FACTOR

The factor by which the line tension is multiplied to take account
of the angle through which a line is deflected around a fitting.

HAWSER

Synthetic or natural fibre rope or wire rope used for mooring,
warping and towing

xvii

warping and towing.

HEAD LINES

Mooring lines leading ashore from the fore end of a ship, often
at an angle of about 45 degrees to the fore and aft line.

HEAVING LINE

A very light line that is thrown between the ship and the berth,
and is used to draw a messenger line ashore.

HIGH MODULUS
POLYETHYLENE
(HMPE)

A manufactured fibre based on Ultra High Molecular Weight
Polyethylene (UHMWPE).

HTS

High Tensile Steel.

IMO

International Maritime Organization

INDEPENDENT WIRE
ROPE CORE (IWRC)

A type of construction of wire rope.

ISO

International Organization for Standardization.

LEAD

The direction a mooring line takes up whilst being handled or
when made fast.

LENGTH BETWEEN
PERPENDICULARS (LBP)

The length of a ship, generally between the stem at the design
loadline and the centre of the rudder stock.

LENGTH OVERALL (LOA) The extreme length of a ship

LOADING ARMS

Transfer units between ship and shore for discharge and
loading; may be articulated all-metal arms (hard arms) or a
combination of metal arms and hoses.

MANDAL SHACKLE

A special shackle used to connect a wire mooring line to a
synthetic tail.

MARPOL

International Convention for the Prevention of Pollution from
Ships, 1973 as modified by the Protocol of 1978.

MARPOL TANKER

IMO Categories 2 and 3 oil tankers. A Category 2 tanker is one
of 20,000 tonnes deadweight and above carrying crude oil, fuel
oil, heavy diesel oil or lubricating oil, or of 30,000 tonnes
deadweight and above carrying other oils which complies with
MARPOL requirements for protectively located segregated
ballast tank arrangements. A Category 3 tanker is one of 5,000
tonnes deadweight and above, but less than the tonnage
specified for Category 2 tankers.

MESSENGER LINES

A light line attached to the end of a main mooring line and used
to assist in heaving the mooring to the shore or to another ship.

MINIMUM BREAKING
LOAD (MBL)

The minimum breaking load of a new dry mooring line or chain
as declared by the manufacturer.

MOORING RESTRAINT

The capability of a mooring system to resist external forces on
the ship.

MULTI-BUOY
MOORINGS (MBM)

A facility whereby a tanker is usually moored by a combination
of the ship's anchors forward and mooring buoys aft and held on
a fixed heading. Also called conventional buoy moorings (CBM).

MULTI-DIRECTIONAL
ENVIRONMENT

A location where no single direction for environmental forces
dominates or where none of the forces becomes a dominant

xviii

ENVIRONMENT

factor.

NEWTON (N)

A unit of force. 1kN = 1000 N.

PANAMA TYPE
FAIRLEAD

A non-roller type fairlead mounted at the ship's side and
enclosed so that mooring lines may be led to shore with equal
facility either above or below the horizontal. Strictly pertains only
to fairleads complying with Panama Canal Regulations, but
often applied to any closed fairlead or chock.

PEDESTAL ROLLER
FAIRLEAD

A roller fairlead usually operating in a horizontal plane. Its
purpose is to change the direction of lead of a mooring or other
line on a ship's deck.

PLAITED ROPE

A rope structure consisting of two pairs of strands twisted to the
right and two pairs of strands twisted to the left and braided
together such that pairs of strands of opposite twist alternatively
overlay one-on-another.

PRE-MARPOL TANKER

An IMO Category 1 oil tanker of 20,000 tonnes deadweight and
above carrying crude oil, fuel oil, heavy diesel oil or lubricating
oil or of 30,000 tonnes deadweight and above carrying other
oils, which does not comply with the requirements for
protectively located ballast tanks.

PRE-TENSION

Additional load applied to a mooring line by a powered winch
over and above that required to remove sag from the main run
of the line.

SAFETY FACTOR

A margin over MBL to allow for uncertainties.

SAFE WORKING LOAD
(SWL)

Generally, a load less than the yield or failure load by a safety
factor defined by a code, standard or good engineering practice.

In these guidelines, the SWL of a fitting is greater than or equal
to the Minimum Breaking Load of the mooring that contacts the
fitting, while the SWL of a mooring line itself is defined more
conventionally.

SEA ISLAND

A pier structure with no direct connection to the shore, at which
tankers can berth.

SEICHE

Very long waves of small height generated by resonant
oscillation within a partly closed harbour or other body of water.
Strong horizontal currents can also be set up which may cause
ship surging in adverse circumstances.

SHIP-TO-SHIP
TRANSFER
OPERATIONS (STS)

Transfer of liquid cargo between two ocean-going ships made
fast alongside at anchor or underway. The transfer of
petroleum to barges and estuarial craft, including bunkering
operations, is specifically excluded.

SINGLE POINT
MOORING (SPM)

An integrated mooring arrangement for bow mooring a
conventional tanker. For example, conventional tanker bow
mooring arrangements to Catenary Anchor Leg Mooring
(CALM) system, Single Anchor Leg Mooring (SALM) system,
FPSO or FSO.

SMIT BRACKET

A fitting for securing the end link of a chafing chain, consisting
of two parallel vertical plates mounted on a base with a sliding
bolt passing through the plates.

xix

SOLAS

The International Convention for the Safety of Life at Sea,
1974 and 1988 Protocol, as amended.

SPECIFIC GRAVITY

The ratio of the mass of a material to the mass of an equal
volume of fresh water.

SPECIFIED MINIMUM
YIELD STRESS (SMYS)

The yield stress of steel as specified by the purchaser and
guaranteed as a lower bound to the actual yield stress by the
supplier.

SPRING LINES

Mooring lines leading in a nearly fore and aft direction, the
purpose of which are to maintain the longitudinal position of
the ship while in berth. Headsprings prevent forward motion
and backsprings aft motion.

STERN LINES

Mooring lines leading ashore from the after end or poop of a
ship, often at an angle of about 45 degrees to the fore and aft
line.

STOPPER

A device for securing a mooring line temporarily at the ship
whilst the free end is made fast to a ship's bitt.

STRAND

The largest individual element used in the final rope-making
process and obtained by joining and twisting or braiding
together several yarns or groups of yarns.

SUMMER
DEADWEIGHT

The deadweight of a ship when loaded to summer marks.

TAIL

A short length of synthetic rope attached to the end of a
mooring line to provide increased elasticity and also ease of
handling. Also referred to as 'pennant' or 'pendant'.

TONNE (t)

Metric tonne equal to 1,000 kilograms. A unit of mass that is
often also used for forces (sometimes expressed as ‘tf’); 1tf =
9.81kN.

TONSBERG SHACKLE

A special shackle used to connect a wire mooring line to a
synthetic tail.

ULTRA LARGE CRUDE
CARRIER (ULCC)

Tankers able to transport up to 3 million barrels of oil as cargo,
typically above 320,000 tonnes deadweight.

UNIVERSAL FAIRLEAD

A fairlead with three or more cylindrical rollers.

UTS

Ultimate tensile strength.

VERY LARGE CRUDE
CARRIER (VLCC)

Tankers able to transport up to 2 million barrels of oil as cargo,
typically of between 200,000 and 320,000 tonnes deadweight.

YARN

A generic term for a continuous strand of textile fibres,
filaments or material in a form suitable for intertwining to form
a textile structure via any one of a number of textile processes.

Bibliography

Reference 1

OCIMF publication "Recommendations for Equipment Employed in the Bow

Mooring of Conventional Tankers at Single Point Moorings".

Reference 2

OCIMF publication "Recommendations for Oil Tanker Manifolds and

Associated Equipment".

Reference 3

OCIMF/ICS publication "Ship to Ship Transfer Guide (Petroleum)".

Reference 4

OCIMF/ICS/IAPH publication "International Safety Guide for Oil Tankers and

Terminals".

Reference 5

IMO MSC/Circ.1175 "Guidance on Shipboard Towing and Mooring
Equipment", 24

May 2005.

Reference 6

IACS UR A2 "Shipboard Fittings and Associated Hull Structures Associated
with Towing and Mooring on Conventional Vessels".

Reference 7

OCIMF publication "Guidelines for the Purchasing and Testing of SPM

Hawsers".

Reference 8

Marsh, F.W. and Thurston, R.C.A., "Investigation of Stress Distribution in

Stud Link Anchor Cable", Report IR61-46, Department of Mines and

Technical Surveys, Ottawa, Canada.

Reference 9

Buckle, A. K., "Anchoring and Mooring Equipment on Ships", 1974, Royal

Institute of Naval Architects.

Reference 10

OCIMF Hawser Test Report, 1982

Reference 11

Optimoor User's Guide, Tension Technology International

Reference 12

Joint Industry Project, Develop Effective Moorings for Tanker and Gas
Carrier Terminals Exposed to Waves, final report Mooring Analyses & Safe
Mooring Practices for Exposed Terminals, rev 1 dated 17/11/2006.

Reference 13

Design Manual, “Harbor and Coastal Facilities”, NAVDOCKS DM-26, Bureau
of Yards and Docks, Department of the Navy.

In addition, the following out-of-print documents have been referenced:

OCIMF

Prediction of Wind and Current Loads on VLCC’s 2

Edition 1994.

OCIMF/SIGGTO

Prediction of Wind Loads on Large Liquefied Gas Carriers, 1995.

Section 1

Principles of Mooring

1.1 GENERAL

The term "mooring" refers to the system for securing a ship to a terminal. The most common
terminals for tankers are piers and sea islands. However, other shipboard operations such as
mooring at Single Point Moorings (SPM's), Multi-Buoy Moorings (MBM's), Floating Production,
Storage and Offloading vessels (FPSO’s) and offshore loading facilities, emergency towing, tug
handling, barge mooring, canal transit, ship-to-ship transfer and anchoring may fall into the broad
category of mooring and thus require specialised fittings or equipment. Anchoring equipment is
covered by Classification Society rules and is therefore not included in these guidelines.

Figure 1.1 shows a typical mooring pattern at a tanker terminal.

FIGURE 1.1: TYPICAL MOORING PATTERN

The use of an efficient mooring system is essential for the safety of the ship, her crew, the
terminal and the environment. The problem of how to optimise the moorings to resist the various
forces will be dealt with by answering the following questions:

• What are the forces applied on the ship?

• What general principles determine how the applied forces are distributed to the mooring

lines?

• How can the above principles be applied in establishing a good mooring arrangement?

Since no mooring arrangement has unlimited capability, in order to address these questions it will
be necessary to understand precisely what the moorings of a ship are expected to achieve.

Section 1

1.2 FORCES ACTING ON THE SHIP

The moorings of a ship must resist the forces due to some, or possibly all, of the following
factors:

•  Wind
•  Current
•  Tides
•  Surges from passing ships
•  Waves/Swell/Seiche
•  Ice
•  Changes in draft, trim or list

This Section deals mainly with the development of a mooring system to resist wind, current and
tidal forces on a ship at a conventional berth. Normally, if the mooring arrangement is designed
to accommodate maximum wind and current forces, reserve strength will be sufficient to resist
other moderate forces which may arise. However, if appreciable surge, waves or ice conditions
exist at a terminal, considerable loads can be developed in the ship's moorings. These forces
are difficult to analyse except through model testing, field measurements or dynamic computer
programs. Ships calling at such terminals should be made aware that the standard
environmental condition may be exceeded and appropriate measures will need to be
implemented in advance.

Forces in the moorings due to changes in ship elevation from either tidal fluctuations or loading
or discharging operations must be compensated by proper line tending.

1.2.1

Wind and Current Drag Forces

The procedures for calculating these forces are covered in Section 2 of these guidelines and in
Appendix A. Although the initial calculations were based on large ships, additional testing
conducted for smaller ships has shown that the wind and current drag coefficients are not
significantly different for most cases. Consequently, the large ship coefficients in Appendix A
may be used for bridge-aft ships with similar geometry down to 16,000 DWT in size.

Figure 1.2 demonstrates how the resultant wind force on a ship varies with wind velocity and
direction. For simplicity, wind forces on a ship can be broken down into two components: a
longitudinal force acting parallel to the longitudinal axis of the ship, and a transverse force acting
perpendicular to the longitudinal axis. The resultant force initiates a yawing moment.

Wind force on the ship also varies with the exposed area of the ship. Since a head wind only
strikes a small portion of the total exposed area of the ship, the longitudinal force is relatively
small. A beam wind, on the other hand, exerts a very large transverse force on the exposed side
area of the ship. For a given wind velocity the maximum transverse wind force on a VLCC is
about five times as great as the maximum longitudinal wind force. For a 50-knot wind on a light
250,000 DWT tanker, the maximum transverse forces are about 320 tonnes (3138 kN), whereas
the ahead longitudinal forces are about 60 tonnes (588 kN).

Mean Draft

metres

Astern

tonnes

Ahead

tonnes

Transverse

tonnes

6 47.8 68 303

7 47.2

66.7

283

8 46.7

65.3

263

9 46.1

63.9

244

TABLE 1.1: MAXIMUM LONGITUDINAL AND TRANSVERSE WIND FORCES ON A 250k

DWT TANKER, 5m TRIM, 50 knot WIND

Section 1

FIGURE 1.3: EFFECT OF UNDERKEEL CLEARANCE ON CURRENT FORCE

Assumes 2 knot current, 5º off the bow

[data in Figure to change to 12 t (118 kN); 25 t (245 kN); 40 t (392 kN) and 70 t (686 kN)]

Current forces on the ship must be added to the wind forces when evaluating a mooring
arrangement. In general, the variability of current forces on a ship due to current velocity and
direction follows a pattern similar to that for wind forces. Current forces are further complicated by
the significant effect of clearance beneath the keel. Figure 1.3 shows the increase in force due to
reduced underkeel clearance. The majority of terminals are oriented more or less parallel to the
current, thereby minimising current forces. Nevertheless, even a current with a small angle (such
as 5°) off the ship's longitudinal axis can create a large transverse force and must be taken into
consideration.

Model tests indicate that the current force created by a one knot head current on a loaded
250,000 DWT tanker with a two metre underkeel clearance is about 5 tonnes (49 kN), whereas
the load developed by a one-knot beam current for the same underkeel clearance is about 230
tonnes (2268 kN). For a two knot current, the force created would be about 14 tonnes (137 kN)
when from ahead and 990 tonnes (9,708 kN) when on the beam.

1.3 MOORING PATTERN

The term 'mooring pattern' refers to the geometric arrangement of mooring lines between the
ship and the berth. It should be noted that the industry has previously standardised on the
concept of a generic mooring layout (see Figure 2.1), taking into account standard
environmental criteria. The generic mooring layout is mainly applicable to a 'multi-directional'
environment and for the design of ship’s mooring equipment. 'Multi-directional' is where no
single direction dominates or any of the environmental forces becomes a dominant factor.

For terminals with a 'directional environment', for example a high current, wind or swell waves, a
site-specific layout such as one including head and stern lines and/or extra breast and spring
lines may be more efficient. For ships regularly trading to these terminals, consideration may be
given to the provision of additional or higher capacity mooring equipment.

The most efficient line 'lead' for resisting any given environmental load is a line orientated in the
same direction as the load. This would imply that, theoretically, mooring lines should all be
oriented in the direction of the environmental forces and be attached at such a longitudinal
location on the ship that the resultant load and restraint act through one and the same location.

Section 1

Such a system would be impractical since it has no flexibility to accommodate the different
environmental load directions and mooring point locations encountered at various terminals. For
general applications, the mooring pattern must be able to cope with environmental forces from
any direction. This can best be approached by splitting these forces into a longitudinal and a
transverse component, and then calculating how to most effectively resist them. It follows that
some lines should be in a longitudinal direction (spring lines) and some lines in a transverse
direction (breast lines). This is the guiding principle for an effective mooring pattern for general
application, although locations of the actual fittings at the terminal will not always allow it to be
put into practice. The decrease in efficiency by deviating from the optimum line lead is shown in
Figs. 1.4. and 1.5 (Compare Cases 1 and 3 in Fig 1.4 where the maximum line load increases
from 57 (559 kN) to 88 tonnes (863 kN)).

However, it should be noted that for a 60 knot head wind the highest loaded line for the generic
layout is 39.5 tonnes, whereas it is 28.6 tonnes for the specific layout. Hence, for terminals
located where the environment is directional, the specific layout is actually more efficient. Refer
to Sections 1.5, 1.6, 1.7, 2.4 and 2.5 for further details.

There is a basic difference in the function of spring and breast lines which must be understood
by designers and operators alike. Spring lines restrain the ship in two directions (forward and
aft); breast lines essentially deployed perpendicular to the ship restrain in only one direction (off
the berth), restraint in the on-berth direction being provided by the fenders and breasting
dolphins. Whereas all breast lines will be stressed under an off-berth environmental force, only
the aft or the forward spring lines will generally be stressed. For this reason the method of line-
tending differs between spring and breast lines (as explained in Section 1.8.1). It is important to
recognise that if spring lines are pre-tensioned, the effective longitudinal restraint is provided by
only the difference between the tension in the opposing spring lines. Hence, too high a pre-
tension can significantly reduce the efficiency of the mooring system. Likewise, differences in
vertical angles between forward and aft springs can lead to ship surge along the jetty.

Mooring patterns for a directional environment may incorporate head and stern lines which are
orientated between a longitudinal and transverse direction. This then optimises restraint for the
longitudinal direction where the dominant environmental force acts, whilst maintaining some
lateral restraint for the less dominant lateral environmental directions.

Another option for mooring layouts with dominant longitudinal forces is to add more spring lines.

Furthermore, the effectiveness of a mooring line is influenced by two angles: the vertical angle
the line forms with the pier deck and the horizontal angle the line forms with the parallel side of
the ship. The steeper the orientation of a line, the less effective it is in resisting horizontal loads.
For instance, a line orientated at a vertical angle of 45° is only 75% as effective in restraining the
ship as a line orientated at a 20° vertical angle. Similarly, the larger the horizontal angle between
the parallel side of the ship and the line, the less effective the line is in resisting a longitudinal
force.

Section 1

1.4 ELASTICITY OF LINES

The elasticity of a mooring line is a measure of its ability to stretch under load. Under a given
load, an elastic line will stretch more than a stiff line. Elasticity plays an important role in the
mooring system for several reasons:

• High elasticity can absorb higher dynamic loads. For this reason, high elasticity is

desirable for ship-to-ship transfer operations, or at terminals subject to waves or swell.

• High elasticity also means that the ship will move further in her berth and this could cause

problems with loading arms or hoses. Such movement also creates additional kinetic
energy in the mooring system.

• A third and most important aspect is the effect of elasticity on the distribution of forces

among several mooring lines. The simple four-line mooring pattern shown in the upper
portion of Fig. 1.5 is insensitive to the elasticity of the lines but is suitable only for boats or
very small ships. Larger ships require more lines resulting in load sharing and interaction
between lines. This becomes more complicated as the number of mooring lines
increases. Optimum restraint is generally accomplished if all lines, except spring lines,
are stressed to the same percentage of their breaking strength. Good load-sharing can
be accomplished if the following principles are understood:

The general principle is that if two lines of different elasticity are connected to a ship at the same
point, the stiffer one will always assume a greater portion of the load (assuming the winch brake
is set) even if the orientation is the same. The reason for this is that both lines must stretch an
equal amount, and in so doing, the stiffer line assumes a greater portion of the load. The relative
difference between the loads will depend upon the difference between the elasticities, and can
be very large.

The elasticity of a mooring line primarily depends upon the following factors:

• Material and Construction

• Length

• Diameter

Figure 1.6 demonstrates the significance of each of the above factors on load distribution. The
most important points to note are the appreciable difference in elasticity between wire lines and
fibre ropes and the effect of line length on elasticity. Case A) shows an acceptable mooring
where ropes of the same size and material are used. Case B) indicates the sharing of loads
between ropes of the same material but of different size and each rope is stressed to
approximately the same percentage of its breaking strength. However, Cases C) and D) are
examples of mooring arrangements that should be avoided.

Wire mooring lines are very stiff. The elongation for a 6 x 37 construction wire line at the loading
at which the material begins to be permanently deformed is about one percent of wire length.
Under an equivalent load a polypropylene rope may stretch ten times as much as a wire. Thus if
a wire is run out parallel to a conventional fibre line, the wire will carry almost the entire load,
while the fibre line carries practically none. Elasticity also varies between different types of fibre
lines and, although the difference is generally not as significant as that between fibre line and
wire, the difference will affect load distribution. High modulus polyethylene or aramid fibre lines,
for example, have much less elasticity than other synthetic fibre lines and would carry the
majority of the load if run out parallel to conventional synthetic lines.

The effect of material on load distribution is critical and the use of mixed moorings for similar
service, e.g. forward springs, is to be avoided. In some cases the fibre lines may carry almost no
load, while at the same time some of the wires are heavily loaded, possibly beyond their
breaking strength. The same could be true of mixed fibre lines of varying elasticity, although the
differences would generally not be as great unless the moorings also include high modulus
synthetic ropes.

Section 1

also be considered. Line elasticity varies directly with line length and has a significant effect on
line load. A wire line 60 m long will assume only about half the load of a 30 m parallel and
adjacent line of the same size, construction and material.

Elasticity of a given type of line also varies with its diameter, construction and age. Usually this
factor is not an important consideration since the load relative to a line's strength is the governing
factor rather than the absolute load. Conventional fibre ropes lose some elasticity with age.

1.5 GENERAL MOORING GUIDELINES

Consideration of the principles of load distribution in 1.4 lead to the following mooring guidelines.
These assume that the moored ship may be exposed to strong winds or current from any
direction.

• Mooring lines should be arranged as symmetrically as possible about the midship point of

the ship. (A symmetrical arrangement is more likely to ensure a good load distribution
than an asymmetrical arrangement.)

• Breast lines should be orientated as perpendicular as possible to the longitudinal centre

line of the ship and as far aft and forward as possible.

• Spring lines should be orientated as parallel as possible to the longitudinal centre line of

the ship.

Head and stern lines are normally not efficient in restraining a ship in its berth. Mooring facilities
with good breast and spring lines allow a ship to be moored most efficiently, virtually 'within its
own length'. The use of head and stern lines requires two additional mooring dolphins and
decreases the overall restraining efficiency of a mooring pattern when the number of available
lines is limited. This is due to their long length and consequently higher elasticity and poor
orientation. They should only be used where required for manoeuvring purposes or where
necessitated by local pier geometry, surge forces or weather conditions. Obviously, small ships
berthed in facilities designed properly for larger ships may have head and stern lines because of
the berth geometry.

• The vertical angle of the mooring lines should be kept to a minimum.

The 'flatter' the mooring angle, the more efficient the line will be in resisting horizontally-applied
loads on the ship.

A comparison of Cases 1 and 3 in Fig. 1.4 demonstrates that a ship can usually be moored
more efficiently within its own length. Although the same number of lines is used in each
situation, Case 1 results in a better load distribution, minimising the load in any single line.

• Generally, mooring lines of the same size and type (material) should be used for all

leads. If this is not possible, all lines in the same service, i.e. breast lines, spring lines,
head lines, etc. should be the same size and type. For example, all spring lines could be
wire and all breast lines synthetic.

'First lines ashore' are sometimes provided on very large ships to assist in the initial approach
and positioning of the ship alongside. These lines often have high elasticity and are unlikely to
add to the final restraining capacity of the system unless all lines in that group are of the same
material.

Synthetic tails are often used on the ends of wire lines to permit easier handling and to increase
line elasticity. Tails may also be used to increase the elasticity of low stretch ropes made from
high modulus polyetheylene or Aramid fibres (see Section 6.5).

• If tails are used, the same size and type of tail should be used on all lines run out in the

same service.

The effect of attaching 11 metre long tails, made from both polyester and polyamide, to steel wire
and HMPE mooring lines is shown in the following graph. It should be noted that longer tails will

Section 1

have a significant impact on the assemblies' elasticity.

FIGURE 1.7: COMPARISON OF STEEL WIRE VERSUS HMPE MOORING LINES WITH AND

WITHOUT 11 metre TAILS

(References 10 and 11)

•

Mooring lines should be arranged so that all lines in the same service are about the same
length between the ship's winch and the shore bollard. Line elasticity varies directly with
line length and shorter lines will assume more load.

1.6 OPERATIONAL CONSIDERATIONS

The above mooring guidelines were developed to optimise load distribution to the moorings. In
practice, final selection of the mooring pattern for a given berth must also take into account local
operational and weather conditions, pier geometry and ship design. Some pilots, for example,
desire head and stern lines to assist ships moving into, along, or out of a berth, while others may
use spring lines for this purpose. Head and stern lines would be advantageous at berths where
the mooring points are too close to the ship and good breast lines cannot be provided, or where
the bollards are located so that the lines will have an excessive vertical angle in the light
condition. These excessive angles would result in considerably reduced restraint capability.

High winds and currents from certain directions might make it desirable to have an asymmetrical
mooring arrangement. This could mean placing more mooring lines or breast lines at one end of
the ship.

The other factor to consider is the optimum length of mooring lines. It would be desirable to keep
all lines at a vertical angle of less than 25°. For example, if the ship's chock location is 25m above
the shore mooring point, the mooring point should be at least 50m horizontally from the chock.

Long lines are advantageous both from a standpoint of load efficiency and line-tending. However,
where conventional fibre ropes are used, the increased elasticity can be a disadvantage by
permitting the ship to move excessively, thereby endangering loading arms. Figure 1.8 illustrates
the effects of line lengths on line-tending requirements.

Section 1

mixed moorings (synthetic ropes and wire lines), all wire moorings (with and without synthetic
tails) to systems using high modulus synthetic fibre ropes. Rated brake capacities, winch and
fairlead locations can vary significantly from ship to ship. Ship crews will have varying degrees of
expertise in mooring matters and varying philosophies concerning maintenance and/or
replacement of critical items of mooring equipment.

The terminal can utilise a number of concepts in modern mooring management to reduce the
possibility of ship break-out. These are:

• To develop guidelines for the safe mooring of ships for the operating environment

existing at the terminal, together with recommended mooring plans.

• To ensure that terminal mooring equipment is positioned and sized for the range of ships

being handled, is properly maintained and clearly marked with its SWL.

• To obtain information from the ship prior to arrival concerning the ship's mooring

equipment.

• To examine the ship's mooring equipment after berthing to determine what modification,

if any, must be made to standard guidelines in view of the state of maintenance, training
of crew, etc.

• To check on the effectiveness of line tending periodically, either visually or by the

instrumentation of mooring hooks.

• To take whatever action is deemed appropriate to ensure stoppage of cargo transfer,

disconnection of loading arms and removal of the ship from the berth should the ship fail
to take appropriate measures to ensure safety of mooring or should environmental
conditions reach or exceed the operating limits as agreed and documented in the
Ship/Shore Safety Check-List.

1.7.1 Operating Limits

Another important aspect in restraining the ship at its berth is the movement of the ship. No
simple formula can be offered for the ship movement, although this is generally included in the
output of computer calculations. Movement of the ship due to environmental loads can exceed
loading arm operating limits before the strength limits in the mooring lines are reached. Similarly,
limits and requirements may apply to gangways, particularly shore-based equipment
incorporating a tower or a long span from the jetty to the ship. This is especially true for synthetic
line systems. Under worsening environmental conditions, the loading arms and gangways may
therefore have to be disconnected at lesser wind and current conditions than those used as a
design basis for the mooring system.

Environmental operating limits should be established for each berth and should be detailed on
the Ship/Shore Safety Check-List. In addition, ship's staff should be advised of any limitations on
ship movement due to the operating envelopes of shore equipment such as hard arms, fenders
(compression limits) and gangways and the actions to be taken should these be reached.

The concept of 'manageable escalating events' is applied when establishing environmental limits
and the following illustrates this principle:

• the loading arms may typically be purged and disconnected when the wind reaches 30

knots (15 metres/second) and preparations made to leave the berth.

• tugs may be requested to hold the ship alongside up to wind speeds of 35 knots (18

metres/second).

• the gangway will be stowed and the ship will be ready to leave the berth at the Master's

judgement when the wind reaches 35 knots (18 metres/second).

• the ship's mooring lines should be able to hold the ship in position with wind speeds of

60 knots (31 metres/second) and the maximum tension in any one line should not
exceed 55% of the MBL.

Section 1

• at wind speeds above 60 knots (31 metres/second), line tensions will exceed 60-65%

MBL and winch brakes will start to render. The ship will be in a potentially dangerous
situation.

For ships moored at a Single Point Mooring, the practical safety limitation may well be related to
physical ability of the crew to handle hoses and work safely rather than either ship movement or
mooring loadings.

1.7.2 Operating Guidelines/Mooring Limits

In the past, operating guidelines and mooring limits have generally been developed empirically.
With the advent of computers and the ready availability of specialised programs, allied with the
development of more accurate wind and current drag coefficients, guidelines can be developed
systematically which can provide the limits for various classes of ships with varying mooring
capabilities. It is recommended that mooring analysis are undertaken for facilities to validate
recommended mooring arrangements and plans.

The following tables depict how data from a mooring analysis may be presented in order to assist
ship and terminal staff understand and implement operating guidelines. In the examples shown in
Tables 1.2 and 1.3, the maximum line and fender load, and ship surge and sway at the manifold,
is given for an oil tanker and a very large LNG carrier. Where mooring loads exceed the 50% of
MBL (synthetic) and 55% of MBL (steel wire) limitations, additional shore lines or very small
reductions in weather criteria may bring the mooring under the tension limit. Conditions shown as
'not safe' would require a very large reduction in weather criteria and would probably result in
unacceptable increases in downtime.

The information generated can be used for a number of purposes:

• To decide whether a given ship can be moored at a given berth under the expected

weather conditions.

• To determine when to discontinue cargo transfer and to disconnect loading arms.

• To advise the ship when it would be desirable to take on ballast to reduce its freeboard.

• To advise the ship when it would be desirable to have tugs available to assist in

maintaining the ship's position at the jetty while preparations are made to vacate the
berth.

Three significant wave heights are considered in the examples shown in the tables to establish
the sensitivity to line tension and ship excursion over the range 1.0 m, 1.5 m and 2.0 m. These
wave heights cover the typical range that would be experienced up to the practical limit of 2.0 m.
It can be seen that at the higher wave heights the 11 m tails are inadequate and that longer 22 m
tails are required. Conversely, at lower wave heights the 11 m tails are adequate. Another very
important factor is the elasticity of the tail where the high stretch polyamide provides lower
tensions than the lower stretch polpropylene/polyester and 100% polyester tails.

Section 1

Ship Excursion at

manifold (metres)

(1)

Mooring line on

winch and tail

description

Wind

direction

Highest line

tension %

(1)

Fwd

Aft

Out

Fender

load

(tonnes)

(1)

Steel wire with 11m

polyamide tail

41
56

(2)

0.2
0.2

0.1
0.2

0.3
0.5

283
315

Steel wire with 22m

polyamide tail

30
38
47

0.2
0.2
0.2

0.2
0.3

0.4
0.5
0.6

284
314
323

HMPE with 11m

polyamide tail

37
51
60

0.2
0.2
0.2

0.1
0.2
0.3

0.3
0.5
0.6

283
315
323

HMPE with 22m

polyamide tail

29
36
45

0.2
0.2
0.2

0.2
0.3

0.4
0.5
0.6

283
314
323

pp/polyester or 100%

polyester

Offshore

25
28
33

0.2
0.2
0.2

0.2
0.3

0.4
0.5
0.6

282
315
323

Steel wire with 11m

polyamide tail

37
52
60

0.1
0.2
0.2

0.1
0.2
0.3

0.2
0.4
0.5

302
320
321

Steel wire with 22m

polyamide tail

25
34
44

0.1
0.1
0.2

0.1
0.2
0.3

0.2
0.4
0.5

302
320
322

HMPE with 11m

polyamide tail

34
47
62

0.1
0.2
0.2

0.1
0.2
0.3

0.2
0.4
0.5

302
320
322

HMPE with 22m

polyamide tail

25
33
42

0.1
0.1
0.2

0.1
0.2
0.3

0.2
0.4
0.5

302
320
322

pp/polyester or 100%

polyester

Onshore

20
26
32

0.1
0.1
0.2

0.1
0.2
0.3

0.2
0.4
0.5

302
320
322

NOTES FOR TABLE

(1)

Ref Highest Line Tension:
top row 1.0 m, middle row 1.5
m, lower row 2.0 m significant
wave heights

(2) NS= not a safe condition due to

many lines overloading

TABLE 1.2 TANKER 107,000 DWT, 35 KNOT WIND 315º (offshore) and 045º (onshore); 5 KNOT

CURRENT 350º; and 2 METRE, 10 SECOND 45º SWELL

(Reference 12)

Section 1

Ship Excursion at

manifold (metres)

(1)

Mooring line on

winch and tail

description

Wind

direction

Highest line

tension %

(1)

Fwd

Aft

Out

Fender

load

(tonnes)

(1)

Steel wire with 11m

polyamide tail

38
49
60

0
0
0

0.4
0.5
0.6

0.2
0.2
0.3

292
318
322

Steel wire with 22m

polyamide tail

30
36
43

0
0
0

0.6
0.7
0.9

0.2
0.2
0.3

289
317
322

HMPE with 11m

polyamide tail

36
45
56

0
0
0

0.4
0.5
0.6

0.2
0.2
0.3

291
318
322

HMPE with 22m

polyamide tail

29
35
41

0
0
0

0.6
0.7
0.9

0.2
0.2
0.3

289
317
322

HMPE with 11m

pp/polyester or 100%

polyester tail

41
62

(2)

0
0

0.3
0.4

0.1

309
324

HMPE with 22m

pp/polyester or 100%

polyester tail

Offshore

37
48
60

0
0
0

0.4
0.5
0.6

0.2
0.2
0.3

283
316
322

Steel wire with 11m

polyamide tail

34
45
60

0
0
0

0.5
0.6
0.7

0.1
0.2

309
324
324

Steel wire with 22m

polyamide tail

26
32
39

0
0
0

0.7
0.8
0.9

0.1
0.2

309
324
324

HMPE with 11m

polyamide tail

31
42
56

0
0
0

0.5
0.6
0.7

0.1
0.2

309
324
325

HMPE with 22m

polyamide tail

25
31
51

0
0
0

0.7
0.7
0.8

0.1
0.2

310
324
324

HMPE with 11m

pp/polyester or 100%

polyester tail

34
47
60

0
0
0

0.5
0.5
0.7

0.1
0.2
0.2

291
318
322

HMPE with 22m

pp/polyester or 100%

polyester tail

Onshore

35
47
60

0
0
0

0.4
0.5
0.6

0.1
0.1
0.2

308
324
324

NOTES FOR TABLE

(1) Ref Highest Line Tension:

top row 1.0 m, middle row 1.5
m, lower row 2.0 m significant
wave heights

(2) NS= not a safe condition due to

many lines overloading

TABLE 1.3: LNG CARRIER 267,000m

, 35 KNOT WIND 315º (offshore) and 045º (onshore); 5

KNOT CURRENT 350º; and 2 METRE, 10 SECOND 45º SWELL

(Reference 12)

Section 1

1.7.3 Joint Terminal/Ship Meeting and Inspection

As soon as practicable after berthing, it is recommended that terminals have their representative
board the ship to establish contact with the Master or his designated representative. At this
meeting the Terminal Representative should provide information relating to shore facilities and
procedures. In addition he should, in concert with the Ship Representative:

• Complete the Ship/Shore Safety Check-List in line with guidance given in ISGOTT

(Reference 4) and, where appropriate, physically check items before ticking off.

• Obtain details of moorings and winches, including state of maintenance.

• Review forecasted weather and arrange for the Master to be advised of any expected

changes.

• Assess freeboard limitations.

• Determine the conditions at which cargo transfer will be discontinued and loading arms,

hoses and gangway will be disconnected and agree the precautions to be taken under
high mooring load situations. Document operating limits on the Ship/Shore Safety Check-
List.

1.7.4 Instrumented Mooring Hooks or Visual Inspection of Mooring Lines

The terminal should monitor the ship's line tending activity by visual inspection of the mooring
lines, particularly during cargo transfer and periods of changing environmental conditions.

In addition to the above, where an appropriate need has been identified, and dependent on the
physical environment at the berth, it may be desirable to install mooring line load measurement
apparatus. This equipment has been installed at a number of large tanker berths and at many
LNG berths. It measures the line loads and has a central read-out in the terminal operation's
control room. Should the line loads become high or the lines become slack, the terminal operator
can advise the ship accordingly.

In some terminals mooring tension information is transmitted to a shipboard fixed or portable
display for direct access by ship’s staff. In any case, the terminal should inspect lines
periodically. If poor line tending by ship’s staff is observed, the terminal should notify the ship.

1.8 SHIP MOORING MANAGEMENT

Good ship mooring management requires a knowledge of good mooring principles, information
about the mooring equipment installed on the ship, proper maintenance of this equipment, and
good, seamanlike line tending.

Officers in charge of line tending and personnel assigned to tend lines should be aware of the
capabilities of the equipment installed on their ship. Winches should be marked to show the
design holding capacity. The torque required on the hand wheel or lever to achieve the required
brake rendering should be documented. Specifications of the mooring lines should also be
available.

Recommendations concerning the proper direction of reeling or pay-out of the wire on the drum
should be followed and the drum should be marked accordingly to prevent any possibility of error
(see Section 7.4.2.6).

1.8.1 Line Tending

The objective of good line tending is to ensure that all lines share the load to the maximum
extent possible and to limit the ship's movement off the berth or alongside the berth. Pre-
tensioning of lines (that is loading a line with a winch prior to the application of environmental
forces) reduces ship movement and improves the load distribution when lines of different lengths
and elasticities are being used.

Section 1

To prevent excessive movement of the ship along the pier face, it is very important to tend spring
lines differently from breast lines. Tending head or stern lines presents a special problem (which
is one more reason why they are not recommended). They must be tended like either spring or
breast lines depending on whether longitudinal or transverse restraint is more critical. For
example, if a high longitudinal current on the bow is expected, the bow line should be pre-
tensioned while the stern line is tensioned only to take up any slack. The following general rules
apply to line-tending.

• Generally, slack lines should be hauled in first. Slack lines may permit excessive

movement of the ship when there is a sudden change in the environment.

• Only one line should be tended at a time. Any time a line is tended, it temporarily

changes the load in other lines and may increase it. The simultaneous tending of two
lines may therefore give erratic results or even an overload.

• Whenever a spring line is tended, the opposite spring must also be tended, but not

simultaneously. Rendering or heaving-in on only one spring line may cause excessive
movement of the moored ship along the pier face.

• Fender compression should be observed during discharge or during a rising tide. Fender

compression may be caused by over-tight breast lines. If there is high fender
compression which is not caused by on-shore winds or currents, the breast lines must be
slackened.

1.9 EMERGENCY AND EXCESSIVELY HIGH MOORING LOAD

CONDITIONS

Overloading of mooring lines is evidenced in a number of ways; for example, by direct measure-
ments of mooring line loads, by direct observation of the moorings by experienced personnel, or
by predictions made by those having a knowledge of the effects of wind and current on the ship
mooring system or by winch slippage.

In general, ship's moorings should not be subjected to environmental forces in excess of the
designed environmental limits. In the event of mooring lines being, or likely to be, subjected to
excessive loads, consideration should be given to immediately departing the berth. Should this
not be practicable, the following precautions should be considered:

• Call out crew, linemen, mooring boats, tugs and put the ship's engines on readiness.

• Confirm that winch brakes are correctly applied.

Do not release brakes and attempt to heave in.

• Discontinue cargo operations.

• Disconnect loading arms and gangways.

• Should time and ship condition permit, consider taking-on ballast to reduce freeboard if

loads are due to high wind conditions.

•

• Run extra moorings as available together with any shore mooring available to augment

ship's equipment.

In a developing potential emergency situation, the point at which the ship leaves the berth may be
dictated by limits, such as hose handling capability, the use of tugs and work boats and not solely
mooring line loads or ship movement. It must be emphasised that it is the ship’s Master who is
responsible for the safety of the ship and he must decide whether it is safe to vacate the berth or
whether, by making a hurried unberthing manoeuvre, he will in fact place his ship or personnel in
greater danger. There are also certain berths where tidal conditions or manoeuvring areas may

Section 1

be such as to prevent the unberthing of the ship at certain times.

1.10 LIMITATIONS ON USE OF TUGS AND BOATS

Tugs can perform a very useful function in holding the ship against the berth in order to reduce
the strain on moorings while preparations are made to vacate the berth. However, in deteriorating
weather conditions, the ready availability of tugs may be compromised.

Care should be exercised when high horsepower tugs are engaged to keep the tanker alongside
a jetty while hoses or cargo arms are disconnected. The application of excessive power could
result in over-compression of the fenders and damage to the ship's side. To minimise the
possibility of damage, tug push points should be clearly marked on the ship’s hull. It must also be
recognised that tugs have certain operating limits and that, particularly in berths subject to waves,
these limits are likely to be exceeded.

In the case of Multi-Buoy Moorings, boats may be required to release mooring lines from buoys.
At jetties, boats may be required to put line handlers on detached mooring dolphins. As with tugs,
the boats may have operating limits which will be exceeded under extreme conditions.

1.11 GENERAL RECOMMENDATIONS.

1.11.1 Recommendations for Berth Designers

• The mooring facilities provided at the berth should be such as to permit the largest ship

which is to be accommodated to remain safely moored alongside in the maximum
environmental limits established for the specific site.

• The wind and current forces on the ship should be calculated for the wind and current

conditions under which the ship may remain moored at the berth, using the procedures
covered in Section 2 of these guidelines. At exposed locations, the impact of dynamic
loads will need to be considered in addition to the calculation of static loads. Most
probable maximum (MPM) loads will need to be assessed when establishing allowable
load criteria for moorings (see Section 2.5).

• Allowable loads in any wire mooring line should not exceed 55% of its Minimum

Breaking Load (MBL). For synthetic lines, including wet polyamide, loads should not
exceed 50% of the line's MBL, see Section 1.7.1.

• The following principles should be applied when designing the layout of mooring

facilities on the berth:

Mooring points should be disposed as nearly as possible symmetrically about the centre
point. Breast moorings should be provided such that they will emanate from points near
the fore and aft ends of the ship and as nearly as possible perpendicular to the fore and
aft line of the ship.

The length of mooring lines at conventional berths should be within the range 35 to 50 m
and, where intended for the same service and practicable, be equal.

Sufficient mooring points should be installed to provide a satisfactory spread of moorings
for the range of ship sizes which the berth is to accept. VLCCs are preferably moored by
breast lines and spring lines only, although on berths designed to accept a range of ship
sizes, the mooring points will inevitably be such that smaller ships may need to use head
lines and stern lines in addition to breast lines.

The heights of mooring points should be such that vertical angles will be as small as
practical and, if possible, should not exceed 25º from the horizontal.

• Breasting dolphins should preferably be positioned at a distance apart of one third of the

overall length of the ship. At berths accommodating a range of ship sizes the spacing of

Section 1

breasting dolphins should preferably be located so that they provide a breasting face
between 25% and 40% of the ship’s overall length about the ship's midship point to
ensure compatibility with the ship's parallel mid-body and balanced mooring forces. For
fine-lined ships, lesser distances may be required to ensure that dolphins are within the
parallel body.

• Quick release hooks should be provided with a SWL not less than the MBL of the largest

rope anticipated and be supplemented by capstans or winches and fairleads to enable
the handling of large ship's moorings.

• Shore based mooring equipment should be provided to augment shipboard equipment

when the operating conditions at the berth exceed the Design Environmental Conditions.

1.11.2 Recommendations for Terminal Operators

• Terminal Operators should have a good understanding of mooring principles, of the

design of the mooring system for the berth, of the loads likely to be experienced in the
mooring system under varying conditions of wind and current and to have a clear
appreciation of the operating limits applying to the various types of ships and mooring
systems which may be used in the berth.

• Terminal mooring equipment, including bollards, mooring hooks and/or rollers and

pulleys should be clearly marked with their SWL.

• Terminal Operators should recognise the problems likely to arise from the use of mixed

moorings and be aware of the need for effective application of winch brakes and good
mooring management while the ship is in the berth.

• Ship-to-shore liaison should be established by the Terminal Operator prior to arrival. A

joint agreement is required with the ship on the way in which the ship will actually be
moored, and on continuing liaison on mooring matters during the time the ship is in the
berth; particular attention being paid to the procedures to be followed in managing
escalating events and emergencies.

1.11.3 Recommendations for Ship Designers

• The mooring facilities provided on the ship should be such as to permit the ship to

remain safely moored under the Standard Environmental Criteria alongside a berth
which is provided with a standard arrangement of mooring points.

• Wind and current forces on the ship should be calculated applying the Standard

Environmental Criteria and the coefficients contained in Appendix A and by using the
methods described in this Guideline. This calculation will determine the number, size and
disposition of moorings required on board.

• Loads in any wire mooring line should not exceed 55% of the line's MBL. For synthetic

lines, including wet polyamide, loads should not exceed 50% of the line's MBL.

• Mixed moorings, comprising full length synthetic ropes used in conjunction with wires,

are not recommended.

• Wire or HMPE ropes should be the standard mooring equipment for all large tankers and

it is recognised that ropes greater than 44 mm diameter may require special handling
arrangements in terminals.

• Synthetic ropes may be used as the first line ashore for positioning the ship at either

end, preferably by means of handling and storage winches. These ropes should not be
considered as contributing to the restraint of a ship moored principally with wires.

• When tails are fitted to mooring ropes they should have an MBL at least 25% higher than

that of the mooring lines to which they are attached. Polyamide tails should have a 37%
higher MBL than the mooring line to take account of loss of strength when wet. In
general, tails should have a length of not less than 11 m, and be subject to rigorous
examination and renewal procedures, as recommended in Section 6.

Section 1

• Winches for handling mooring ropes may be either of the split drum or undivided drum

type; the relative merits of the two types are described in Section 7.3.

• Automatic winches are not recommended, but if fitted must have a capability to

disengage the automatic operational features.

• Winch brakes should be designed to hold 80% of the line's MBL and have the capability

to be adjusted down to 60% of the line's MBL, at which level they should be set in-
service, see Section 7.4.6. They should be properly maintained and routinely tested.

•

The layout of moorings should be such as to provide:

symmetry about the mid length and to provide the design numbers of moorings on
each side of the ship,

breast lines sited as near as possible to the end of the ship,

moorings used in the same service to be as nearly as possible of the same length
inboard of the ship,

suitable chocks and fairleads to be provided in order to ensure correct alignment of
moorings,

bitts to be positioned for supplementary moorings.

• Minimum safety factors listed in Table 4.1 are based upon the appropriate design criteria

and loading assumptions, and should be incorporated in all new equipment and mooring
fittings.

• All equipment and fittings should be clearly marked with their SWL.

1.11.4 Recommendations for Ship Operators

• The principles of good mooring, including the dangers associated with mixed moorings,

should be understood by ship operators. Particular attention should be given in ship's
instructions to the proper application of winch brakes, the maintenance of moorings and
winch brakes, good line tending procedures and the practices to be observed in the case
of mooring emergencies.

•

Each ship should be provided with information on the design of the mooring system, with
examples to show the loads likely to be experienced under particular conditions and to
illustrate those situations under which the limit of the system is likely to be reached.

Section 2

Mooring Restraint and

Environmental Criteria

2.1 GENERAL CONSIDERATIONS

This Section provides guidance to assist in the determination of the strength and number of
mooring lines for new ships to facilitate the design of ship's mooring equipment.

Section 2.2 details the environmental criteria used to calculate the forces on the ship at the
design stage. Section 2.4 then details the calculations required to determine the numbers of
mooring lines and capacity requirements for deck equipment for a new ship. Finally, section 2.5
details the site-specific environmental criteria used to determine the fitness for purpose and
safety for a given ship and terminal.

In order to design a ship's mooring system, the environmental loads likely to act upon the ship
must be determined.

These environmental loads can be highly variable from terminal to terminal. To ensure a
minimum standard is met for mooring equipment on ships engaged in worldwide trades, the
Standard Environmental Criteria should be used, as detailed in section 2.2. The Standard
Environmental Criteria apply to the design of the ship mooring system and are not criteria for
pier design nor a required operating capacity for a pier/ship mooring plan. These are further
considered in section 2.5. These parameters are not intended to cover the worst possible
conditions, since this would be neither practical nor reasonable.

In situations where the Standard Environmental Criteria are likely to be exceeded, such as bank
effect at a river berth with extremely strong currents, additional measures must be taken such as
doubling mooring lines, requesting tug assistance or leaving the berth.

The wind and current drag coefficient data are detailed in Appendix A.

2.2 STANDARD ENVIRONMENTAL CRITERIA

The aim of this section is to provide environmental criteria to calculate forces on the ship that are
used to determine the number and strength of mooring lines, and the requirements for deck
equipment for new build ships.

For all ships above 16,000 tonnes deadweight intended for general worldwide trading, the
mooring restraint available onboard the ship as permanent equipment should be sufficient to
satisfy the following conditions:

60 knots wind (defined below) from any direction simultaneously with :

3 knots current at 0º or 180º;

2 knots current at 10º or 170º;

0.75 knots current from the direction of maximum beam current loading.

Section 2

For tankers, water depth to draft ratios for these conditions are to be taken as 1.1 when loaded
and 3.0 when in ballast.

For gas carriers above 150 metres in length the same standard environmental criteria should be
applied. However, the water depth to draft ratio may be taken as 1.1 for all conditions, since the
draft of a gas carrier changes little during normal cargo transfer operations.

While a number of terminals have a minimum depth to draught ratio alongside the berth of 1.05
this ratio will inevitably prevail around low slack water when average current velocities would be
less than when the water level is at a depth to draught ratio of 1.1. It is therefore suggested that
the average velocities previously recommended be used with the 1.1 ratio.

When a terminal designer is reviewing the need for shore augmentation, it will be necessary to
be more precise and actual site data should be used for calculations.

Wind velocity is the velocity measured at the standard datum height of 10 m above ground or
water surface and is representative of a 30 second average mean velocity. The selection of the
30 second wind is based on the time it takes the forces in a mooring system to respond to wind
velocity changes. Thirty seconds is a typical value for a ballasted VLCC. Smaller ships will
respond more quickly and a fully laden VLCC may require 60 seconds to respond. However, for
consistency, a 30 second average period is suggested for all ship sizes and loading conditions.

The current velocity is to be taken as the average velocity over the draft of the ship.

The above criteria are intended to cover conditions that could readily be encountered on
worldwide trade, but they cannot possibly cater for the most extreme combination of
environmental conditions at every terminal worldwide. Particularly exposed terminals, or those
where for some reason the criteria are likely to be exceeded, are expected to supplement ships'
mooring restraint with appropriate shore-based equipment. For example, this may include shore
lines on winches run to the ship and fastened on bitts.

Where a ship is operating exclusively on a dedicated route using terminals whose specific
environmental data is available, the recommended criteria may be revised to suit the local
conditions.

Dynamic effects are not included in the above criteria and are addressed in Section 2.5.

2.3 CALCULATION OF FORCES

Computer programs are widely available to carry calculate mooring forces for any combination of
wind and current speeds and angles. Example wind forces using first principle formulae are
detailed in Appendix A.

Any program should use the appropriate wind and current drag coefficients for the ship. In cases
where specific data is not available, the wind and current drag coefficient data in Appendix A
should be referenced.

2.4 MOORING RESTRAINT REQUIREMENTS

Having determined the environmental forces acting on the ship, it is necessary to calculate the
strength and number of mooring lines required to balance these forces.

In calculating mooring restraint, the three-dimensional coordinates of all ship and terminal
mooring points must be known or assumed, together with the elastic characteristics of the
mooring lines and fenders. When assessing mooring line elasticity, it should be based on the full
length of line from winch to shore bollard.

The structural characteristics of mooring and breasting dolphins, may need to be accounted for
if these structures are compliant.

Section 2

Computer calculations are especially suitable to explore the adequacy of the mooring system of
an existing or planned ship at a terminal known to have unusual environmental conditions or
mooring geometry.

2.4.1 Basic Principles of Mooring Calculations

A ship at a jetty or sea island is held in the berth by a combination of mooring lines and breasting
dolphins which resist the forces applied to the ship by wind, current, waves and other
environmental factors. There are multiple mooring lines which connect from several locations on
the ship to several mooring points on the jetty or sea island. It is a system in which the forces in
the lines cannot be calculated solely by the principle of static equilibrium, so the solution must
consider the elasticity of the components. Basically, the ship and mooring system together may
be considered as a two-dimensional elastic system such that when a load is applied to the ship,
the ship will move a small but determinable amount. By determining the amount of movement of
the ship, the forces in the mooring lines and breasting dolphins can be determined.

For steady-state forces on the ship (current and wind forces are considered steady-state forces
for the purposes of the analysis), the forces in the mooring lines are determined using the
following basic principles or characteristics:

2.4.1.1 The Principle of Static Equilibrium

The sums of the components of the forces in the mooring lines and breasting dolphins in each
principal direction and the moment of forces about the centre of the ship are equal and opposite
to the sums of the components of the applied forces (current and wind) and the moment of these
forces. The principal directions are ahead (or astern) and abeam, and the moment is a yawing
moment.

2.4.1.2 The Load/Deflection Characteristics of each Mooring Line and Breasting Dolphin

For each there is a relationship between its elongation (for mooring lines in tension) or inward
deflection (for breasting dolphins in compression) and the force in the member.

For mooring lines, the load/deflection characteristic is dependent on the material and
construction of the line, its diameter and the loaded length (i.e. from the ship's winch to the
mooring point on the jetty or sea island). Mooring lines become stiffer (less stretch for a given
load) with use, and the characteristic for used line is normally employed for calculating loads
rather than the characteristic for new line. The characteristics can be obtained from line
manufacturers or suppliers.

For breasting dolphins, the characteristics for manufactured fender units are available from the
manufacturer. Deflection of the dolphin structure, if significant, can be calculated from the
properties of the structure.

2.4.1.3 The Geometrical Relationship Between the Parts of the System

The elongation of each mooring line and deflection of each breasting dolphin can be calculated
from the amount of surge, sway and yaw at the centre of the ship. Since the ship is essentially a
rigid element, each chock through which a line passes effectively moves in relation to the
mooring point, thus changing the distance between the chock and the mooring point on the jetty
or sea island.

Using the above principles or system characteristics, the forces in the mooring lines for wind and
current forces should be calculated within the software using the following general procedure:

1. Calculate the applied forces in the fore/aft direction and the beam direction and the yaw

moment for wind and current.

2. Determine the elasticity of the entire mooring system from the load/deflection

characteristics of each component and the geometry of the system. The elasticity of the
system is expressed in terms of amount of surge, sway and yaw per unit force in each
principal direction and per unit yaw moment.

3. Calculate the total amount of surge, sway and yaw at the centre of the ship by

Section 2

multiplying the amount per unit force and moment determined in step 2 by the applied
forces and moment calculated in step 1. Then calculate the new location of each chock
point.

4. Determine the force in each mooring line and breasting dolphin by calculating the stretch

in the line (or compression of the dolphin), allowing for any line pre-tensions, based on
the movement of the tanker and the load/deflection characteristic.

5. Several iterations of this procedure may be necessary before converging on to the

equilibrium position of the ship.

FIGURE 2.1: GENERIC MOORING LAYOUT USED FOR COMPUTATIONAL PURPOSES

2.4.2 Standard Restraint Requirements

To obtain a uniform standard of mooring equipment for ships not designed for a specific trade or
terminal, it is recommended that the ship designer:

1. Follows the principles provided in Section 3 regarding the placement of winches, chocks,

and fairleads.

2. Assumes breast lines to be at an angle of 75° to the longitudinal axis of the ship. A

horizontal angle of 10° to the side of the ship should be assumed for spring lines.
Maximum vertical angles of 25° should be assumed for the lightest ballasted condition.
These criteria therefore determine the position of mooring points for a generic mooring
line layout, as illustrated in Figure 2.1.

3. Calculates the number of breast lines and spring lines that would be required for the

'Standard Environmental Criteria' and for the generic mooring layout in Figure 2.1.

Section 2

2.5 SITE-SPECIFIC ENVIRONMENTAL DATA AND MOORING

LINE LOADS

This Section is to help ship owners and terminal operators ensure that the mooring lines, deck
and shore structures and equipment are suitable at a specific terminal. Further details for
terminals are outlined in Section 1.11.

Unlike offshore moorings, there are no standards, codes or recommended practices for pierside
moorings that define the return periods for wind, wave and current. Determination of appropriate
values should take into account operational constraints and the reliability of the environmental
data.

Two categories of environmental effects should be considered, namely, a) steady state forces
(mean wind, mean wave drift force, current) and b) wave frequency vessel motions.

The response to waves can be separated into two quite different components, first order where
the ship moves directly and immediately with each wave encountered, and second order where
the waves deflect off the hull and generate steady or slowly changing drift forces. Although low
frequency vessel motions due to varying wave drift forces can be important in deepwater
moorings, they are not usually significant for pierside moorings and can be treated as a steady
force, like wind and current. Drift forces are proportional to the wave height squared and are
greatest in short period waves.

On the other hand, first order wave motions are directly proportional to wave heights, and are
greatest in long period waves. Such motions can be treated as independent of the mooring
properties. Their greatest magnitude should be estimated from model tests or calculated using
suitable software, or measured from observation of the actual motions of ships in the worst local
wave conditions at a particular mooring berth. Piers constructed on piles are effectively
transparent to waves, but solid piers can have a significant influence by reflecting the waves and
interacting with the waves generated by the ship motions. Other factors affecting wave motions
for a given ship include water depth, wave height, wave period, and wave direction.

The properties of local wind blown waves, as opposed to swell emanating from a distant source
(typically a storm many hundreds of miles away), are generally different and independent. Their
effect on ship motions should be estimated separately and then combined by taking the root of
the sum of the squares of the two motions induced by waves and swell (RMS value).

Wave motions should be allowed for in calculating the mooring line forces by first analysing the
mooring response without any wave motion, and then adding the ship motion amplitude on each
fender and mooring line, taking into account its position and orientation. The resulting additional
line tensions and fender reactions should be calculated from their stiffness properties.

Static and dynamic computer programs are available, but static analysis is suitable in cases
where the timescale of variations in the mean forces due to wind and current is slow enough for
the mooring system to respond in a quasi-static manner, for example, slowly changing tidal
conditions. Wind gusts shorter than 30 seconds can normally be assumed to have no significant
effect on the mooring response, and the 30 second mean wind speed should be used in a static
analysis. Dynamic simulation may be necessary in situations where forces change rapidly and
last longer than the time it takes for the mooring system to respond. Typical situations involving
rapid changes calling for a dynamic analysis are:

•  Movement after a sudden line failure.
•  Sudden gust of wind or meteorological squall.
•  Rapid change of current at turn of tide, or local current eddies.
•  Effect of a passing ship.

Section 2

If the mooring is exposed to waves it may also be necessary to carry out an analysis to estimate
the ship motion response. It may be assumed that the stiffness of the mooring system is too low
to appreciably affect the first order wave motions, which can therefore be decoupled from the
relatively slow excursions of the mooring system due to wind or current. The additional line
tensions due to wave motions are calculated by superposing these motions on to the position
calculated without wave motion. The most probable greatest motion in any given sea-state can be
combined with any other environmental forces. Such a frequency domain approach can be
adopted when using either a static or dynamic method of analysis. Alternatively, with a dynamic
analysis it is also possible to simulate the individual wave motions in the time domain, although
this generally requires longer simulations to obtain reasonable probabilities for the greatest
mooring forces.

In some locations, very high current, large or long period swell or strong winds (or any other
force) may require the operational limits to be reduced and/or supplementary shore lines to be
used.

2.5.1 Most Probable Maximum (MPM) Loads

When a ship motion analysis is made in the frequency domain, the wave induced movement in
the direction of each line at its fairlead is calculated using the appropriate linear response
amplitude operators (RAO’s) for the ship in conjunction with a suitable wave spectrum for the
mooring berth exposed to waves and/or swell. The significant amplitude of in-line wave induced
movement A

sig

(which is twice the RMS amplitude) can then be calculated for any given sea-state

defined by a significant wave height and a mean or peak energy wave period.

In a constant sea-state over a period of N waves, standard Rayleigh probability theory for waves
and wave responses indicates that the most likely maximum amplitude of wave motion A

max

given by:

)

log

(

max

sig

It is normal to specify sea-states for typical durations of 3 hours. As an example, if the mean
period of a 3 hour sea-state were 9 seconds, the most likely maximum wave induced motion
would be 1.88 times the significant amplitude. This motion can be superposed on the movement
attributable to the steady or slowly varying environmental forces acting, and the peak line
tensions calculated from the line stiffness properties.

This approach uses the short-term wave statistics for a given sea-state. Other methods have to
be used to obtain the worst sea-state likely to be encountered in the long-term, bearing in mind
any operational limits imposed by the port authorities.

Section 3

Mooring Arrangements and Layouts

3.1 PRINCIPAL OBJECTIVES

The objective of a good shipboard mooring arrangement is to provide and arrange equipment to
accomplish the following:

• provide for a safe and efficient mooring pattern at conventional piers and sea islands, as

described in Section 1.

• facilitate safe and quick mooring, unmooring and line-tending operations with minimum

demand on manpower.

• enable safe and efficient mooring at anticipated non-conventional terminals such as

SPMs, MBMs and offshore terminals, including FPSOs and FSOs.

• facilitate safe and efficient handling of tugs when used for escort and harbour towing

activities.

• allow safe and efficient specific anticipated operations such as ship-to-ship transfers or

canal transits.

• provide for emergency situations such as excessive winds requiring doubling of lines,

emergency towing of disabled ships, or shipboard fires requiring the ship to be towed off
the berth quickly without shipboard assistance.

3.2 REQUIREMENTS AT PIERS AND SEA ISLANDS

The primary concern in the shipboard mooring arrangement is suitability for mooring at
conventional piers and sea islands, since this is the requirement most commonly encountered.
The principles for an efficient and safe mooring operation at these terminals are covered in
Section 1. These principles apply to ships of all sizes and may be summarised as follows:

• Mooring arrangements should be as symmetrical as possible about the mid-length of

the ship.

• For multi-directional environment, breast lines should be as perpendicular as possible to

the longitudinal center line of the ship.

• For directional environment (see Section 1.3) site-specific mooring patterns may be

considered to enhance lateral and/or longitudinal restraint.

• Spring lines should be as parallel as possible to the longitudinal centre line of the ship.

• Mooring lines in the same service should have about the same length between the ship's

winch and the jetty mooring points and should be of the same size and material.

In addition to the foregoing principles, the following general guidelines should be kept in mind in
laying out the shipboard mooring equipment:

• Keep mooring areas as clear as possible.

• Avoid tensioned mooring lines crossing areas in which personnel are normally working.

Section 3

• Locate mooring operations as far forward and aft as possible.

• Locate bow and stern chocks as far forward and aft and as low as possible.

• Locate spring line chocks as far forward and aft on the main deck as possible to provide

adequate line lengths to spring mooring points on the berth.

• Stress the need for correct alignment between chocks and fairleads and winch drums.

• Locate winch control positions to ensure a clear view of the mooring operations and the

officer-in-charge of mooring.

• Mooring lines in the same service should have about the same length between the ship's

winch and its chocks.

• All mooring lines should be capable of being run to either side of the ship.

3.2.1 Number, Size and Type of Lines

Before any mooring layout can be considered, the number, material and size of lines should be
determined. This can best be done by computer analysis. In determining the number, size and
type of lines, the following should be considered:

• Select the most appropriate material on the basis of strength, elasticity, durability and

handling characteristics. Section 6 provides general guidelines for the selection of
mooring line materials and line construction.

• Maximum flexibility is provided if all lines are of the same size and material (as

mentioned in Section 1.5). Ropes with low elasticity are recommended for larger ships as
they limit movement at the berth. High modulus synthetic fibre ropes are considered a
viable alternative to steel wire ropes.

• Moorings consisting entirely of high elasticity ropes are not recommended for larger ships

as they can allow excessive movement from strong wind or current forces, or through
interaction from passing ships. On smaller ships, a combination of synthetic ropes for
breast lines and spring lines of low elasticity is not uncommon.

• Where dynamic loading on moorings can be caused by swell conditions or by the close

passing of other ships, synthetic tails at the end of steel wire or high modulus synthetic
mooring lines may be used to provide additional elasticity. See Section 6.5.

• To increase the service life of moorings, the largest line that can safely be handled by

ship and terminal personnel should be selected. For wire rope, 44 mm diameter is
considered a working maximum based on operators' experience, although 48 mm
diameter wire ropes are used on occasion. For fibre rope, 80 mm diameter (10 inches in
circumference) is considered a practical maximum for ship-supplied hawsers. There are
practical minimums for the number of lines as given in the next paragraph, and there is
no need to select an MBL higher than required to comply with the number of breast and
spring lines determined by analysis.

• To provide a symmetrical arrangement about midships, breast and spring lines should

be of an even number. Four is considered a practical minimum for the number of spring
lines (to provide two lines in each direction). Likewise, four is a practical minimum for
breast lines to provide two lines each at the bow and the stern. If an uneven number of
breast lines is utilised, the decision on whether to deploy the extra line from bow or stern
should be determined by on-site analysis.

The considerations discussed above assume that mooring lines can be issued at either port
or starboard side of the ship and that all lines are permanently stowed on winch drums. If
the arrangement of winches and fairleads does not allow this, or the terminal or trading
pattern dictates otherwise, additional lines (and winches) would be required.

In addition to the recommendations on mooring line sizes and quantities listed above, the
designer as well as the ship operator should consider the generalised mooring equipment

Section 3

requirements stipulated by terminals. Sometimes these requirements are based on past
experience with inefficient mooring equipment (such as mixed material moorings) and may
demand more lines than required for a ship with efficient and well-maintained mooring
equipment. In such cases, the ship owner complying with the recommendations of this
Guide may strongly represent to the terminal operator that his ship provides an outfit able to
securely moor the ship in specific conditions, citing the Guide as grounds for its acceptance.

3.2.2 Arrangements for Breast Lines

Breast lines are effective in holding the ship against transverse forces; they also are most
effective in restraining the yawing tendency of a ship which is induced by wind, current, etc.,
acting on it. However, to be most effective in restraining the yawing tendency, issue points for
breast lines should be as far forward and aft as possible. The lead from the winch drum to the
shipside fairlead should be as direct as possible, preferably avoiding the use of pedestal
fairleads. If pedestal fairleads are used, the change in rope direction should be kept to a minimum
in order to reduce the loads on the fairlead. With limited deck space, a good arrangement can
often be accomplished by placing winches in a diagonal or transverse pattern as shown in Figure
3.1.

Details of typical mooring layouts for a tanker and a gas carrier are shown in the diagrams that
follow.

A point that should be considered is the shore lead of the lines issued at the extreme ends of the
ship. For instance, the aftermost two lines shown in Figure 3.4, which can be issued only from
chocks located at the transom, would chafe on the transom if the shore mooring dolphin is
forward of the transom. This is not very common, but occasionally occurs when a large ship
moors at a berth designed for smaller ships. The arrangements shown in the diagrams of typical
mooring patterns generally provide more flexibility in accommodating different shore mooring
point locations.

Some arrangements on ships in service may incorporate a 'first-line ashore'. This line is used
only to assist the ship during docking manoeuvres and is generally a polypropylene line because
of its buoyancy (refer to Section 6). An 80 mm diameter line of 370m length would be suitable for
large ships. Two such lines are provided, one forward and one aft. Several configurations are in
use to handle these lines. One is by use of powered twin grooved drums where the line is led
back and forth between the drums in a figure-of-eight fashion (this device can be compared to
bitts with powered barrels). The inboard end of the line is taken up by a powered stowage reel,
usually located below the weather deck. Another method is to use a conventional winch, and a
third method is to use a warping head of a winch in combination with a powered take-up reel.

There is no consensus among ship operators as to the need for 'first-line ashore' equipment, and
no special equipment is shown in the diagrams that follow.

If 'first-lines ashore' are used, they should not be counted in the mooring restraint requirements
given in Section 2 unless they are of the same material as the other mooring lines and mounted
on drums equipped with brakes as recommended in Section 7.

3.2.3 Arrangements for Spring Lines

In order to provide an efficient lead to the terminal bollards, spring line issue points should be as
far forward and as far aft as possible. To avoid line chafing on the shell, the issue points must
also be within the parallel body. In practical terms, this means that the shipside chocks serving
the forward headsprings should be at the point where the upper deck starts to taper into the bow
area. The shipside chocks serving the aft backsprings are normally just forward of the aft
accommodation house where a direct lead to the winch can be provided. This arrangement
results in the aft spring winches and the winches serving the aft breast lines being too far apart
for efficient manning during docking and undocking. To overcome this, at least one owner has
attempted to locate the aft spring winches on the aft deck as shown in Figure 3.4. However, in
the example shown, the shipside chocks are aft of the parallel side area, which can result in line
chafing at some terminals. Nevertheless, with proper coordination of hull shape and mooring
arrangement at the early design stage, this concept may be workable and could contribute to
reduced manning requirements.

Section 3

FIGU

TYPI

CAL

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NGE

T OF

A T

mod

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to sh

mmetr

ical moor

g arr

ang

ement, lo

leads

r sp

bow

stopp

s align

ed, etc

Section 3

3.3 REQUIREMENTS AT SPMs

The required fittings for mooring to an SPM are described in Reference 1 ("Recommendations
for Equipment Employed in the Bow Mooring of Conventional Tankers at Single Point
Moorings".) The fitting requirements from Reference 1 are reproduced in Appendix E. The
design of fittings in accordance with Appendix E will ensure adherence to OCIMF's
recommendations for SPM mooring, and is therefore recommended. Special attention should
also be paid to the requirements of specific SPM operators. Cases are known where ships of
less than 150,000 DWT have been rejected due to lack of a second stopper, although current
OCIMF recommendations require this only for ships over 150,000 DWT.

Appendix F provides details of a study undertaken to determine the stress in chain when
tensioned over a curved surface. This is relevant when considering chafing chain on SPM
hawsers being passed through a chock and being led to the bow stopper. The results of the
study serve to confirm that adherence to the recommended equipment arrangements, as
detailed in Appendix E and Reference 1, should not result in a significant reduction in the
breaking strength of the chain.

The recommendations in Reference 1 also apply when the SPM mooring equipment is used to
moor conventional tankers in tandem at FPSO/FSO terminals.

3.4 REQUIREMENTS FOR EMERGENCY TOWING,

ESCORTING AND PULL-BACK

Regulation Ch V/15-1 (Ch II-1/3-4 from 1/7/98) of SOLAS adopted by IMO in 1994, contains the
following provisions:

• All "tankers" of 20,000 DWT and above are to be provided with an emergency towing

arrangement at both ends.

• The term "tankers" includes oil tankers, chemical tankers and gas carriers.

• The minimum components for an emergency towing arrangement are to comprise of the

following:

Component Forward

Aft

Towing pennant

Optional

Required

Pick-up gear

Optional

Required

Chafing gear

Required

Dependent on design

Fairlead

Required

Strong point

Required

Roller pedestal lead

Required

Dependent on design

• The forward arrangement of strong point, fairlead, chafing gear and roller pedestal lead

reflects the guidance previously contained in IMO Assembly Resolution A.535(13),
which on many oil tankers, may be accommodated by the fittings recommended to
facilitate mooring at SPM's (see Appendix E).

• The arrangement aft contains a major new provision introduced since IMO Assembly

Resolution A.535(13) was developed, namely the requirement for the ship to carry a pre-
rigged towing pennant incorporating pick-up gear. The pick-up gear must be capable of
being deployed manually by one person and the pennant must be demonstrated to be

Section 3

• Towing arrangements to be adequate for towing line angles up to 90° from the ship's

centreline to both starboard and port in the horizontal plane and to 30° below horizontal in
the vertical plane.

• The chock to be located on the stern, as close as possible to the centreline of the ship. (If

the emergency towing arrangement is used, the strong point should be located so as to
facilitate towing from either side of the stern and to minimise the stress on the towing
system - see Resolution MSC.35(63)).

• The chock opening to be oval or to have well-rounded corners.

• The towing or connection point to be aligned longitudinally with the chock and clear of all

obstructions.

• The chock to have a minimum diameter of 600 mm and a minimum height of 300 mm.

• The minimum distance from strong point to chock to be 4.0 metres. It is recognised that

this may be difficult to achieve on ships of less than 50,000 DWT but is aimed at ensuring
that the eye splice of the towing line sits inboard of the chock. If the distance from strong
point to chock is less than 4.0 metres, the tug should be advised accordingly. (This
recommendation does not apply if the emergency towing arrangement is used as, in that
case, the chafing gear will lie in the chock).

• Each fitting to be clearly marked by bead weld outline with its SWL. The SWL to be

expressed in metric tonnes (letter 't') to avoid any confusion.

• Fixed gear such as strong points, chocks, foundations and associated supporting

structure to be demonstrated as adequate for the loads imposed. The ship should hold a
copy of the manufacturer's type test certificate for the fittings or a certificate confirming
that the fittings are constructed in strict compliance with a recognised standard that
specifies design load, safety factor and load application. The ship should also hold a
certificate attesting to the strength of the strong points, chocks, foundations and
associated supporting structure substantiated by detailed engineering analysis or
calculations and an inspection of the installation. Both certificates should be issued by
an independent authority (such as a Classification Society).

The equipment should be subject to periodic survey and be maintained in good order.

• Means to be provided for safely letting go the tug in the worst case environmental

conditions likely to be experienced while the tug is attached. When letting go, the towline
should be slacked back to the chock in a controlled manner, using a messenger line if
necessary, to avoid whiplash.

• The equipment to be used for the guidance and connection of the tug's towing line to be

clearly marked as such and preferably painted a distinctive colour.

The recommended dimensions for the chock (600 mm x 300 mm) take into account the increased
use of high modulus synthetic fibre ropes as towing lines for escort duties. The minimum bending
diameter for such ropes is typically 10 times the rope diameter for plaited lines and 8 times the
rope diameter for braided lines. The diameter for a plaited grommet with a minimum breaking
load (MBL) of 480 tonnes is typically 68 mm. This gives a minimum bending diameter of 680 mm
and leads to the conclusion that a minimum diameter of 600 mm is appropriate for an escort/ pull-
back service with an MBL of 400 tonnes. The recommended height of 300 mm is sufficient to
accommodate the towing line/ grommet with possible protection against chafing.

High modulus synthetic fibre ropes are susceptible to damage by cutting and abrasion. Fittings
that are also used with wires may have gouges and sharp edges that could damage such ropes
unless steps are taken to protect them. It is recommended that chocks and strong points are kept
fair on the contact surfaces to avoid undue abrasion of tow lines.

Certification of equipment to demonstrate adequacy for the anticipated loads is regarded as a
‘one-off’ exercise. Assuming there are no changes to the fittings or their supporting structure, re-
certification should not be necessary.

Section 3

3.5 REQUIREMENTS FOR MULTI-BUOY MOORINGS

Multi-buoy mooring (MBM) consists of tying up a ship to several permanently anchored buoys in
conjunction with the ship's own anchors. It is also called conventional buoy mooring or 'CBM'. A
typical five-buoy configuration is shown in Figure 3.10. In some cases the ship is moored to
buoys only without the use of the ship’s anchors. This type of berth is an ’all buoy berth’ or ‘ABB’.
ABB’s are generally located where seabed conditions prevent the effective use of the ship’s
anchors or where additional mooring restraint is needed for the anticipated environmental
conditions.

Multi-buoy moorings are usually located in areas where weather and sea conditions are mild to
moderate. This is because the mooring restraint is limited due to the requirement to payout the
mooring lines on both port and starboard sides, in contrast to mooring at piers and sea islands
where the lines are paid out on one side only.

The standard mooring equipment will be adequate in most cases where the ship is equipped in
compliance with these Guidelines. Nevertheless, the following points should be noted:

(a) The terminal will normally require the ship to provide the necessary mooring equipment. Two

or three lines may be required to be run out to all or some of the buoys.

Some terminals may utilise the aft spring lines (for beam moorings), which are generally
issued from chocks forward of the deck house (contrary to Figure 3.10 where all lines are
issued from the aft deck). This will free all lines on the aft deck for use on the quarter and
stern buoys.

(b) Adequate chocks at the transom should be provided to facilitate mooring to the stern buoy.

although many MBM’s require synthetic or high modulus fibre ropes for handling purposes
and to better manage the dynamic forces in the mooring. The design of the mooring system
has a major influence on the mooring loads and the most important parameters are those that
affect the elasticity or stiffness of the system. A very stiff mooring system will severely
constrain the response of the ship to waves, resulting in very high loads on the mooring as it
approaches the limits of the system’s elasticity.

(d) Some berths provide 'preventer wires', or 'shore wires', which are permanently attached to

the buoy and are towed to the ship with a launch. Handling and securing such wires to a
ship's bitts can be difficult. This is because the wires are relatively long and must be pre-
tensioned to prevent drift. One method of pre-tensioning shore wires is by use of an existing
ship's winch, first removing the dedicated synthetic or wire rope from the winch, and then
reeving the shore wire in its place. It should be noted that if the shore wire is left in tension on
the winch, the holding power will be governed by the winch brake and not the strength of the
shore wire. To fully utilise the shore wire strength after pre-tensioning on the winch, the wire
should be transferred to a suitable set of bitts using a chain or carpenter's stopper. The use of
the preventer wire by the shore may often require the ship to deploy a mooring line of similar
material and elasticity to the buoy in order to ensure an equal distribution of forces between
the lines.

Section 3

heaving line onto the warping head of a mooring winch or, on some larger ships, the provision of
dedicated capstans in way of the bitts.

In determining chock locations, the following points should be considered:

• Adequate separation of chocks should be provided to allow manoeuvring space for tugs.

For large tugs, handling VLCCs or ULCCs, this separation should be about 50 to 60
metres.

• Chock locations should be in the same transverse plane as tug-pushing locations, as

tugs may alternately push or pull from the same location to check the ship's motion. The
forward and aft chocks should be placed so that maximum leverage is provided for
turning the ship, but not be so far towards the ends of the ship that the flare of the hull
endangers the tug during pushing operations. It should also be noted that the tug push
(and consequently chock) location is normally near a transverse bulkhead or web frame,
as determined and marked by the shipyard or, in the case of retrofitting, by naval
architect’s design analysis.

• An alternate neutral pull or push location is required midships to allow checking the

lateral motion without applying a turning moment. The chock is generally located just aft
of the hose saddle.

• Towing arrangements should be adequate for towing line angles over a 180° arc in the

horizontal plane and 0° to 90° downwards in the vertical plane, outboard of the chock.

For VLCCs and ULCCs, the above requirements generally result in five push/pull locations on
each side of the ship. For smaller ships, where adequate separation of five tugs cannot be
provided, three locations on each side will suffice.

Means for safely letting go the tug should be provided. When letting go, the towline should be
slacked back to the chock in a controlled manner, using a messenger line if necessary to avoid
whiplash.

Bitts and chocks used for guiding and attaching tug's lines are to have minimum SWLs, when
used with a single eye towing line or grommet, in accordance with the following table:

Maximum rope loading

Ship Size

in tonnes -

Nominal Size of

Attached with Eye

Bitt (D) in mm

(Figure-of-Eight Belayed)

20,000 - 49,999 DWT

64 (32)

400

50,000 DWT and above

92 (46)

500

Note:

(1) "Figure-of-Eight" values are the values recommended to be marked on the fitting as the
SWL

Each fitting that is intended for use with tugs is to be clearly marked by bead weld outline with its
SWL. The SWL should be expressed in metric tonnes (letter 't') to avoid any confusion.

For bitts, the SWL marked on the bitts should be the maximum permissible when using a wire or
a rope belayed in a figure of eight near the base of the bitts (see Section 4.4.1). When using a
single eye, this SWL can be doubled, i.e. the permissible SWL using a single eye is then twice
the SWL marked on the bitts.

The SWL of ship's equipment used for connecting emergency towing-off pennants (fire wires)
should be brought to the attention of the terminal representative when completing the Ship/Shore
Safety Check-List.

Section 3

Fixed gear such as strong points, chocks, foundations and associated supporting structure
should be demonstrated as being adequate for the potential loads. The ship should hold a copy
of the manufacturer's type test certificate for the fittings or a certificate confirming that the fittings
are constructed in strict compliance with a recognised standard that specifies design load, safety
factor and load application. The ship should also hold a certificate attesting to the strength of the
strong points, chocks, foundations and associated supporting structure substantiated by detailed
engineering analysis or calculations and an inspection of the installation. Both certificates should
be issued by an independent authority (such as a Classification Society).

Certification of equipment to demonstrate adequacy for the anticipated loads is regarded as a
‘one-off’ exercise. Assuming there are no changes to the fittings or their support structure, re-
certification should not be necessary.

3.7 REQUIREMENTS FOR BARGE MOORING

In many cases, barges can be moored with fittings provided for other mooring requirements.
Nonetheless, some VLCCs and ULCCs lack suitable fittings for mooring a barge alongside the
midships manifold or the aft fuel oil manifold. In this case, it is recommended that a set of closed
chocks and bitts be provided, port and starboard, about 35 metres forward and aft of the midships
manifold and, where appropriate, the aft bunkering station.

3.8 REQUIREMENTS FOR CANAL TRANSIT

Special fittings may be required for transit through canals. The best known requirements are
those for the Panama Canal where ships are kept in position in the locks by shoreside
locomotives having their own mooring lines mounted on winches. Ships suitable for transit
through the Panama Canal should comply with the detailed local regulations.

3.9

REQUIREMENTS FOR SHIP- TO-SHIP

(STS) TRANSFER

Ship-to-ship transfer normally requires the mooring alongside offshore of two different size ships
for the purpose of cargo transfer. The mooring arrangements adopted will depend upon the sizes
of the ships carrying out the operations and the difference between their sizes. As a general
guideline, Figure 3.11, taken from Reference 3, illustrates a recommended and proven mooring
arrangement for a transfer operation in offshore waters. A prime consideration in mooring during
STS operations is to provide closed chocks for all lines without the possibility of chafing against
each other, the ships or the fenders. This is critical in view of the large relative freeboard changes
between the ships.

Section 3

It is recommended that the fairleads are of the enclosed type, since the relative freeboard
between the two ships will change significantly during the STS transfer operation. If the lines are
of wire rope, the opening of the closed chocks must be large enough to permit easy passage of
the special shackle connecting the tail to the wire rope.

3.9.2 Requirements for Discharge Ship

The discharge ship, which is generally the larger ship, may require special mooring fittings to
allow a proper mooring pattern. Since industry practice is to use the starboard manifold of the
discharge ship, special fittings are generally provided on the starboard side only. As can be seen
in Figure 3.11, the off taker's spring lines terminate on the discharge ship in a location not usually
fitted with chocks. For this reason it is recommended that tankers over 160,000 DWT be fitted
with two additional sets of heavy duty closed chocks with clear openings of 500 x 400 mm
positioned on the starboard side of the ship. These chocks should be located 35 metres forward
and aft of the center of the manifold, or as close to this position as possible. All chocks
associated with ship-to-ship transfers should be smoothly finished both inboard and outboard to
prevent chafing.

Tankers of less than 160,000 DWT likely to be involved as a discharge ship in STS operations
should be provided with mooring bitts and chocks, of a size similar to other mooring fittings, at a
suitable distance from the manifold to receive the offtaker's spring lines.

The recommended minimum number of closed chocks on the starboard side for STS operations
is three aft and four forward.

The aft closed chocks should be located as far aft as practicable and the forward closed chocks
should be located on, or to starboard of, the centre line and clear of any protruding anchor
housings.

Each designated STS suitable closed chock should be accompanied by bitts capable of taking at
least two mooring lines and rated to at least the same SWL as the chock.

Similarly to requirements for the offtaker, the discharge ship's mooring chocks should all be of the
closed type to avoid difficulties caused by the large relative changes in freeboard. The require-
ments for closed chocks of adequate size for breast, head and stern lines may already be met by
requirements in these Guidelines for mooring at piers and sea islands, and by tug handling
provisions. But in other cases - especially on ships where closed chocks are not used for the
standard mooring lines - special STS transfer closed chocks may be required on the starboard
side. In any event, suitable bitts are required inboard of the closed chocks for securing the off-
taker's mooring line. Some operators allow only one line to be used in each chock to reduce the
possibility of line chafing with changing ship draughts. In this case closed chocks are arranged in
pairs and served by a common set of bitts. Further, it is recommended that means be provided
for passing a messenger line (attached to the eye of the offtaker's mooring line) through the
chock and onto the warping head of a mooring winch. For this purpose, a bitt or guide post may
be used in lieu of a pedestal roller fairlead.

Further information on all aspects of STS transfer operations may be found in Reference 3.

3.10 ARRANGEMENTS AT CARGO MANIFOLDS

Deck fittings in the manifold area of oil tankers are provided in accordance with the OCIMF
publication 'Recommendations for Oil Tanker Manifolds and Associated Equipment' (Reference
2). These fittings will include cruciform bollards, closed chocks and mooring bitts that are
intended to facilitate the hoisting and hanging of cargo hoses at sea berths.

It is emphasised that the fittings provided at the manifold in accordance with the OCIMF
recommendations are not intended for mooring activities and should not be used for this purpose.

Section 3

3.11 MOORING AUGMENTATION

IN EXCEPTIONAL CONDITIONS

As mentioned in Section 2, it would not be practical to design all ships for the worst possible
operating environment. Where the Standard Environmental Criteria are exceeded, the ship
should either leave the berth, obtain continuous tug assistance or arrange for additional mooring
restraint.

The ship and terminal should also be prepared to take appropriate action in other emergencies,
such as fires, and this may require additional equipment aboard the ship.

3.11.1 Provision of Shore Moorings

To augment the mooring system when conditions exceed the Standard Environmental Criteria,
shore moorings may be provided. In order to receive these moorings on board, it is
recommended to provide closed chocks, associated bitts and warping ends for a number of
additional lines equal to at least 50% of the ship's standard mooring lines. The chocks will usually
be located next to the fairleads for the standard mooring lines.

This allows heaving aboard of the shore lines via heaving lines led to warping heads of mooring
winches. The strength of fairleads and bitts should be based on the MBL of the ship's standard
mooring lines.

3.11.2 Use of Shore-Based Pulley

Another method of providing additional mooring restraint is to use a shore-based pulley system
around which the ship's mooring line is led and made fast back on board the ship. In its simplest
form the shore fitting could consist of a bollard of a sufficient diameter for the size of wire to be
employed. A minimum ratio of bollard/wire diameter of 12:1 should be employed.

The provision of a revolving bollard or pulley wheel is recommended to reduce friction on the wire
and to ensure that when moorings are adjusted the tension in each part is readily equalised. To
provide a release facility under normal operational conditions, the pulley should be incorporated
on a quick release mounting so that on the activation of the release mechanism the pulley
capsizes and the bight of the wire is released and thrown clear of the jetty. This equipment is
available from manufacturers of conventional quick release hooks. The pulley must be designed
properly to prevent it from releasing the line inadvertently due to the pulley's weight. In
considering the design specifications for this equipment it should be remembered that loads sus-
tained will be approximately twice that experienced by a mooring hook or bollard to which a single
wire is attached.

A suitable heavy duty winch or capstan should be provided to assist in heaving the bight of the
wire on to the fixed mooring structure and securing it over the pulley or bollard.

3.11.3 Advantage of Pulley System

The principal advantage of this equipment is that all moorings can be properly tensioned by the
ship's mooring winches in the normal way and manual handling of heavy wires on board is
reduced. Also the problem arising from divided control, which can occur with the use of shore
wires on winches, is avoided.

While the use of such a system will reduce the load in a ship's moorings in proportion to the
number of pulleys provided, its complete effectiveness depends on a ship's mooring equipment
being in good condition initially, as with all mooring systems. The terminal should evaluate the
effect that ship's tails would have on the loads induced in the mooring lines. Since now there is
only one tail effectively for two lines, the elasticity of each is decreased.

3.11.4 Disadvantage of Pulley System

The principal disadvantage of this system is the difficulty of handling the length of wire involved
by using the bight, particularly at marginal jetties where moorings may have long drifts. In
addition care should be exercised to prevent abrasion of the tails when they come back aboard
the ship. Since the tail will usually be in the fairlead when the line is secured, the tail can abrade,

Section 3

especially if the fairlead is not smooth or free of burrs.

To avoid abrasions, some terminals take the tail end to a more distant ship's bitt and others
shorten the tail by belaying around the bitt. Both of these affect the elasticity of the system and
must be considered when calculating restraint capacity.

Larger mooring boats may also be necessary to adequately handle heavy bights associated with
this system.

3.12 EMERGENCY TOWING-OFF PENNANTS

Terminals often require the provision of so-called ‘emergency towing-off pennants’ or 'fire-wires'
when tankers are moored alongside. These are lines hung over the off-berth side of the ship.
They enable tugs to pull the ship away from the pier without the assistance of any crew member
in case of a serious fire or explosion. Refer also to Reference 4 ("International Safety Guide for
Oil Tankers and Terminals").

The requirements for emergency towing-off pennants should be subjected to review and risk
analysis by terminals to determine whether or not there should be a routine requirement for ships
to rig them. Among factors that should be considered are the following:

• Are towing-off pennants really necessary and what is the possibility of them being used?

• Do the terminal’s emergency procedures require a ship to be removed from the berth if it

is immobilised by fire?

• Is it possible to release the ship’s moorings to permit the ship to be removed from the

berth?

• How long will it take for tugs to be mobilised?

• Could the deployment of emergency towing-off pennants compromise security

arrangements for the ship and terminal?

If required, emergency towing-off pennants are commonly provided at the offshore bow and
quarter. If required at a buoy mooring, the wires will be rigged on the opposite side to the hose
string. In order to facilitate emergency release of the wires, they should be secured to bitts with a
minimum of five turns and be led directly to a shipside chock with no slack on deck. The
outboard end of the line is provided with an eye to which a heaving line is attached and led back
to the deck. During loading or discharge, the heaving line is periodically adjusted to maintain the
eye of the emergency towing-off pennant one to two metres above the water as shown in Figure
3.12. Some terminals require different methods and operators should be aware of local
regulations.

Section 3

DWT

MBL

Length

Less than 20,000

30 tonnes

25 m

20-100,000

55 tonnes

45 m

100-300,000

100 tonnes

60 m

300,000+

120 tonnes

70 m

TABLE 3.1 EMERGENCY TOWING-OFF PENNANTS – RECOMMENDED MBL AND LENGTH

Emergency towing-off pennants should not be attached to a set of bitts with a Safe Working Load
that is less than the Minimum Breaking Load of the pennant. It should be noted that for bitts
(double bollards) the SWL marked on the bitts should be the maximum allowed when using a wire
or rope belayed in a figure of eight near the base of the bitts. This will be half the maximum
permissible SWL when a single eye is placed over one post.

3.13 COMBINATION OF VARIOUS REQUIREMENTS

The requirement for fittings set forth in Sections 3.2 (piers), 3.3 (SPMs), 3.4 (emergency towing,
escorting and pull-back), 3.5 (MBMs), 3.6 (harbour towing), 3.7 (barge mooring), 3.8 (canal
transit), and 3.9 (STS transfer) do not apply simultaneously. In the interest of reducing cost and
complexity, it is desirable during the ship design stage to adjust the location of shipside chocks
slightly so that one chock or set of bitts can serve several requirements. At the same time, all
possible line leads for the various requirements should be considered. For instance, when a
shipside fairlead designed primarily for use at piers and sea islands in conjunction with mooring
winches is utilised for requirements 3.4, 3.5, 3.6, 3.7 or 3.8 or 3.9, measures may be necessary
at the inboard edge if roller fairleads are used. This is especially acute for universal roller
fairleads, since the inboard fore and aft leads are restricted by the end frames.

3.14 SAFETY AND OPERATIONAL CONSIDERATIONS

For safety reasons, it is highly desirable to lead mooring lines from winch drums directly to the
shipside chock. If the use of pedestal fairleads cannot be avoided, the winch controls should be
located to minimise risk to the operator.

In the interest of manpower savings and speedy mooring and unmooring operations, all mooring
lines should be stowed on drums and consideration given to the provision of winches that have
an individual drive for each drum with no need for clutching and de-clutching. This will eliminate
the often difficult task of clutching and declutching drums from a common drive shaft in
combination with setting and releasing drum brakes.

3.15 EQUIPMENT AND FITTING LINE-UP

Mooring fittings require adequate clearance for routine operations, and winches have to be
arranged to provide an adequate fleet angle for the drum. This is the maximum angle the line
deviates from a direction perpendicular to the drum axis. The following are some 'rule-of-thumb'
guidelines.

The minimum distance between a fairlead and bitts should be 1.8 metres in order to provide
adequate space for the application of rope stoppers (see Figure 8.6 for stopper use).

The minimum distance between a winch drum and the nearest fairlead or chock should be such
that the fleet angle does not exceed 1.5°. This means that the minimum distance to the nearest

Section 4

Design Loads, Safety Factors

and Strength

4.1 GENERAL

These guidelines are intended to assist ship operators, designers and equipment suppliers in
outfitting ships with mooring equipment designed to accommodate the expected loads safely.

“Mooring equipment” means those pieces of equipment mounted onboard a ship to handle the
loads needed to attach the ship temporarily to a berth, or to another ship. Mooring equipment
includes bitts, mooring winches, chain stoppers, fairleads, chocks and capstans. Anchoring
equipment is not included in these guidelines, since its specification is adequately covered in
Classification Society rules.

In order to determine the required design strength of a particular fitting or piece of mooring
equipment, the following information is needed:

• the magnitude of the greatest possible tension in the line that can contact the fitting. In

these Guidelines, the design value of this line tension is defined by, and shall be equal
to, the Minimum Breaking Load (MBL) of the line. The Safe Working Load (SWL) that will
be marked on the fitting is then normally equal to the MBL.

• the magnitude, position and direction of application of the most severe load that can be

applied to the fitting in service. The force given by this calculation is called the Design
Basis Load (DBL). Its calculation takes account of the location and geometry of the line
as it contacts the fitting and is based on a force in the line equal to the MBL. For
example, a line led 180º around a bollard subjects the fitting to a force (equal to twice the
rope MBL) that acts on the bollard midway between the two legs of rope, while a line
attached to a bollard near the top of the barrel produces a higher stress than one
attached close to the base

• the safety factor required by these Guidelines. This is specified on the stresses caused

in the fitting by the DBL. It provides a margin of safety against the permanent
deformation (yield) of any part of the fitting or its attachments to the ship.

It is worth repeating that in these Guidelines the SWL is defined by the MBL of the line, and not
by the force exerted on the fitting by the line. Further, it is the SWL of the fitting rather than a safe
working load for the line. At the SWL of a fitting, the line is at its MBL. As defined, the SWL is
approximately twice the maximum force in the line in normal service (see the line safety factors in
Section 6.1.2). It is a tension that will only be reached in rare and extraordinary circumstances.
Indeed, in everyday service the line tension is unlikely to be more than 20% of MBL.

Safety factors generally account for uncertainties such as additional dynamic loads, normal wear
or corrosion of fittings or equipment, small material or welding defects, locked-in weld stress, and
for uncertainties in the design calculation model used. The value of the safety factor is also
influenced by the consequences of a failure. As an example from another area, very high safety
factors are used on lifting gear, particularly if it is used to hoist personnel. On the other hand,
safety factors generally are also influenced by the probability of the design event occurring, with
rare events requiring lower safety factors than everyday occurrences. It is noted here that the
probability of a given fitting experiencing the forces associated with line breakage once during
the life of a ship is small. This low probability suggests that the possibility that some localised
yield might occur in the fitting, (for example, because actual rope strength exceeds the MBL

Section 4

particularly early in the life of HMPE ropes) during this design event should be acceptable.

As a significant change from the previous edition of these Guidelines, the safety factor no longer
incorporates an allowance for any geometric effects that would give a factor on the service
tension in the line in calculating the force applied to a fitting, e.g., the factor of two on the line
tension that arises in calculating the force applied to a bollard carrying a 180

wrap. Instead, a

separate geometric factor is specified. This change brings these guidelines into line with the
practice in many other design codes.

The “Design Basis Load” of the fitting is then given by the product of the Minimum
Breaking Load and the geometric factor. The dimensions of the fitting should be chosen
by the designer so that the stresses caused by the Design Basis Load acting on the fitting
nowhere exceed a percentage, in most cases 85%, of the specified minimum yield stress
(SMYS) of the material. Thus, the safety margin against yield is the reciprocal of 0.85, i.e
1.18.

4.2 BASIC STRENGTH PHILOSOPHY

Since a wire rope, synthetic rope or chain with a specific minimum breaking strength is used as
the link between the ship and the berth, it is very desirable to relate the required strength of
equipment and fittings to the strength of the associated lines or chains.

Industry practice has not been consistent in this respect. Some designers have based the
strength of fittings and equipment on the maximum line tension anticipated for certain weather
criteria; others base the ultimate (breaking) strength of fittings and equipment on the minimum
breaking load of the mooring line. Neither of these possible strength criteria is appropriate if
damage to the fitting and equipment is to be avoided, simply because under heavy loads it would
be possible for the fitting to become damaged while the mooring line was still intact.

The consequences of damage to fittings and equipment are usually more serious and costly than
those of damaging or breaking a line.

The recommended design basis for mooring fittings and equipment is therefore that the
fitting or piece of equipment and its components should be able to withstand, without
permanent deformation, the design basis load (DBL) given by multiplying the mooring line
manufacturer’s minimum break load (MBL) by the geometric factor specified in these
guidelines. The magnitude, point, and line of application of this load on the fitting should
take due regard of the line geometry. “Permanent deformation” is to be avoided by
limiting the calculated stresses caused by the DBL to a percentage, in most cases 85%, of
the specified minimum yield stress of the material.

This general requirement should be modified if it is possible that more than one line may be
deployed on a fitting. For example, it may be possible to pass two lines through a single fairlead.
If, in this case, the effects of the two lines are additive, the design basis load must be increased
to allow for this possibility.

It is specifically recommended that winch brake rendering (slippage) in a mooring should not be
used to reduce the DBL below the value given above. Brake rendering at specific loads cannot
be guaranteed, as brake settings are not precise and, indeed, winches may inadvertently be left
engaged in gear. Rather, brake rendering is considered to be an additional safety mechanism in
protecting the integrity of the mooring system against unexpected failure when the ship is
moored at a terminal.

It is further noted that rope over-strength, including the modest excess of strength in new ropes
above their MBL and the increase in pure tensile strength in HMPE ropes in the early part of their
working lives, need not be considered in calculating the DBL. (Appendix B refers).

Section 4

4.3 EXISTING STANDARDS AND REQUIREMENTS

Numerous national standards for mooring fittings exist, but often they do not provide sufficient
information to establish the actual strength. In some cases, a 'SWL' is stated, but no safety
factor; in others an 'applicable line' is listed, but no information as to how the line stress relates to
fitting stress is given. In yet other cases, the line position, direction or quantity may be missing. In
comparing two fittings designed to different standards, it is possible that the obviously weaker
design lists a higher rated 'load'. Listed 'load' variations between two fittings of equal size may be
as much as a ratio of 1 to 10, most of which can be due to different definitions of 'load', safety
factors and load application.

Mooring fittings are also often specified in nominal sizes, such as 300 mm or 400 mm diameter
bitts. Fittings with the same nominal size manufactured to different standards may have very
different actual strength capabilities and safety factors.

When the applicable mooring line size is determined from the existing standards, it is
recommended to check the allowable minimum breaking load (MBL) of the rope, if specified,
along with the specified applicable rope size, because the rope breaking strengths may be
different among standards and dependent on the grade. It should be noted that rope
manufacturers catalogue minimum breaking strengths using different methods, for example, ISO
shows MBL as unspliced strength, whereas USA manufacturer’s standards use spliced strength.
In addition, some manufacturers catalogue average minimum break strength, whereas others
use 2 standard deviations below lowest actual break strength. This can result in significant
variations above catalogue strengths when new. For the purposes of these Guidelines, the ISO
definition of MBL is considered applicable.

As a general point, it is not recommended that any design proceeds on the basis of selecting a
mixture of clauses and factors from different standards.

More positively, MSC Circular 1175 and IACS UR A2 include mandatory minimum requirements
for mooring fittings and supporting hull structure, and reference international standards in force.
The recommendations given in this Section are intended to match or exceed these mandatory
requirements. In addition, the principle that the supporting deck structure should be at least as
strong as the fitting has been recognised.

As one example, Table 4.1 compares the recommendations given in Section 4.4 of these
Guidelines with the requirements of MSC Circular 1175.

Rope

MBL

(tonnes)

Fitting

SWL

(tonnes)

Design Load at

Geometric

Factor of 1.0

(tonnes)

Max. Fitting

Stress at SWL

(% of yield)

Max. Supporting

Hull Structure

Stress at SWL

(% of yield)

Section 4.4

100

80% of SMYS

(see Section 5)

MSC Circ
1175

100 100

125

References

industry

standards

80% (i.e. 100% at

design load)

TABLE 4.1: COMPARISON BETWEEN SECTION 4.4 AND MSC CIRC 1175

Section 4

4.4 RECOMMENDED DESIGN CRITERIA

Until accepted international standards are developed for all mooring equipment, safety factors
and DBL and SWL values should be set as given in this Section. These recommendations are
based on the basic strength criteria mentioned above and allow for wear and tear or corrosion in
service, residual stresses or construction defects during manufacture and a degree of dynamic
loading of the fitting.

If fittings are being regularly exposed to dynamic loadings, then dynamic analysis should be
used to identify the true peak loading. A separate consideration of fatigue damage may then be
necessary.

If fittings are to be exposed to low air temperatures in service, then steel with appropriate low
temperature properties should be employed for the fittings and their supporting structures.

As indicated in Section 4.2, the basic recommendation for any fitting is that the fitting or
equipment should not suffer any permanent deformation when the associated line is tensioned to
its MBL. The marked SWL should equal the MBL. This requirement is achieved by ensuring that
the stresses in the fitting do not exceed a percentage, in most cases 85%, of yield when the
fitting is subjected to an applied design basis load (DBL) given by rope MBL times the
appropriate geometric factors given later in this Section.

In a Finite Element Analysis, the stresses may often exceed yield in some localised hot-spots
due to abrupt geometrical changes, constraints and load introductions. Such local areas of high
stress should be accepted for ductile materials where stresses will re-distribute without affecting
the safety of the structure.

This general requirement is modified if it is possible that more than one line may be deployed on
a fitting. For example, it may be possible to pass two lines through a single fairlead. If, in this
case, the effects of the two lines are additive, the design basis load must be increased to allow
for this possibility. Otherwise, the worst loading applied by either of the two lines separately
should be considered. The marked SWL should be the MBL of one line and the acceptability of
more than one line on the fitting should be indicated on the mooring layout plan described in
Section 4.6.

When selecting mooring equipment for new ships or conversions, it is recommended that the
strength criteria listed in this Section be specified in addition to the usual information on size and
materials. Reference to another specific standard should only be made if all strength details are
published and are in general agreement with the recommendations in Section 4.4. Standard
fittings of unknown strength may be specified with the proviso that the standards are to be used
as a guide to overall dimensions, materials and design concept, but that actual scantlings should
be modified, if necessary, to meet the strength recommendations in Section 4.4. In this case,
compliance with the criteria should be substantiated with detailed calculations and a load test for
each generic type of fitting.

The capacity of the foundations and supporting deck structure to any fitting must be specifically
considered when rating the capacity of any fitting. As a basic principle, the strength of the
supporting structure and the connection of the fitting to it should be greater than the marked
SWL of the fitting itself, so that any fitting failure does not result in damage to the structure of the
ship itself (see Section 5).

In the guidance that follows, the geometric factors, which as indicated in Section 4.1 allow for the
geometry of the contact between line and fitting, can in principle be directly related to the angle
through which the line is deflected in its passage through or over the fitting. If this “wrap angle” is
defined as

θ, then the theoretical geometric factor (GF) is:

)

sin(

… (Equation 4.1)

For a wrap angle of 180

this produces a geometric factor of 2.0. Other wrap angles permit a

smaller factor, including values less than 1.0 for small wrap angles. Hence

θ may be taken

conservatively as 180

, but this will adversely affect economy for small values of

θ. On the other

Section 4

hand, if equation 4.1 is employed, it is absolutely essential that the value of

θ used should be the

largest deflection angle that can occur at that fitting having due regard to all possible present
and future rigging arrangements on the ship, and to combining vertical and horizontal deflection
angles. In practice, designers may conclude that the conservative value, 2.0, should be
generally employed.

For the benefit of designers familiar with the 1997 (2

) edition of Mooring Equipment Guidelines,

it is noted that the safety factor of 2.36 that was referenced in several sections combined a
geometric factor of 2.00 and a safety factor on yield of 85%, expressed as its reciprocal, 1.18,
resulting in the product of those two factors, namely, 2.36.

4.4.1 Bitts (Double Bollards)

Fitting Diagram

Geometric

Factor

Load Position

Marked

SWL of

Fitting

Design

Basis Load

Stress

Limit

(see

4.4.11)

Test

Load

Bitts
(Double
Bollard)

GF= 2.00

1.2D above
base of a bitt
of diameter
'D'

MBL DBL=

MBL x GF

85% of

SMYS

DBL

As an example, if the rope MBL is 100 tonnes, the DBL is given by:

DBL = 100 x 2.00 = 200 tonnes

and the stresses caused by this DBL should be

≤ 85% of the specified minimum yield stress

(SMYS).

It is essential to understand that bitts belayed in figure-of-eight style can subject either of the two
posts (barrels) to a force at least twice as large as that in the mooring line. Indeed, if for any
reason there is a low friction coefficient between line and bitts, due for example, to the presence
of paint, grease or icing, the force on an individual post could be more than twice the line load.
For these reasons, Section 8 of these Guidelines (see Figure 8.1) recommends that the line is
taken one full turn around the leading post before the figure-of-eight belay is taken, a procedure
that reduces the loading on the most heavily loaded post. Indeed, HMPE fibre ropes have a very
low coefficient of friction on steel and two turns may be necessary to prevent overloading.
However, the recommendation in 4.4.1 above recognises that it would be unsafe to rely on the
single or double turn always being taken around the leading post.

If bitts designed to Section 4.4.1 are used with a rope eye dropped over one of the posts, without
taking any turn around the other, then that rope could safely have twice the MBL assumed in the
calculations here. (See Table 8.1).

It should be noted that, for bitts (double bollards), given the relative weakness of the baseplate
compared with the bitts, for a figure-of-eight belay the supporting hull structure should be
designed to an applied load of 2 x MBL. The hull will then also be strong enough to cope with the
loads from the rope eye described in the previous paragraph.

Section 4

4.4.2

Single Cruciform Bollard

Fitting Diagram

Geometric

Factor

Load Position

Marked

SWL of

Fitting

Design

Basis Load

Stress

Limit

(see

4.4.11)

Test

Load

Cruciform
Bollard

GF= 1.00

Cross bar
height + 0.5
rope dia.

MBL DBL=

MBL x GF

85% of

SMYS

DBL

With a single bollard, the load multiplication effect noted on the double bollards in Section 4.4.1
is absent, provided the line is secured on the cruciform bollard itself.

4.4.3 Recessed Bitt

Fitting Diagram

Geometric

Factor

Load Position

Marked

SWL of

Fitting

Design

Basis Load

Stress

Limit

(see

4.4.11)

Test

Load

Recessed
Bitt

GF= 1.00

Top of Bitt

MBL

DBL=

MBL x GF

85% of

SMYS

DBL

4.4.4 Closed Chocks

Fitting Diagram

[to re-draw ref 30º vertical]

Geometric

Factor

Load Position

Marked

SWL of

Fitting

Design

Basis Load

Stress

Limit

(see

4.4.11)

Test

Load

Closed
Chock

GF= see
Eqn.4.1
(max =
2.00)

See Note

MBL

DBL=

MBL x GF

85% of

SMYS

DBL

Load position: Outboard, horizontal

± 90

, vertical up 30

, down 90

Inboard, horizontal

±90

, vertical

±30

Because the loading arrangement shown in the diagram includes the possibility that a line may
be deflected through 180

, it is again necessary to understand that this produces a load on the

chock twice as large as the line load. The possibility of more than one line being passed through
a given chock should also be borne in mind when the method recommended in the introduction
to section 4.4 should be employed.

Section 4

4.4.5 Pedestal Fairleads and Rollers of Button-Roller Chocks

Fitting Diagram

Geometric

Factor

Load Position

Marked

SWL of

Fitting

Design

Basis Load

Stress

Limit

(see

4.4.11)

Test

Load

Pedestal
Fairlead

GF= 2.00

See Note

MBL

DBL=

MBL x GF

85% of

SMYS

DBL

GF may be reduced if measures are put in place to physically limit the wrap angle.

Load position: 180°wrap: at upper end of cylinder or conical part of throat

(at centre of roller if radiused throat).

For rollers with a typical D/d ratio of 8, Figure 6.3 indicates a strength reduction of some 15% on
the MBL for wire ropes. The DBL may be reduced accordingly.

For a single line, the geometric factor may safely be taken as 2.00, or the value given by
equation 4.1 may be used.

4.4.6 Universal Fairlead (4 Roller type)

Fitting Diagram

Geometric

Factor

Load Position

Marked

SWL of

Fitting

Design

Basis Load

Stress

Limit

(see

4.4.11)

Test

Load

Universal
Fairlead

GF = see
Eqn 4.1
and
Notes
below

See Note

MBL

DBL=

MBL x GF

85% of

SMYS

DBL

Load position: Outboard: Horizontal: ±90º, Vertical up: 30°down: 90°

Inboard:

Horizontal: ±30º, Vertical up: 15° down: 30°

For rollers with a typical D/d ratio of 8, Figure 6.3 indicates a strength reduction of some 15% on
the MBL for wire ropes. The DBL may be reduced accordingly.

For a single line, the geometric factor may safely be taken as 2.00, or the value given by
equation 4.1 may be used.

Section 4

4.4.7 Universal Fairlead (5 Roller type)

Fitting Diagram

Geometric

Factor

Load Position

Marked

SWL of

Fitting

Design

Basis Load

Stress

Limit

(see

4.4.11)

Test

Load

Universal
Fairlead

GF = see
Eqn 4.1
and
Notes
below

See Note

MBL

DBL=

MBL x GF

85% of

SMYS

DBL

Load position: Outboard: Horizontal: ±90°, Vertical up: 30°, down: 90°

Inboard:

Horizontal: 30°/ 90°, Vertical up: 15°, down: 30°

For rollers with a typical D/d ratio of 8, Figure 6.3 indicates a strength reduction of some 15% on
the MBL for wire ropes. The DBL may be reduced accordingly.

For a single line, the geometric factor may safely be taken as 2.00, or the value given by
equation 4.1 may be used.

4.4.8 Emergency Towing Arrangement

See also Sections 3.3 and 3.4, and Appendix E.

Fitting Diagram

Geometric

Factor

Load Values

and Position

Marked

SWL of

Fitting

Design

Basis Load

Stress

Limit

(see

4.4.11)

Test

Load

Closed
chock

GF= see
Eqn 4.1
and note
2

See notes

Load

(see

note 1)

DBL =
Load x GF

50%

of UTS

DBL

Section 4

Fitting

Geometric

Factor

Load Values

and Position

Marked

SWL of

Fitting

Design

Basis Load

Stress

Limit

(see

4.4.11)

Prototype
Test Load

(see Note 1)

Strong point

GF=1.00

See notes 2
& 3

Load

(see note

DBL =
Load x GF

50% of

UTS

DBL

Chafing chain for
emergency towing (see
note 4)

(if provided as chafing
gear)

Grade U3 stud link chain

(ships over 20,000 DWT)

N/A

See notes 2
& 3

As per

Load (not

marked)

DBL =
Load x 2

UTS

Up to 50,000
DWT: 2000 kN

Over 50,000
DWT: 4000 kN

Towing pennant (see
note 5)

6 x 41 WS + IWRC
galvanized wire rope
(ships over 20,000 DWT)

N/A

See notes 2
& 3

As per

Load (not

marked)

DBL =
Load x 2

UTS Test

destruction

Pick-up gear (see note 6)
(ships over 20,000 DWT)

N/A 225kN 225kN

(not

marked)

DBL =
225kN x 2

UTS Test

destruction

Notes:

1. Prototype testing is required for the complete assembly, not individual components.

2. Load values: up to 50,000 DWT:

101 t (equivalent to 1,000 kN) bow and stern

50,000 DWT and above: 203 t (equivalent to 2,000 kN) bow and stern

3. Load position:
Outboard:

Horizontal:

±90°

Vertical up: 0°, down: 30°

Inboard:

0º horizontal and vertical

4. Chafing chain:

up to 50,000 DWT:

54 mm dia; B.L.=2265 kN

50,000 DWT and above: 76 mm dia; B.L.=4295 kN

Length outboard:

3.0 m

Required forward; aft requirement depends on design.

Refer to Appendix F for analysis of strength of chain over a curved surface.

5. Towing pennant:

Up to 50,000 DWT:

58 mm diameter

Over 50,000 DWT:

76 mm diameter

Length= 2 x freeboard at chock + 50 m.
Pennant required aft: optional forward.

6. Pick-up gear:

MBL = 225kN
Size 7 polypropylene line 56 mm dia.
Length = 120 m.
Required aft; optional forward.

4.4.9 Single Point Mooring Equipment

See Section 3.3 and Appendix E, noting that test load should equal SWL.

Section 4

4.4.10 Mooring Winches

Fitting

Geometric

Factor

Load Values and

Position

Marked

SWL of

Fitting

Design Basis

Load

Stress

Limit

(see

4.4.11)

Test

Load

Mooring
Winch
Frames,
Foundations

GF=N/A

Split Drums: on first
layer.

Single Drums:
normal working layer
(second or third)

MBL

DBL=MBL

85% of
SMYS

DBL

Mooring
Winch Drum,
Shafts,
Bearings

GF=N/A

Split Drums: on first
layer.

Single Drums:
normal working layer
(second or third)

MBL DBL=MBL

See
note 1

DBL

Mooring
Winch Drive
Components

GF=N/A N/A MBL

DBL=Stall
Load

(see note 3)

See
note 2

See ISO
3730
and
Section
7

Mooring
Winch
Brakes

GF=N/A

Split Drums: on first
layer.

Single Drums:
normal working layer
(second or third)

MBL

DBL=80% of
MBL

85% of
SMYS

DBL

Notes:
1. Mooring winch drum, shafts and bearings should be designed so that the maximum stress at

DBL is

≤ 90% of yield, or so that the maximum stress at rated pull is ≤ 40% of yield, whichever

is the most severe requirement (definition of ‘rated pull’ can be found in section 7.5.1) as per
ISO 3730 parts 4.2.2 and 4.2.1 respectively.

2. Mooring drive components should be designed so that the maximum stress at Stall load is

≤

90% of yield, or so that the maximum stress at rated pull is

≤ 40% of yield, whichever is the

most severe requirement (definition of ‘rated pull’ can be found in section 7.5.1) as per ISO
3730 parts 4.2.2 and 4.2.1 respectively.

3. When using electric winches with squirrel cage multi speed electric motors, the torque

applied when shifting from one speed step to another can be higher than the stalling load and
should therefore be used as the DBL.

4.4.11 Comparison of Combined Stresses with the 85% of Yield Criterion

The equivalent stress,

, at any particular point on a fitting is given by:

)

(

−

It should be

≤ 0.85 σ

, where the specified minimum yield stress is denoted by

Section 4

4.5 STRENGTH TESTING OF MOORING FITTINGS

A load test should be performed on one fitting of each type. A manufacturer's test certificate is
acceptable if the test was witnessed by an independent authority (such as a Classification
Society) and the witness certificate lists all details such as test load, load application, dimensions
of scantlings and materials.

The test load should be applied with a rope of adequate strength to allow a line tension equal to
the 'test load' listed in Section 4.4. Alternative arrangements are acceptable if the test load is
equivalent to the resultant load from a line application.

The load test may be performed aboard the ship after all installation and structural
reinforcements are completed. It is recognised that this is unlikely to be a practical option, since
it would be very costly and time-consuming to replace unsatisfactory mooring fittings at a time
close to the delivery of a new ship.

4.6 MARKING OF MOORING FITTINGS

Mooring fittings should be marked in order to provide ship operators with information on the
strength of fittings.

Each fitting should be clearly marked by weld bead outline with its SWL as listed in Section 4.4,
in addition to any markings required by other applicable standards. The SWL should be
expressed in metric tonnes (letter 't') and be located so that it is not obscured during operation of
the fitting

For safety, the marked SWL should correspond to the load in the associated line or chain. Thus
the marked SWL will normally be the mooring line's MBL. It will not be the resultant load on the
fitting which may be higher, e.g. on a set of bitts. It should also be noted that the unit 't' is
recommended rather than the technically correct 'kN', since some operators may not be fully
familiar with the metric system and a fitting may be dangerously overloaded if 'kN' is confused
with 't'.

Since the SWL does not provide information on safety factor, test load or geometry of line
(or lines) application, and marking of all data would be impractical, the ship should be
provided with all additional relevant information. This should include actual test load
applied, geometry of load application, bitt strength when belayed by eye and higher up on
the barrel, maximum size and MBL of applicable line or chain, test certificates, standard
drawings, etc. Where twin lines may be deployed on a fitting, the SWL of single line
should be marked and the acceptability of more than one line on the fitting should be
indicated on the mooring layout plan.

Such information should be incorporated in a mooring layout plan available, or preferably
displayed, on the ship.

4.7 GENERAL RECOMMENDATIONS

4.7.1 Recommendations for Ship Designers

• Minimum safety factors listed in Section 4.4 are based upon the appropriate design

criteria and loading assumptions, and should be incorporated in all new equipment and
mooring fittings.

• All equipment and fittings should be clearly marked with their SWL (as defined in these

Guidelines) as noted in Section 4.6.

• The designer should prepare a mooring layout plan as described in Section 4.6 in

cooperation with the ship operators.

Section 5

Structural Reinforcements

5.1 BASIC CONSIDERATIONS

Mooring fittings and equipment should be connected to the ship structure in such a way that no
failure will occur under anticipated static and dynamic loadings. Section 4 gives the
recommended minimum strength criteria for the fittings or equipment and the Design Basis
Loads given in Section 4.4 should also be used for the supporting structure. However, in
principle, the strength of the supporting structure and its connection to the fitting should always
be greater than the marked SWL of the fitting. In order to achieve this, it is recommended that
the stress limit for supporting structure is taken as 80% of SMYS.

For heavy equipment such as winches, the weight of the equipment itself including dynamic
loads in a seaway should also be taken into account. It is not usually necessary to add the static
and dynamic loads caused by the ship's seaway motion to the loads generated by mooring lines
or chains, since the ship will rarely be subjected to excessive motion while moored.
Nevertheless, once the static requirements are met, the foundations of heavy equipment should
be checked for dynamic forces in the same manner as other main and auxiliary machinery.

In selecting fittings from various standards or vendors, the method of hull attachment should be
carefully considered. Simplified, less expensive fittings may require elaborate hull
reinforcements. For example, some roller fairleads do not incorporate load bearing members
between the end posts, which results in very high localised reaction loads on the deck.

Fittings or equipment generally apply tension, compression and shear stresses to the deck
structure. These stresses should be added to the hull girder stresses that may exist while the
ship is moored. The longitudinal deck stress may be assumed to correspond to the stress
generated by the maximum allowable still water bending moment. For fittings in the bow and
stern area, this stress may be ignored.

Another consideration for equipment and fittings in the mid-body area is the stress-raising effect
that any local reinforcements may have on longitudinal strength members. This applies
especially to deck plating and deck longitudinals of high tensile steel (HTS) where the ends of
reinforcing members may generate fatigue cracking in the primary structure. For this reason,
transverse reinforcing members are strongly preferred over longitudinal reinforcements. Where
longitudinal reinforcements cannot be avoided, the ends of the reinforcing members should be
very gradually tapered.

Tensile loadings (pull on deck plate) are the most difficult to accommodate. If the deck plating is
thin in relation to the member on top and the reinforcement below, the heavy welding required
could cause tearing of the deck plate. Furthermore, any misalignment between members above
and below the deck would result in high deck bending stresses. For this reason, deck insert
plates are recommended where the deck plate is thinner than the member welded to it.

Special attention should be paid to connections of fittings made from steel of higher strength
than the hull steel. If local stresses are high, and adequate compensation cannot be made using
the original hull steel quality, then local installation of higher strength steel may be necessary.

As far as practicable, mooring fittings and equipment should be located on longitudinals, beams
or girders in order to facilitate efficient distribution of the mooring load. Additional reinforcing
members may also be required to spread the load. The arrangement of foundations and
supporting structure beneath such fittings should be designed to accommodate the design loads
discussed in Section 4, considering any possible variation in the direction of the forces acting
through the connection to the fitting. Supporting structure includes that part of the ship's

Section 5

structure which is directly subjected to the forces exerted on the fitting.

Whilst this section gives practical guidance on the design of structural reinforcements, the
requirements of the Common Structural Rules for Double Hull Oil Tankers, CSR for Bulk
Carriers, the Classification Society Rules for other ship types and IACS Unified Requirement A2,
including required corrosion margins, should also be followed in applicable cases.

5.2 MOORING WINCHES

Mooring winches are normally bolted to foundations that are welded to the ship's deck. A built-
up foundation should be designed so that all parts are accessible and hold-down bolts can be
fitted from below. Vertical members are required to be suitably supported by tripping brackets
which should be positioned close to bolt holes and generally span the under-deck longitudinals
or beams.

Adequate drain holes should be provided to avoid any entrapment of water, which could lead to
corrosion damage.

As an alternative to a built up foundation, the mooring winches can be installed directly on to the
deck. This foundation is easy to maintain as there is no obstructing structure above the deck and,
owing to the lower height, there is no need to provide raised operating platforms. The deck plate
below the winch is reinforced by increased thickness and adequate carlings below deck.

Steel chocks or pourable resin compound may be fitted between the foundation and the
machinery bed plate. Resin chocks should be of suitable and proven material, with the
composition properties, along with mixing and pouring procedures covering installation, being in
accordance with Classification Society requirements.

If steel chocks are used, an area on the foundation top plate may require machining.

If resin chocks are fitted, the top plate should be sized taking into account the necessity of fitting
dams to retain the resin.

The surfaces where resin chocks are to be used should be cleaned and the hold-down bolt
torque should not exceed the resin chock supplier's recommendation.

Brake anchors should be designed to meet the design criteria given in Section 4. For loads in
excess of about 100 tonnes (981 kN), the brake anchors should preferably be carried through
the deck. Alternatively, brake anchors can be welded to the foundation with adequate toe
brackets in line with deck stiffeners. Welding should be full penetration type. Local deck insert
plates may also be necessary.

An abutment or end stopper may be welded to the foundation at points predetermined by the
machinery manufacturer to reduce the hold-down bolt's shear loading and to reduce the need for
fitted bolts.

Foundations of all winches of greater than five tonnes rated pull may require to have abutments
fitted.

An under deck support structure should be provided in line with the foundation above the deck.
For winches in the mid-body area, the support should preferably be in a transverse direction and
be of adequate size and span to distribute the load into existing deck longitudinals.
Reinforcement of existing longitudinals should be avoided if at all possible to prevent fatigue
cracking at the ends of reinforcements.

Where tension loads are applied to the deck, it may be necessary for welding above and below
the deck to be of the full penetration type. Other type weld sizes should be checked for
adequacy. Where foundation members line up with existing deck structure, the standard weld
size of deck longitudinals, beams or transverse webs may also have to be increased.

Section 5

Examples of good pin-to-pedestal connection and pedestal-to-deck connection are shown in
Figures 5.5 and 5.6.

The reinforcement below the deck should be extended to adjacent strength members so as not
to concentrate the stress on longitudinal girders and/or any other hull members over their
allowable stress level as shown in Fig 5.7.

5.5 BITTS

Bitts require deck strengthening members in line with all four sides of their base. The members
below deck should be of the same thickness as the base, and their welding to the deck should
be equal to the weld size between bitt base and deck. Where bitts line up with existing structure,
such as deck beams, girders, or transverse webs, the welding of these members to the deck
may have to be increased.

5.6 RECESSED BITTS

For high freeboard ships such as LNG carriers, bitts recessed in the ship's side may be required.
As far as practical, recessed fittings should be located in way of existing structure, such as
longitudinals, stringers, and web frames. Additional reinforcing members of adequate size and
span to distribute the load into the existing structure may also be required.

Special attention should be given to the design of local reinforcements in fatigue sensitive areas
of the side shell in order to minimise stress concentrations. For this reason, transverse
reinforcing members are preferred where practical and reinforcement of existing longitudinals
should be avoided if possible to prevent fatigue cracking at the ends of reinforcements. If
longitudinal reinforcements cannot be avoided, the ends of the reinforcing members should be
gradually tapered. Where recessed fittings line up with existing structure, the standard weld size
of these members may also have to be increased.

5.7 SPM FITTINGS AND SMIT BRACKETS

Due to the high loading on these fittings, the method of connection to the hull structure should be
given due consideration. Each chain stopper or Smit bracket should be welded directly to the
deck of the ship or welded or bolted to a plate or pedestal structure which is in turn welded to the
deck. The stopper or bracket should not be bolted directly to the deck of the ship. A heavy deck
insert plate may be required. In place of one centreline girder, two parallel girders with spacing
equal to the distance between the cheek plates of the chain stopper or SPM bracket are
recommended. Additional transverse members and pillars may be required to absorb the load.
The SPM or towing fitting should be located as close to the deck as possible. However, a small
foundation will normally be required to achieve proper alignment between the fitting, the bow
chock and the pedestal fairlead. The foundation must be provided with a thrust block capable of
absorbing the chain load specified in Section 4. Further guidance on SPM fittings is given in
Reference 1 "Recommendations for Equipment Employed in the Bow Mooring of Conventional
Tankers at Single Point Moorings."

5.8 TUG PUSH POINTS

With the advent of ever more powerful tugs, side shell reinforcement for tug pushing should be
carefully considered. Calculations should consider the maximum expected tug pushing force and
the contact area in order to determine the design pressure.

At each push point the vertical extent of reinforcement should take into account the full range of

Section 5

area. The rounded plate is usually of Grade “D” or “E” steel to prevent propagation of major
cracks in the hull envelope. Most Classification Societies place restrictions on the direct welding
of mooring fittings to this plate. Since mooring chocks or fairleads in the mid-body area should be
flush with the side shell to avoid line chafing on the rounded gunwhale, either doublers or a
cantilevered foundation will be required for all shipside mooring fittings. Figure 5.2 shows such
an installation.

5.9.2 Doublers Versus Inserts

Deck plating in way of mooring fittings may be reinforced by doublers or ideally by insert plates.
Doublers are usually less expensive but cannot transmit large tensile loads and will be subject to
specific Class Society requirements covering welding. This is because all loads to the deck are
transmitted only through the fillet welds or plug welds of the doubler and these are seldom in line
with stiffening below the deck. Doublers are more suitable for small fittings, such as eyes, since a
small insert plate in a highly stressed upper deck may lead to crack initiation due to the additional
locked-in stress created by the welding. For mooring outfits on the bow and stern where the
deck's longitudinal stress is insignificant and the thickness is much less than midships, insert
plates should be used.

Where doublers (or pads) are used, the width should be small to prevent bending under tension
loads. The following table provides details of typical pad widths and thicknesses which may be
used as a guide:

Leg thickness of

Pad width (mm)

Pad thickness (mm)

fittings (mm)

(max)

Less than 12

12-13

14-16

17-19

20 and above

TABLE 5.1: TYPICAL PAD WIDTH AND THICKNESS

Note: (a) Pad corners should be provided with a minimum of 20 mm radius. The shape of pads should be

designed to suit that of legs of fittings.

(b) A greater pad width causes failures (separation of the pad from the deck plate) at

lower loads.

5.9.3 High Strength Steel Fittings

Some mooring fittings may be built of high tensile steel (HTS) to reduce weight or to improve
strength. Connections of such fittings, especially when the deck structure is of a lesser strength
steel, should be carefully calculated. Where the maximum stress occurs at the base of the fitting
(such as the frame of a universal chock) and the deck is not of HTS or of a sufficient thickness, a
deck insert plate of HTS may be required along with HTS strengthening members below the
deck. Likewise, existing structures such as deck beams directly in line with HTS members above
the deck may have to be locally replaced with HTS members. If the deck connection and
reinforcing method are carefully considered before designing or selecting fittings for a ship,
installation will be simplified and overall costs reduced.

Section 6

Section 6

Mooring Lines

6.1 GENERAL

A major decision should be made at the ship design stage regarding the type of mooring line to
be used. The type of line will influence issues such as winch drum size, type and bend radius of
chocks and fairleads and required deck space.

Low stretch ropes made from steel wire or synthetic materials such as High Modulus
Polyethylene (HMPE) or Aramid fibres are advantageous where limited movement is required,
such as at berths with hard arm equipment and where low dynamic loads are expected. These
ropes are therefore recommended on large ships. If high dynamic loads are expected, a number
of solutions are possible, such as the fitting of longer tails or higher stretch tails or the provision of
more elastic mooring lines.

Synthetic lines having greater elasticity may be more appropriate for use on small ships where
ease of handling, flexibility of moorings and lower line tension are important criteria.

Other factors which may influence the choice of material include cost and the type of outfitting
customarily used within a particular trade.

A mixed system utilising low stretch spring lines and more elastic breast lines, as found

on some

ships, has certain theoretical advantages. It reduces the fore and aft excursion of the ship while
moored, which in turn reduces shifting of loads from one breast line to another and limits the
motion of loading arms or hoses. Nonetheless, it is recommended that all lines be of the same
size and material (See Section 1).

The properties and performance of steel wire and high modulus synthetic ropes are described in
Sections 6.2 and 6.4, while those of the other, more elastic, conventional fibre ropes are covered
in Section 6.3.

6.1.1 General Safety Hazards

All mooring lines can pose a great danger to personnel if not properly used. Handling of mooring
lines has a higher potential accident risk than most other shipboard activities.

A significant danger is snap-back, the sudden release of the energy stored in the tensioned
mooring line when it breaks.

When a line is loaded, it stretches. Energy is stored in the line in proportion to the load and the
stretch. When the line breaks, this energy is suddenly released. The ends of the line snap back,
striking anything in their path with significant force.

Snap-back is common to all lines. Even long wire lines under tension can stretch enough to snap
back with considerable energy. Synthetic lines are more elastic and thus the danger of snap-
back is more severe.

Line handlers must stand well clear of the potential path of snap-back, which extends to the
sides of and far beyond the ends of the tensioned line. Figure 6.1 illustrates potential snap-back
danger zones.

A broken line will snap back beyond the point at which it is secured, possibly to a distance almost
as far as its own length. If the line passes around a fairlead, then its snap-back path may not
follow the original path of the line. When it breaks behind the fairlead, the end of the line will fly
around and beyond the fairlead.

It is not possible to predict all the potential danger zones from snapback. When in doubt,
personnel should be kept well away from any line under tension.

When it is necessary to pass near a line under tension, it should be done as quickly as possible.

Section 6

If work must be undertaken near a line under tension, it should be done quickly and the danger
zone should be vacated as soon as possible. The activity should be planned before approaching
the line and the number of personnel near the line should be kept to a minimum. If the activity
involves line handling, it should be ensured that there are enough personnel to perform it in an
expedient and safe manner.

High modulus synthetic fibre ropes have similar breaking characteristics to wire ropes. However,
snap-back from these ropes will generally be along the length of the line and not in a snaking
manner, as found with wire ropes.

6.1.2

Strength Criteria

Ship designers will normally have determined the mooring restraint requirements for large ships
under standard environmental criteria assuming all mooring lines are steel wire ropes.

Before fitting wire ropes or high modulus synthetic fibre mooring ropes, ship operators should
conduct a mooring analysis to determine and demonstrate the adequacy of the mooring
arrangement.

Recommended minimum safety factors (SF) for steel, polyamide and other synthetic mooring
ropes are given in Table 6.1 below.

FITTING

SWL

SF = MBL/SWL

% MBL

TEST LOAD

Mooring lines

Highest load calculated
for adopted standard
environmental criteria

Steel: 1.82

Polyamide

(2)

: 2.22

Other Synth: 2.00

55%

45%

50%

Test sample to destruction
to confirm MBL

(3)

Tails

(1)

for Wire

Mooring Lines

As above

Polyamide

(2)

: 2.50

Other Synth: 2.28

As above

Tails

(1)

for

Synthetic
Mooring Lines

As above

Polyamide

(2)

: 2.75

Other Synth: 2.50

As above

Joining Shackle

Equal to or greater than
mooring lines to which
attached

2.00

Proof Load

TABLE 6.1: STRENGTH CRITERIA

Notes: 1) Tails will have a higher breaking strength than mooring lines (steel and synthetic) since they

will take most of the fatigue and are subject to more abrasion.

2) For polyamide, the SF is higher due to allowance for the strength loss when wet.

3) MBL is defined as the minimum load which a new rope will sustain before breaking when

tested to destruction. Ref ISO 3108 (steel wire ropes) and ISO 2307 (fibre ropes).

6.1.3

Record Keeping

All mooring ropes, wires and tails should be received with either individual certificates, or, if part
of a batch, a certificate of conformity.

These certificates should be retained and contain typically the following information:

• Manufacturer
• Date
•

Description of rope, including:

type

reference number in mm per diameter, weight per meter

length

material

rope construction (e.g. laid, braided, number of strands)

jacketing information (material and construction)

end terminations

Section 6

•

Minimum Breaking Load (MBL)

It is recommended that on receipt, all ropes, wires and tails should be permanently marked in
order that positive identification with their appropriate certificate can be made.

Records of date placed in use, inspections and any maintenance should be kept.

6.2 WIRE MOORING LINES

6.2.1 Material

To meet the requirements of increased strength for wire mooring lines, manufacturers have
developed pre-formed, drawn galvanised wire with high tensile strengths. The drawn galvanised
wire provides strengths of the same magnitude as bright wire and an improvement in wire line
quality. To save weight, preformed drawn galvanised wire strands of a minimum tensile strength
of 1,770 N/mm

are recommended.

6.2.2 Construction

A line should be selected which combines the proper attributes for mooring when reasonable
flexibility and high MBL are priority requirements. The recommended construction is 6 x 36 or 6 x
41 (6 x 36 class) with the wires in each strand of equal lay and the strands of regular (ordinary)
right hand lay.

Figure 6.2 illustrates these constructions. Equal lay for lines in each strand is recommended
when available because of its higher MBL than cross lay. While Lang’s Lay lines have a slightly
greater MBL than regular lay lines, they have a greater tendency to kink and unlay (or open up
the lays of the strands) which is undesirable where grit, dust and moisture are present.

Steel wire lines with an independent wire rope core (IWRC) are strongly recommended over fibre
core steel wire lines for several reasons. An IWRC steel wire line has a much greater resistance
to crushing, higher MBL for a given diameter and greater strength retention when bent.

If steel wires are used for mooring large ships, it is recommended that as a minimum 38 mm
diameter 6 x 36 class IWRC wires are employed, manufactured from preformed, heavily drawn
galvanised wire, having tensile strengths ranging from 1,770 to 1,960 N/mm

6.2.3 Corrosion Protection

Corrosion protection can be provided by galvanising individual wires. Galvanising should be
carried out in accordance with EN 10264-2:2002 or equivalent. These standards specify the zinc
weight per wire surface as a function of wire diameter. The zinc weight ranges from about 100
g/m

for a 1.0 mm

diameter wire to 220 g/m

for a 2.5 mm diameter or greater wire.

Section 6

Steel Wire Rope

6 x 36 class

(1960 steel core)

Dia. (mm)

Weight

Kg/100 m

MBL

24 236

402

26 276

472

28 321

547

30 368

628

32 419

715

36 530

904

40 654

1,120

44 792

1,350

48 942

1,610

52 1,110

1,890

56 1,280

2,190

60 1,470

2,510

64 1,700

2,800

68 1,900

3,100

72 2,200

3,500

76 2,400

3,800

80 2,700

4,200

TABLE 6.2: TYPICAL MBLs OF STEEL WIRE ROPE

6.2.4 Bend Radius

Wire ropes will lose strength when bent over a radius. This is a major factor in the design of
shipboard equipment for wire rope, since items such as winch drums and fairleads should have
an adequate diameter or surface radius. The recommended minimum values listed in sections 7
and 8 are based on lines with the recommended independent wire rope core. A fibre core rope
will lose more strength at a given bend ratio than an IWRC rope. This is clearly shown in Figure
6.3.

As a general rule, a minimum bend ratio of 12 is recommended. Where this would create
problems with the size of the fitting, a ratio of 10 is an acceptable compromise for items such as
universal roller fairleads, following validation that the reduction in breaking strength/fatigue is
acceptable.

Section 6

6.3 CONVENTIONAL FIBRE MOORING LINES

6.3.1

General

The most common materials used for fibre mooring lines are polyester, polyamide,
polypropylene and polyethylene. Some ropes are made of combinations of these materials.

Table 6.3 details materials used in making synthetic ropes and the general characteristics. Table
6.4 states typical strengths for ropes of different materials. Figure 6.5 shows typical elongation
values for various rope materials.

Material

Specific

Gravity

Specific

Modulus

N/tex

Specific

Strength

N/tex

Dynamic

Coefficient

of Friction

against

Metal

Melt Point

Deg. C

Other

Characteristics

Polyester

1.38

0.84

0.12 – 0.15

256

Good wet internal
abrasion resistance.

Polyamide

1.14

0.84

0.1 – 0.12

218

10-15% Wet Strength
loss. Poor wet
internal abrasion
resistance

Polypropylene

0.91 8 0.73

0.15

–

0.22

165

Lighter than water.
Low strength.

Polypropylene/
Polyethylene
(mixed
polyolefins)

0.92 –

0.94

0.84

0.1 – 0.15

140

Lighter than water.
Reasonable strength,
better abrasion
resistance than
polypropylene.

Polyester/
Polyolefin dual
fibres

0.99 –

1.14

0.8

0.1 – 0.15

140

(polyolefin)

256

(polyester)

Good wet/dry
abrasion resistance.

Polyamide
mono and fibre
mixture

0.98 –

1.14

0.84

0.1 – 0.12

165/218

Compact. Good
abrasion resistance
for use on winches.

Polyester/
Polypropylene
melt mixture

0.99 8 0.80

0.12

–

0.15

173

Lighter than water.
Stronger than
polypropylene.

Notes:

Table indicates approximate values, actual properties may vary.
The unit, "tex", is the weight in grammes of 1,000 metres of material.
Newtons/tex = MN / (kg/m), where kg/m is rope linear density.
Multiply Newtons/tex by 102.3 x SG to obtain kg / mm

Multiply Newtons/tex by 145,400 x SG to obtain lb / in

TABLE 6.3: TYPICAL CHARACTERISTICS OF MATERIALS USED FOR CONVENTIONAL

SYNTHETIC ROPES

6.3.1.1

Polyester

Polyester is the most durable of the common materials. It has high strength, both wet and dry. It
has good resistance against external abrasion and does not lose strength rapidly due to cyclic
loading.

Polyester's low coefficient of friction allows it to slide easily around bitts. Its relatively high melting
point (256°C) reduces the chances of fusion. Polyester is therefore useful for large and small
rope material where strength and durability are important and where moderate elasticity is
required.

6.3.1.2 Polyamide (previously referred to as 'Nylon')
Polyamide rope loses 10 – 15% of its strength when wet. It has the highest elasticity of regularly
used materials with good temperature and abrasion resistance.

Section 6

TABLE 6.4: MINIMUM BREAKING FORCES IN kN OF SYNTHETIC ROPES (NEW, DRY ROPES, UNSPLICED)

Notes:

1. ‘Ref. Number’ is the approximate diameter in millimetres

2. A spliced test piece must achieve at least 90% of EN and ISO standard values

Polyester

Polyamide

Polypropylene

Polyester mixed

Polyolefins

Polyester/Polyolefin

dual fibres

Polyamide

Polyester

Polyamide

Mono and

Fibre mixture

Polyester/

Polypropylene

melt mixture

Split mono

Multi PP2

High

Strength

Multi PP 3

Higher

strength

Double

braided

Higher strength

Double braided

Double

braided

Higher strength

Double braided

EN ISO 1141 EN ISO 1140

EN ISO 1346

EN 14687

EN 14686

EN 14685

EN 14684

Ref Number

kN kN

24 86.1 112 78.8

82.6

104

96.3

107 103 124 96.8 121

115

26 101 129

91.5

104

121

113

125

121 145 113 141

136

28 116 149 105

119

139

130

144

140 168 130 163

155

30 132 170 119

136

158

148

164

161 193 149 186

178

32 150 192 134

154

179

167

186

183 219 168 210

206

36 188 240 167

191

224

210

233

231 277 211 264

259

40 230 294 204

233

274

257

285

284 341 259 324

324

320

44 276 351 243

278

327

308

342

343 412 311 389

412

382

48 326 412 286

327

385

364

404

408 490 368 460

491

449

52 380 479 332

379

448

424

471

478 574 430 537

530

521

56 437 550 381

436

514

489

543

554 665 494 618

657

599

60 500 627 433

495

583

558

620

635 762 566 707

706

680

64 566 709 488

558

657

631

701

723 867 640 800

804

769

72 708 887 608

692

820

789

877 917 1,100 800 1,000 1,059

961

80 867 1,080 740

850

995

963

1,070

1,130 1,350 984 1,230

1,236

1,184

88 1,040 1,300 887

1,010

1,190

1,160 1,290 1,360 1,630 1,180 1,480

1,344

96 1,230 1,530 1,040

1,190

1,400

1,370 1,520 1,620 1,940 1,400 1,750

1,589

Section 6

6.3.1.3 Polypropylene

Polypropylene rope has approximately the same elasticity as polyester rope. Polypropylene has
limited temperature resistance and has poor cyclic loading characteristics. Prolonged exposure
to the sun's ultraviolet rays can cause polypropylene fibres to disintegrate due to actinic
degradation.

Polypropylene is lighter than water and can be used for floating messenger lines. The use of
moorings manufactured from 100% polypropylene is not recommended. However, suitable
composites or melt mixes with other fibres such as polyethylene or polyester are available and
acceptable for use as moorings.

6.3.1.4 Combinations of Materials

The following describes the characteristics of some examples of ropes manufactured by
combining different materials:

Polyamide mono and multifilament fibre mixtures

These ropes are very compact, have good abrasion resistance and are designed for use as
winch-mounted lines.

Polyester/Polyolefin

dual fibres

These ropes are produced with yarns which are made with polyester fibres covering a polyolefin
core. Minimum breaking force, abrasion resistance and cyclic rope performance are equivalent to
polyester ropes of the same size and construction.

Polypropylene/Polyester melt mix

These ropes are made using fibres made of a melt mixture of polyester and polypropylene during
extrusion. This rope is significantly stronger than polypropylene rope and will float on salt water.

Mixed Polyolefin ropes

These ropes are made using bi-component fibres made of a blend during extrusion of
polypropylene and polyethylene. Mixed polyolefin ropes offer a higher degree of resistance to
abrasion and strength compared to regular polypropylene.

6.3.2 Construction

Figure 6.4 shows the common structures used in synthetic ropes.

The four and six-strand with core structures are twisted ropes similar to conventional wire rope
and are sometimes used for mooring lines. They may be prone to hockling.

The eight-strand (sometimes called square braid or plaited) and twelve-strand braided ropes, are
constructed of left and right-hand laid strands to give a torque-free rope. They are easily
spliceable and provide a good rope structure for mooring lines.

Double braid ropes, sometimes called braid-on-braid, are constructed of a core braided of many
small strands and surrounded by a cover which is also braided of many small strands. The cover
provides an integral component to the line’s strength and neither the core nor the cover should
provide more than 55% of the overall weight. They are commonly used for mooring hawsers at
single point moorings (SPMs) and for tails on wire ropes.

Parallel strand ropes have the core ropes protected by a non-load bearing protective jacket.
They are commonly used for regular mooring ropes and as SPM mooring hawsers.

6.3.3 Bend Radius

The strength and life expectancy of fibre rope is directly related to the bend radius that it is
exposed to in-service.

The rope manufacturer’s guidelines on acceptable minimum bend radius should be consulted for
each specific application.

Section 6

6.3.4 Handling and Storage of Synthetic Lines

Handling

Crews handling synthetic lines which must be stoppered off and made fast to bitts need good
training in safe mooring practices. Surging of lines on winch warping drums is not recommended
for synthetic lines. The nature of the fibres, combined with the high loads, make it necessary
when providing slack to walk back the winches rather than surge the lines.

Stoppers made of polyester are recommended. They should be used in double line
configurations, where a half hitch is placed over the bitts and the two ends of the stopper are
crossed over and under the line being stoppered off. Training should include action to be taken
during a break-out incident, namely, clearing the area to prevent injuries.

When holding and tensioning the line on the warping drum, capstan or bitt, the line handler must
not stand too close. When the line surges, he could be drawn into the drum or bitt before he can
safely take another hold or let go. He should stand back and grasp the line about 1 m from the
drum or bitt.

Synthetic lines are not very resistant to cuts and abrasion and should not be exposed to
conditions which might damage them. If they are used in chocks or fairleads previously used
with wires, it should be ensured that the surfaces have not become grooved or roughened by
the wires. It may be necessary to grind the chocks or fairleads smooth.

Care should be taken when dragging synthetic lines along a deck and contact with sharp edges
and rough surfaces should be avoided. When possible, small lines should be carried instead of
dragged.

When dirt, grit or rust particles are allowed to cling to and penetrate into synthetic ropes, internal
abrasion will result. The rope should be brushed or cleaned before storing.

Twisted ropes can be harmed by kinking, which may form into hockles if not properly removed.
When a kink forms, the load must be removed and the kink gently worked out.

Twisted rope must be coiled in the proper direction. Most lines are right-hand lay and should be
coiled clockwise. When removing new rope from a coil, the coil should be suspended on a shaft
and rotated.

Winch-mounted synthetic lines should be periodically end-to-ended to distribute wear.

Storage

Synthetic lines should be stored in clean and dry surroundings. Excessive heat can damage
synthetic fibres, especially polypropylene and polyethylene. Synthetic ropes should not be
stored near steam pipes or against bulkheads which may reach high temperatures.

Ultraviolet rays from sunshine can damage fibres. Polypropylene and polyethylene are
particularly vulnerable. The potential degree of damage increases as the rope size decreases
and small polypropylene or polyethylene ropes should never be stored in direct sunlight.

Synthetic fibres are also subject to chemical damage. Their susceptibility depends on the
chemical and the fibre. Polyamide is damaged by acids and bleaching agents. Polyester is
damaged by some alkalis. Industrial solvents, including paint thinners, will damage most
synthetic lines if they are stored in paint lockers or near paints and paint fumes.

Oil and petroleum products will not normally damage synthetic fibres. Nonetheless, care should
be taken to avoid contact with them. If a rope becomes oily, it is more difficult to handle. Dirt and
grit will adhere to the oil and cause internal abrasion of the rope. If the line becomes oily or
greasy, it should be scrubbed with fresh water and a paste-like mixture of granulated soap. For
heavy accumulations of oil and grease the line should be scrubbed with a solvent such as
mineral spirits and finally rinsed with a solution of soap and fresh water.

Further guidance on Handling, Inspection and Removal from Service is provided in Appendix D.

Section 6

6.4 HIGH MODULUS FIBRE MOORING LINES

6.4.1

General

The term "High Modulus Fibre Mooring Lines" generally refers to ropes made from high modulus
fibres such as Aramid and High Modulus Polyethylene (HMPE). These fibres are much stronger
than conventional synthetic fibres such as polyamide, polyester and polypropylene.

Although some materials are sensitive to UV degradation, this is only a surface effect and does
not pose a problem for lines in excess of 24 mm diameter.

6.4.2

Properties of High Modulus Synthetic Fibres

The properties of high modulus synthetic fibres and steel wire ropes are summarised in Tables
6.5 below.

Material

Specific
Gravity

Specific

Modulus

N/tex

Specific

Strength

N/tex

Dynamic

Coefficient

of Friction

Against

Metal

Melt Point

Deg. C

Other Characteristics

Aramid

1.44

2.03

0.15

Chars @

500

Potential axial compression
fatigue problems, but these
can be overcome.

Long tension/tension
fatigue life

LCP

(Liquid
Crystal
Polymer)

1.40

2.4

0.13

300

High strength and low
stretch.

Long term durability to
fatigue.

HMPE

High
Modulus
Polyethylene

0.97

110

3.5

0.07

147

Low melt point. Lighter
than water.

Long tension/tension
fatigue life.

Steel wire

7.85 26 0.18 0.23* 1,600

Corrodes. Heavy.

Moderate tension/tension
fatigue life.

Notes:
Table indicates approximate values, actual properties may vary.
The unit, "tex", is the weight in grammes of 1,000 metres of material.
Newtons/tex = MN / (kg/m) where kg/m is rope linear density.
Multiply Newtons/tex by 102.3 x SG to obtain kg / mm

Multiply Newtons/tex by 145,400 x SG to obtain lb / in

* Steel wire is 0.23 but when lubricant/finishing is used, the coefficient may vary.

TABLE 6.5: TYPICAL PROPERTIES OF HIGH MODULUS SYNTHETIC FIBRES AND STEEL

WIRE ROPES

6.4.3

High Modulus Synthetic Fibre Materials

6.4.3.1

Trade Names

High modulus synthetic fibres can generally be identified by trade names. The following table is
provided to assist in identifying some of the common fibre trade names in use. It is not intended
as an endorsement of any particular product nor is it intended to be a complete list of fibre trade
names.

Section 6

The table describes the trade names used by fibre manufacturers. Rope manufacturers process
these fibres into rope types with their own specific trade names.

Fibre Type

Common Trade Names

ARAMID

"TWARON"

"KEVLAR"

"TECHNORA"

"HERACRON"

"APTEK"

LCP "VECTRAN"

HMPE

"DYNEEMA"

"SPECTRA"

TABLE 6. 6: EXAMPLES OF HIGH MODULUS SYNTHETIC FIBRE TRADE NAMES

6.4.3.2

Aramid Fibres

Aramid fibre typically has high strength and low stretch. It does not creep and does not melt but
chars at high temperatures.

Normally Aramid fibre mooring lines are produced in 3, 4, or 6 strand laid constructions. Aramid
ropes do not float. They are typically covered (jacketed) with some other synthetic fibre such as
polyester to increase abrasion resistance and to protect against UV degradtion.

Aramid is susceptible to axial compression fatigue that occurs when tightly constrained fibres are
forced into axial compression. Such problems may be avoided with proper attention to rope and
termination design. It is important to ensure that the correct diameter to diameter ratio is
implemented.

Aramid has very good fatigue properties (tension-tension fatigue life).

6.4.3.3 Liquid Crystal Polymer (LCP) Fibres

Liquid crystal polymer fibres have high strength and low stretch and excellent resistance to creep
and flex fatigue. The fibre has a temperature resistance between HMPE and Aramid.

LCP fibres have excellent long-term durability to fatigue, cutting and abrasion.

6.4.3.4

High Modulus Polyethylene (HMPE) Fibres

High Modulus Polyethylene (HMPE) is a fibre with high strength per weight ratio and low stretch
characteristics. HMPE fibres have very good fatigue and abrasion properties but limited
temperature resistance, having a maximum working of 70ºC.

Ropes constructed from 100% HMPE fibres float. However, jacketed HMPE ropes can have a
higher density and may sink.

HMPE has good resistance to axial compression, has a low coefficient of friction and good
abrasion resistance.

6.4.4 High Modulus Synthetic Rope Constructions

High modulus synthetic fibres can be constructed into usable ropes in a variety of forms. Most
high modulus synthetic fibre ropes used as shipboard mooring lines are variations of the basic
constructions used for conventional fibre ropes as depicted in Figure 6.4.

Section 6

6.4.5 Characteristics

6.4.5.1 Strength

High modulus fibre ropes demonstrate an increase in strength above their MBL during the early
part of their service life. This over-strength could typically be apparent for many months on a
mooring line designed for a service life of 10 – 15 years. The implications of this characteristic are
discussed in Appendix B.

Table 6.7 depicts the average minimum breaking loads of a variety of rope products from various
manufacturers and is provided for guidance only. Strengths of similar fibres published by the
respective manufacturers were referenced in developing this table. When purchasing ropes for
specific applications, manufacturer’s data should be referenced (see 6.1.2).

At this time there are no national or international standards which specify the minimum strengths
for high modulus synthetic lines.

High modulus fibre ropes have strength and diameters broadly equivalent to those of wire ropes.

HMPE 12 Strand

Aramid 7 Strand Wire Lay

Ref

Number

Weight

Kg/100m

MBL

Weight

Kg/100m

MBL

24 32.9

506

455

26 38.0

578

533

28 44.2

657

615

30 50.5

741

692

32 56.8

838

748

36 71.0 1,002

871

40 86.8 1,220 103 1,080
44

105 1,430 127 1,410

124 1,650 149 1,610

145 1,890 175 1,850

168 2,170 205 2,080

193 2,420 235 2,380

220 2,720 268 2,670

248 3,010 300 3,010

278 3,410 335 3,350

309 3,770 373 3,700

342 4,120 415 4,100

TABLE 6.7: TYPICAL MBLs OF HIGH MODULUS SYNTHETIC FIBRE ROPES

Note: ‘Ref. Number’ is the approximate diameter in millimetres

6.4.5.2 Elasticity

Figure 6.5 shows the typical broken-in load extension characteristics for steel wire, conventional
synthetic fibre and high modulus synthetic fibre ropes. The broken-in characteristics are
determined by cycling the ropes ten times to 50% of their rated strength following procedures
recommended in the OCIMF "Guidelines for the Purchasing and Testing of SPM Hawsers"
(Reference 7). This accelerated test procedure approximates the change in elasticity that might
occur over many more cycles under lower tensions in typical service.

Conventional synthetic ropes such as polyamide, polyester and polypropylene are considerably
more elastic than high modulus synthetic fibre ropes. High modulus synthetic fibre ropes are
marginally more elastic than steel wire ropes, however the ratio of extension is significantly closer
to that of steel wire than conventional synthetic ropes. The elastic properties of high modulus
synthetic fibre ropes and steel wire ropes do not change significantly with use. The elasticity
characteristics of any particular high modulus synthetic fibre rope may differ slightly from the
typical characteristics shown in Figure 6.5 and may be affected by the degree of twist applied to
the yarns and strands in the rope.

Section 6

Accepted mooring practice requires all lines in the same service, i.e. breast lines, spring lines
etc., to be of the same size and type. While the load extension characteristics of high modulus
synthetic fibre ropes approach that of steel wire ropes, the use of different materials in the same
service should be avoided.

Steel wire ropes should not be led through the same chocks as soft ropes as it may cause
chafing damage. (See also Section 6.4.7.2 ).

FIGURE 6.5: LOAD-EXTENSION CHARACTERISTICS

Wire and Fibre Ropes, New and Broken-In

(Reference 10 and 11)

Note- add 'or mixed polyolefins' to the legends 'polyester or polypropylene' – both new and broken-in

The synthetic fibre rope test data used in developing the load-extension characteristics were
determined from tests conducted using OCIMF's hawser test procedures (Reference 7). For
example, the broken-in characteristics are measured on the tenth cycle to 50% strength. Most
ropes will approach these characteristics within a few cycles and will not change significantly
even after many more cycles. These load extension curves apply to a loading rate of over a
minute or more, rather than typical wave loading periods of 10 seconds. This will apply to most
sheltered mooring situations.

If the same ropes had been tested by some other procedure, the resulting load-extension
characteristics might appear to be considerably different. Some of the variables which affect rope
load-extension characteristics are the number of cycles, cyclic load range, relaxation time, rate of
loading, and whether the rope is wet or dry.

For exposed moorings, when vessel wave induced motions may be present, constant cyclic
loading will occur and a significantly stiffer curve will result, especially at higher mean loads.

6.4.5.3 Chemical Resistance

It should be noted that, although high modulus fibres generally exhibit resistance to many
chemicals, good housekeeping and prudent care are essential in the protection of the fibres.
Whenever ropes become contaminated with a chemical, thorough rinsing with fresh water will
help to extend the useful service life.

Aramid, LCP & HMPE

Polyamide, Double Braid
Broken-in

Polyamide, 3- & 8-Strand
Broken-in

Polyamide, all
New

Section 6

Reference should be made to manufacturer’s data or the relevant national or international
standards for detailed information on chemical resistance.

6.4.6 Selection Criteria

Typical high modulus synthetic fibre ropes are as strong as steel wire ropes, size-for-size and are
lighter, more flexible and easier to handle. However, they are more susceptible to abrasion
damage and have a lower working temperature.

Selection between high modulus synthetic fibre ropes and steel wire-mooring ropes involves
evaluating a combination of factors, such as strength, construction, elastic elongation
characteristics and life expectancy, as described below.

6.4.6.1

Strength

The strength of a given size of rope will have an impact on its life expectancy. Also, ropes
subjected to loads that are a higher percentage of the breaking strength have to work harder and
as a result will have to be retired sooner.

6.4.6.2 Construction

Rope construction is an important factor that should be considered when assessing the suitability
of a rope for a particular service. Construction may also impact on the ease of in-service splicing
and will effect load extension. The ability of a rope to resist external and internal abrasion
damage may be improved by the addition of an abrasion resistant jacket.

6.4.6.3 Elastic Elongation

High modulus ropes have low elastic elongation properties which provide good control of
station-keeping. However, this results in them being more susceptible to damage from shock
loading. To mitigate this problem "shock absorbing" mooring tails may be used.

6.4.6.4 Coefficient of Friction

Unjacketed high modulus mooring lines have significantly lower coefficients of friction than
conventional synthetic or steel wire ropes. A minimum of 10 turns will be necessary on tension
drums to compensate for the loss of grip. Jacketed high modulus ropes typically are covered with
conventional materials, such as polyester or polyamide and have the same coefficient of friction
as lines made of these fibres.

The low coefficient of friction combined with the low melting point of HMPE, can lead to melting
damage when the lines are allowed to slip under load. The use of jacketed HMPE fibre ropes or
the use of anti-chafe gear can help to insulate the fibres from the heat generated.

Due to their low coefficient of friction and the danger of sudden surging, HMPE ropes should not
be manually handled on warping drums. The low coefficient of friction will also necessitate the
provision of a secure method of anchoring the rope end to the winch drum.

6.4.7 Installation

6.4.7.1 General

During the design and selection of mooring equipment which is intended to be outfitted with high
modulus synthetic fibre mooring ropes, it is recommended that the rope supplier/manufacturer is
consulted. Fairlead design and surface quality in particular can have a significant impact on the
life expectancy of high modulus synthetic fibre mooring ropes

6.4.7.2 Chafe Protection

To avoid chafing damage to high modulus synthetic fibre mooring ropes, all contact surfaces
should be regularly inspected, be kept smooth and free from chafe points. Ideally, steel fairleads
should be highly polished to at least RA10 standard but in practice this may be difficult to achieve
or maintain, unless stainless steel is used. Alternatively, consideration should be given to fitting
polyamide or polymer liners to contact surfaces. Roller fairleads should be well maintained and
kept free to rotate.

Section 6

The use of steel wire mooring ropes or towing pennants on contact surfaces such as fairleads
and rollers which are intended for use with high modulus synthetic fibre mooring ropes will cause
damage and is not recommended.

The use of anti-chafing gear will prolong the service life of high modulus ropes but may be difficult
to manage in service.

6.4.7.3 Mooring Winches

High modulus synthetic fibre ropes are commonly used on winches in the same way as steel wire
ropes. If steel wire rope is substituted with a larger diameter high modulus synthetic fibre rope, it
may not be possible to stow the same length on the winch stowage drum. In assessing drum
capacity, the following formula may be used:

A, B, C and D: reel sizes in cm

d = rope diameter in mm
L = rope length in m

Spooling capacity ‘L’ =

x π x 0.9

C x D x (B + C)

The minimum drum diameter should be at least 16 times the design rope diameter.

High modulus synthetic fibre ropes have a lower coefficient of friction than steel wire ropes and
the securing arrangements of the rope to the drum will need to be checked. In addition, more
turns on the tension drum may be needed to compensate for loss of grip. Fibre ropes also have a
tendency to "bury" under tension, therefore more than one layer of turns on the tension drum
should be avoided where possible.

To avoid chafing in the transfer section between the storage drum and the split drum it is
important to pay attention to the faring of the edge. One solution is to alter the fairing as indicated
in Figure 6.6 (A-C).

FIGURE 6.6A: FAIRING OF SPLIT DRUM EDGE

Note: 0.9 = 10% allowance in case of erratic spooling

Section 6

FIGURES 6.6 B & C: FAIRED SPLIT DRUM EDGE

6.4.7.4 Fatigue and Service Life

In general, all fibre and steel wire ropes fatigue over time. Life expectancy is determined by a
number of factors such as safety factors, D:d ratios (Diameter of the rope : Bending diameter)
and the condition of contact surfaces. It has been shown that a small increase in safety factor can
result in a significant increase in service life.

Tension/tension fatigue of high modulus fibres is good when compared with steel wires. The
construction of high modulus ropes will determine the rope’s susceptibility to torsional fatigue.

Bend fatigue will be impacted by load levels and the diameter of contact surfaces. High modulus
ropes generally require a larger bend radius to achieve the same fatigue life as steel.

6.4.8 Inspection and Removal from Service

Further guidance on inspection and removal from service is given in Appendix D.

6.5 SYNTHETIC TAILS

6.5.1

General

In order to provide additional elasticity, the wire and high modulus mooring lines of some large
ships are fitted at the shore end with a tail or pendant. The additional elasticity provided by the
tail reduces the dynamic loads induced in the mooring line by allowing the ship to respond more
closely to various combinations of wind, wave and current, as well as to ships passing nearby.
Tails also tend to distribute the loadings more evenly among mooring lines in the same service.
However, if the tail is too elastic the ship movement may be in excess of that which can be
tolerated by the terminal's cargo transfer system.

Any material having moderate to high elasticity is suitable for the manufacture of tails. Common
materials include polyester, polyester/polyolefin composites and polyamide. To increase fatigue
life and strength, it is recommended that tails are torque matched to the main line.

The fatigue life of the mooring line/tail combination can be prolonged by the appropriate choice of
both material type and elasticity of main line and tail components.

Fatigue analysis is an important tool to assist in the selection, safe operation and retirement of
mooring lines and tails. Due to cyclic loading, tails are subjected to a high rate of fatigue resulting

Section 6

in reduced strength with use. Tests conducted on failures have revealed that tails can undergo a
substantial reduction in breaking strength in a relatively short period of time. Careful
management is required to ensure that the integrity of the mooring configuration is not
compromised.

Synthetic tails should have an MBL at least 25% higher than that of the mooring line to which it is
attached. Polyamide tails should have a 37% higher MBL than the mooring line to take account
of loss of strength when wet.

Some dedicated lightering ships may be equipped with special mooring line arrangements such
that the synthetic tail may be of a particular length and be positioned outside the ship’s fairleads
with a further wire pendant attached to its end to prevent chafing damage.

6.5.2 Tail Length

The traditional tail length of 11 metres is adequate for sheltered pierside moorings where little or
no wave induced vessel motions occur. For very high tidal ranges, it may lead to excessive line
tending which, if not conducted properly, could lead to lines overloading and poor load sharing.
In this situation, the use of longer tails should be assessed as they may provide a safer mooring
system that also requires less tending.

At exposed pierside moorings where significant ship motions occur, the tail length of 11 metres
may be inadequate. This could lead to immediate tensile failure, or in the longer term, lead to the
fatigue failure of main winch ropes and/or mooring equipment on board or ashore.

For large ships, longer tail lengths up to 30 metres may be required for the most harsh conditions,
where waves up to 2m significant wave height and having periods in excess of 10 seconds may
be encountered.

Increased tail length will typically only be required for breast lines and may not be necessary for
springs lines. Most wave induced motions are transverse in nature and hence wave induced ship
motions at the chocks or fairleads of springs lines are minimal.

Studies have demonstrated that ship excursion is not directly proportional to increased tail length
for the component of wave induced ship motion. For example, increasing the tail from 11m to
33m may lead to approximately a 20% increase in ship movement.

In summary:

•  Longer tail lengths reduce line loading.
•  Longer tail lengths increase fatigue life.
•  11m tail lengths may not be suitable for exposed berths.
•  Use of more elastic tail materials can increases main line life due to decreased line loads.

6.5.3 Retirement Criteria

Tails should be replaced at least every 18 months unless experience, hours in use coupled with
inspection indicates a longer or shorter period is warranted. A record of service should be
maintained that includes time in use and inspection results.

Destruction testing of used tails may be of assistance when determining suitable replacement
intervals. Tails should be replaced prior to their residual strength falling to 60% of their original
MBL.

6.5.4

Methods of Connecting Tails

Tails should be connected to a wire mooring line using appropriate shackles, for example, those
manufactured by Mandal, Tonsberg and Boss. The SWL of the joining shackle should be equal
or greater than SWL of the mooring lines to which they are attached.

Section 7

Section 7

Winch Performance, Brake Holding

Capacity and Strength Requirements

7.1 FUNCTION AND TYPE OF MOORING WINCHES

Mooring winches perform a multitude of functions. They secure the shipboard end of mooring
lines, provide for adjustment of the mooring line length to suit the mooring pattern in each port
and compensate for changes in draft and tide. They serve to store the mooring line when not in
use and to haul the ship into position against environmental or inertia forces. They also act as a
safety device that releases the line load in a controlled manner once the force in the line
increases to pre-set levels. General requirements for shipboard mooring winches are dealt with
in ISO Standards 3730 and 7825.

Winches can be categorised by their control type (automatic or manual tensioning), drive type
(hydraulic, electric or steam), by the number of drums associated with each drive (single drum,
double drum, triple drum), by the type of drums (split, undivided) and by their brake type and
brake application (band, disc, mechanical screw, spring applied). Each of these features
influences the mooring winch function and will be briefly discussed below.

Although winch drives serving double drums are common on many ships, caution is advised
when considering the fitting of triple drums owing to the potential impact of a failure of a single
drive on overall mooring capabilities.

7.1.1

Automatic Tension Winches

Automatic tension winches are designed to automatically heave-in whenever the line tension
falls below a pre-set value. Likewise, they will pay out if the line tension exceeds a pre-set value.
Because of the possibility of tension winches operating in an uncontrolled manner, resulting in
ships being 'walked' along the pier, they should never be operated in the automatic mode when
the ship is connected to the shore cargo manifold. Moorings should be secured with the winch
drum held on the manual brake and with the winch out of gear.

7.2 WINCH DRUMS

Winch drums may be either split or undivided. The split drum is composed of a tension section
and a line storage section. It has the advantage that it can maintain a constant brake holding
capacity and heaving force, due to the fact that the mooring line is always run off the first layer of
the tension drum. For this reason, split drum winches are preferred by most operators. The
disadvantage of the split drum is the more difficult operation, a factor which can be overcome
with proper instructions and operator experience. Another reason for their use is that ISO
Standard 3730, Annex A, recommends that synthetic ropes under tension should not be wound
on a drum in more than one layer or short life will result, and this can normally only be avoided
by using split drums.

For either type of drum, the minimum drum diameter should be 16 times the design wire rope's
diameter, see Section 6.2.4. For conventional and high modulus fibre ropes, the manufacturer
should be consulted for information on the acceptable minimum bend radius for specific
applications.

Split drums should be wide enough to allow for 10 turns of the design wire rope on the tension

Section 7

In operation, the mooring line from the split drum winch is sent ashore, either directly from the
storage section or first from the working section and then from the storage section. As the line is
recovered, it is wound directly on the storage section until that time when only sufficient slack is
available to provide a sufficient number of turns on the tension section to: (1) hold the tension of
the line on the tension section only and (2) provide extra turns to allow for adjustments of the line
throughout cargo transfer. At that time the mooring line is fed through the slot from the storage
section to the tension section .

The transfer of the mooring line from the storage section to the tension section is difficult to
judge, particularly when long drifts of line are used such as at multi-buoy moorings. Care must
also be exercised to prevent tension coming on the line during the transfer at the time when it
passes through the slot. If this is not done, such tension could cause damage to the line or injury
to personnel involved in the transfer. There is also concern that the mooring operations could
take longer, especially when excessive layers develop on the tension section. The delay occurs
because steps must be taken prior to completion of mooring to correct the number of turns on
the tension section.

7.2.2 Undivided Drums

The undivided drum winch is commonly found on smaller ships and is preferred by some
shipyards, mainly in Japan, for VLCCs. The undivided drum avoids the need to transfer the
mooring line from section to section as is required for a split-drum winch when a poor estimate
has been made of the spooling requirements. The undivided drum eliminates the potential for
line damage and personnel injury that exists at the time of transfer on a split drum.

However, if this type of drum is selected, the operator should be aware that it is often difficult to
spool and stow the mooring line on the drum satisfactorily. If the line is not spooled properly, it
can be damaged when tension is applied to the system. To reduce this problem, care should be
exercised in the location of the winch. It should be placed a sufficient distance from the fairlead
to ensure that the mooring line can be properly spooled. Reference should also be made to
Section 3.15.

7.2.3 Handling of SPM Pick-up Ropes

Ships likely to trade to SPM's should be equipped to safely handle SPM pick-up ropes taking into
consideration safety and protection from risk of snapback injury to mooring personnel. (Refer also
to Appendix E).

Wherever possible, winch storage drums used to recover the pick-up ropes should be positioned
to enable a direct straight lead with the bow fairlead and bow chain stopper without the use of
pedestal rollers. This relative positioning of the tanker SPM mooring equipment in a direct straight
lead is considered the safest and most efficient arrangement for handling the pick-up ropes.
However, recognising not all mooring arrangement designs will permit a direct straight lead to a
winch storage drum, pedestal rollers may need to be utilised.

Personnel safety considerations should take priority when determining the number and position of
pedestal rollers. It is essential that the pedestal roller(s) are correctly positioned relative to the
winch drum and the centre of the bow chain stopper to enable a direct lead from the centre of the
bow fairlead to the centre of the bow chain stopper and to allow the pick-up rope to be stowed
evenly on the storage drum. There should be at least 3.0 m distance between the aft side of the
bow chain stopper and the closest pedestal roller to allow for the pick-up rope eye, connecting
shackle, shipboard end oblong plate and a number of chafe chain links. The number of pedestal
rollers used for each bow chain stopper should not exceed two and the angle of change of
direction of the pick-up rope lead should be minimised.

Winch storage drums used to stow the pick-up rope should be capable of lifting at least 15 tonnes
and be of sufficient size to accommodate 150 metres of 80mm diameter rope. Use of winch drum
ends (warping ends) to handle pick-up ropes is considered unsafe and should be avoided.

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