CONTENTS

1 Introduction
1.1 Training other crew members
1.2 Preparing a training session
1.3 Running a training session

2 Theory of mooring
2.1 The forces acting on a moored ship
2.2 Mooring lines
2.3 Materials and properties
2.4 Strength and elasticity
2.5 Mooring equipment
2.6 Printed guides and electronic aids to mooring

3 Further information and reading

4 Appendices
4.1 Steel wire ropes
4.2 Synthetic fibre ropes
4.3 Rope over strength
4.4 Case studies
1 INTRODUCTION

This training package, Theory of Mooring, is Part 1 of the Mooring Series and consists of
this Reference and a video programme. The other titles in the series are:
Part 2: Safe Mooring Practice
Part 3: Maintenance of Mooring Systems

The training is intended for seafarers sailing on all types and sizes of vessel and is
primarily aimed at those crew members forming a mooring party to help berth a vessel
safely and efficiently. Although the types and positions of mooring equipment can vary
on different vessels, this training package sets out the ‘best practice’ mooring
procedures which should apply to any ship, port or terminal.

User guidance – main points

· The programme may be used by individuals, or in small groups for training.
· It is essential to work through the programme systematically and NOT to jump
any section.
· Do not proceed to the next topic until everything watched and read has been
understood.
· If something is not understood, replay the video section, read the relevant part of
the Reference again or consult a senior officer.
· To fully understand the contents it will usually be necessary to watch the video
more than once as well as re­reading the Reference.

1.1 Training other crew members

If you are responsible for training others then you should aim to follow the instructions in
this section as closely as possible. It will help you to learn how to run effective training
sessions with the crew.

Read this Reference before watching the video. Make sure you understand it. Next,
watch the video all the way through. Where possible the information in this training
package should be related to your own vessel’s mooring equipment. Make sure you fully
understand every aspect of the safe mooring procedures described. Learn everything
you can about your own vessel’s mooring equipment using the manufacturers’ relevant
operating and safety manuals. There is a lot of information contained in this package so
more than one training session may be required.

Most importantly, ensure that you have a copy of your company’s Mooring Policy, the
appropriate section from your vessel’s Operating Procedures for reference and a copy of
your vessel’s own Mooring Plan.
1.2 Preparing a training session
During each training session you will need pens and notepads and somewhere to
write/draw, such as a flipchart, and different coloured marker pens, whiteboard or similar.

Have samples of different types of mooring line in use on board your vessel. If possible
have samples of other wire and synthetic lines the crew may have to handle on other
occasions.

Use examples of frayed or damaged lines, or other defective items of mooring

equipment, such as a part of a winch kept from a previous repair, or a worn winch brake
lining. You may also have examples of other items used in mooring, such as stoppers,
correctly and incorrectly spliced lines, and so on.

1.3 Running a training session

Setting the scene
Tell the crew members what the training is about, how it will be run (timing, expected
interaction, practical work, etc.) and what you will expect of them once they have
completed it. Make sure they understand there will be a test at the end to check their
understanding of the session.

Getting their full attention

Ask your audience to share their experiences of any previous mooring related accidents
or ‘near misses’ they may have witnessed or have been involved in. These anecdotal
accounts are very effective at promoting good interaction within a group and can usefully
make everyone feel more involved and at ease with the training session.

It can be easy to get distracted by a new or interesting port, thoughts of a hearty meal
and a nice warm bed, or mail from home. Explain that often it is during short moments of
distraction while engaged in mooring operations that many seafarers have been injured
or killed.

Using the Case studies

These are in the Appendices and you should photocopy those you think are most
relevant to your crew members and hand them out. Ask your group to focus on the
areas they think are most critical in each case. Be prepared for differing views and
always encourage everyone to participate.

Begin by discussing the many sorts of things which can go wrong and may cause
accidents during mooring operations. Ask the group to discuss whether any of the
accidents described in the case studies could or have ever happened to them.

Showing the video

Show the video all the way through to the end. If you have time, run it once more, but
this time pause after each scene or part of the mooring procedure and ask your
audience to discuss what they have just seen. Use the information and diagrams in this
Reference to help you direct and broaden the discussion.
Encouraging discussion
The trainer can encourage discussion by asking leading questions, for example:
· How does the equipment on your vessel differ from that shown in the video?
· Were the mooring operations in the video carried out differently to your own
vessel?
· Have you seen such tasks carried out dangerously on board?
· Why do you think individuals carry out mooring tasks dangerously?

Practical training
Practical training can give a better understanding of safe mooring procedures and are
best carried out on deck. Examples are:
● visual inspection of mooring lines for wear and tear
● marking out the snapback zones and potential danger areas around each winch
● identifying deck and winch operator blind spots
● examining winches for signs of potential maintenance defects

How much information does the group need?

Some sections of this Reference go into a lot of detail about equipment and procedures
for mooring. For example, there is a lot of information about the construction and
properties of different types of mooring lines in Appendix 1. Do all your crew members
need to know about each of these aspects of mooring operations? It is for you, the
Trainer, to decide. Each group will vary as to how much they need to learn to be able to
carry out their mooring duties efficiently and safely. You can tailor the information
provided to suit your requirements.

Checking everyone has understood

At the end of the training session use the Tutorial and Test with the group and get them
to answer the questions. Check the answers to ensure everyone has fully understood
everything. If you think that the score achieved in the test is too low, then you should go
back over those parts which have not been understood. Finally, don’t forget to record
details of all training sessions in your company’s SMS as required by ISM.

Further Information and reading

All crew members should be encouraged to read the documents in their on board library.
Not all those listed in Section 3 will be available but every opportunity should be taken to
update knowledge and understanding where possible. Remember, although a book may
be written by an oil related organisation such as OCIMF, much of the information it
contains will be relevant whatever type of vessel you are sailing on.
2 THEORY OF MOORING
Effectively and safely mooring a ship at a berth requires a basic understanding of the
theory of forces acting on a ship, how those forces are applied to mooring lines and
equipment and the best mooring arrangement for a particular ship at a particular berth.

To understand this theory in relation to your own ship, it should be read in conjunction
with additional material such as the company’s Mooring Policy, a copy of your ships
Mooring Plan and your own ship’s Operating Procedures.

2.1 The forces acting on a moored ship

A ship’s moorings must resist the forces due to some or possibly all of the following
factors:
● wind
● tide and currents
● waves and swell
● surge from ships passing close by
● changes in draft, trim or list

Although other factors such as ice may be encountered alongside, and can produce
considerable loads on a moored ship, the main environmental factors considered here
are wind, current and tide.

The mooring system on ships trading worldwide should be sufficient to satisfy the
following Standard Environmental Criteria:

60 knots of wind from any direction simultaneously with

a 3 knot current from ahead or abeam

or
a 2 knot current at 10o or 170o

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

These criteria are intended to cover conditions that could be encountered on worldwide
trade; however they cannot possibly cater for the most extreme combination of
environmental conditions at every berth where additional moorings, sometimes shore
based, will be provided. When considering mooring arrangements at a particular port it is
vital that all necessary publications are consulted in order to be aware of any extreme
local conditions that may exist.

Operating Procedures to satisfy these changing environmental conditions are discussed

further in Part 2 of this series, Safe Mooring Practice.
Wind
Due to the decrease in friction from land or sea, wind speed and force increases with
height above sea level. For example, a 30 knot wind at sea level can be much stronger
at deck level. Consequently larger, high freeboard ships are more susceptible to strong
winds.

High sided ships such as car carriers, those with changing and sometimes high
freeboards such as large tankers or dry bulk carriers and high standing deck cargo are
therefore more susceptible to increases in wind speed.

Currents
In the majority of cases currents flow more or less parallel to terminals or berths thereby
minimising the effect on a ship. However, a current with only a small angle off the bow,
say five degrees can create a considerable transverse force.

Current forces must be added to that of the wind when considering mooring
arrangements and are compounded by the significant effect of low under keel clearance
as shown in Figure 1.1.

Figure 1.1: Effect of underkeel clearance on current force

The large difference between current forces from ahead and abeam can be illustrated by
the results of model tests on a loaded 250,000 dwt ship with an under keel clearance of
2m:

· Current force created by a 1 knot head current = about 5 tonnes (49kN)

· Current force created by a 1 knot beam current = about 230 tonnes (2256kN)

Normally, current force becomes important in mooring only when a number of factors
combine, the most important of which are:
 ● the ship has a deep draft
● the current is from abeam, and
● there is minimal underkeel clearance

In this situation, the beam current will be forced around the ship’s bow and stern and
increase in speed as it passes under the keel. The effects could be significant and have
to be considered during mooring procedures.

Combined forces
Forces exerted by wind/current are proportional to the square of their speed. For
example, the force of a 60 knot wind is four times greater than that from a 30 knot wind.
Similarly, the force from a 3 knot current is nine times greater than that caused by a 1
knot current. As such it is important to take early action to supplement a ship’s mooring
arrangement, as small increases in speed can have a large increase in force.

Figures shown in the following table are indicative only of forces exerted transversely
and longitudinally on different sized ships. They illustrate the significant increase
between light (ballast) and loaded conditions.

Again, it should be emphasised here that high sided ships and those with high deck
cargoes will always be subject to higher environmental loads.

Transverse forces Longitudinal forces

Tonnes Tonnes
Summer DWT Wind Current Wind Current
18,000 loaded 33 30 27 15
ballast 102 7 48 5
70,000 loaded 72 62 37 35
ballast 210 8 52 13
200,000 loaded 106 132 49 73
ballast 378 15 76 23

Table 1: Examples of the force a 60 knot wind and 3 knot current can exert on various
sized ships

Tide
The rise and fall of tide causes a ship to move vertically at a berth. The effect will be
changing tensions and angles (referred to as dip) in the mooring lines. In ports with a
large tidal range, you should check the tide tables and inspect the lines regularly to
ensure the ship is safely moored at all times.

Surge, waves and swell

The effects of waves and swell and the surge from passing ships are difficult to predict.
Local advice must be obtained as the forces created by these effects can be significant
and may put an excessive strain on the mooring system.
It is particularly important to take additional measures with your mooring system if your
vessel is fully loaded, has a deep draft with little underkeel clearance, and is moored
close to a shipping lane. In such circumstances there is a danger of particularly heavy
surge from a passing vessel forcing your ship away from the berth. In extreme cases this
could cause mooring lines to part, resulting in damage to the vessel, the berth and shore
installations and personal injury.

Cargo and ballast

Changing displacement during cargo operations alters both draft and trim, changing a
ship’s susceptibility to environmental forces. These changes must be constantly and
carefully monitored, so that any necessary adjustments can be made to the mooring
system.

2.2 Mooring lines

General arrangement
To resist the forces detailed above, and to keep a ship safely positioned alongside a
berth, mooring lines are connected between the ship and berth. Made from a variety of
materials, construction and sizes, the geometric arrangement of lines is sometimes
referred to as the mooring pattern.

For general applications, the deployed mooring pattern must be able to resist
environmental forces from any direction. As a general principle, these forces can be split
into longitudinal (along the berth) and transverse (off the berth) components, the
mooring lines required to effectively resist them known as spring, breast and head and
stern lines.

Due to the variation between different shore facilities and differing environmental
considerations it is rarely possible to deploy moorings in an ideal direction. In practice
therefore, as well as breast and spring lines, a ship’s mooring pattern would normally
incorporate head and stern lines. Depending on the dominant force at a particular berth,
increased numbers of lines from a particular direction may be required.

The effectiveness of a particular mooring line is influenced by the vertical angle between
line and jetty and the horizontal angle the line forms with the parallel side of the ship.
The ideal arrangement is that shown in Figure 1.2. The more that lines depart from this
ideal arrangement, the less effective they are in restraining the vessel as required.
 Figure 1.2: Ideal restraint arrangement

Figure 1.3: A short mooring line from a ship to a bollard close to and below the fairlead
loses much of its holding power

Ideally, a mooring pattern should satisfy the following:

· Mooring lines arranged symmetrically about the midship point of the ship
· Breast lines orientated as close to 90o as possible to the ship’s centre line
· Spring lines orientated as parallel as possible to the ship’s centre line
· The vertical angle of mooring lines kept to a minimum
· Mooring lines of the same size and material used for all leads
· The same size and type of synthetic tails used in the same service

2.3 Materials and properties

Mooring lines are manufactured from a number of different materials. Ship designers
and operators will take account of various factors from ship size to cost when outfitting a
ship with the most appropriate lines and equipment.

Modern day line/rope materials can be divided into three main groups. Wire, high
modulus (synthetic) fibre, and conventional synthetic fibre. Each group has different
main properties as outlined below. However, the most important and common factor
they all share is known as the line or rope’s Minimum Breaking Load (MBL). For any
individual rope, this value is found by testing to destruction a sample of that line.

MBL is defined as the minimum load that a new rope will sustain before breaking
when tested to destruction.

MBL is a critical factor used by ship designers when selecting mooring equipment,
mooring layout and winch brake loads/settings. The MBL of all ropes supplied is stated
on the rope’s certificate and should be made known to all personnel involved in mooring
activities.

Wire
Ø High strength
Ø Low stretch
Ø High maintenance
Ø Heavy and difficult to handle

High modulus fibre

The term ‘high modulus fibre mooring lines’ generally refers to ropes made from high
modulus fibres such as ‘Aramid’ and High Modulus Polyethylene (HMPE).
Ø High strength
Ø Low stretch
Ø Low maintenance
Ø Relatively light and easier than wire to handle

Conventional synthetic fibre

Ø Relatively low strength
Ø High stretch
Ø Low maintenance
Ø Light and easy to handle

In general, larger vessels are equipped with either wire or high modulus fibre mooring
lines fitted to self­stowing winches, whereas smaller vessels tend to be equipped with
conventional synthetic fibre lines, also on self­stowing winches.

2.4 Strength and elasticity

The two most important mooring line properties are strength and elasticity. The ‘strength’
of a line refers to the load or weight it will take before it parts. For a particular mooring
line, theoretically this is known as the MBL. This is a critical factor as it determines the
settings of the winch brakes and types and size of associated on board mooring
equipment.

The elasticity of a mooring line is a measure of its ability to stretch under a given load.
An elastic line will stretch more than a stiff one. A line’s elasticity depends on the
material it is made of, its length, and diameter.
Most importantly, when comparing the different rope types above, it should be noted that
wire mooring lines are very stiff compared to conventional synthetic fibre lines. For
instance, if a wire mooring line was to be run parallel to a conventional synthetic fibre
line, the wire would carry almost the entire load. Typically, the elongation of a 6 x 37
construction wire line under load is about 1% of wire length, whereas a polypropylene
rope may stretch more than 10 times as much. Although a synthetic material, HMPE
ropes or similar have much less elasticity than conventional synthetic fibre lines and if
run in parallel, would also carry most of the load.

The effect of line length must also be considered. Elasticity varies directly with line
length. For example, a wire 60m long would stretch more than an equivalent size wire of
30m. The effect of this would be a reduced holding capacity on the longer wire.

For these reasons, as a general rule, mixing lines of differing size, construction material,
and length in the same service (spring, breast or head and stern lines) should be
avoided.

Figure 1.4(a) and Figure 1.4(b) demonstrate the strains on lines of different materials
and lengths being used alongside each other.
The widely varying performance and characteristics of the many different types of wire
and synthetic mooring lines are set out in more detail in Appendix 1 of this Reference.

2.5 Mooring equipment

Mooring equipment includes the many items found on board a ship which together are
designed to hold a ship safely alongside a berth or to another ship.

Note ­ Anchoring equipment is not included here but further information can be found in
the Videotel programme Anchoring Safely.

A number of factors must be taken into consideration when ship designers and
operators select mooring equipment. Perhaps the most important factor is the MBL of
the particular mooring lines needed to safely restrain that size of ship.

To better understand this, although the safe working load of a particular item of
equipment will be equal to the MBL, in service, the line tension at any one time is
unlikely to be more than 20% of its MBL. This allows for factors of safety and the fact
that any particular line will not be always deployed in the ideal way or direction.
For more detailed information on design loads, safety factors and strength of mooring
equipment, the reader is advised to consult other publications such as the OCIMF
Mooring Equipment Guidelines Edition 3 (MEG 3).

Considered to be at the heart of any mooring system, this Reference deals only with the
mooring winch and its relationship with the mooring line(s) it controls.

The mooring winch

Winches perform a number of different functions and are generally powered by electric
or hydraulic motors. Winches are often the securing point for a line’s shipboard end and
can be used to store, deploy, recover and adjust mooring lines. A winch may also act as
a safety device by releasing a line under load in a controlled manner (render) once the
force in that line reaches a pre­set level.

Winch drums
In many modern ships today, mooring lines are permanently stored on the winch drum
and, for any given arrangement, remain on the drum when the vessel is safely moored
and ‘all fast’ alongside. Any additional lines, for example to deal with extraordinary
environmental conditions or to meet a shore request, are made fast on the ship’s bitts.
These ropes would be tensioned on the winch drum end and transferred to the bitts
using a chain or rope stopper.

Under no circumstances should a mooring line be made fast to equipment not

designed for that purpose. This includes the ‘drum end’ of a winch.

There are two main types of winch drum, ‘undivided’ and ‘split’. Although there are
advantages and disadvantages in both systems; the split drum has one main advantage.
When properly deployed, the mooring line is always run off the first layer of the tension
drum, thereby maintaining a constant and effective brake holding capacity and heaving
force.

Figure 1.5: The split drum winch

The drum consists of a tension section and a separate storage section divided by a
notched flange. Properly deployed, the winch operates with one layer of line only on the
tension section maintaining a constant and effective holding power. The main
disadvantage of split drums is the increased operational difficulty when making a line
fast. Care must be taken when transferring the line from storage to tension section in
order to avoid injury.

Operation of a split drum with more than one layer will decrease the brake holding
capacity and thereby the effectiveness of the mooring system.

Undivided drums
Their main advantage is ease of handling. However, they have one major disadvantage.
Poorly stowed ropes under tension may not have the correct holding power and are
sometimes subject to severe abrasion and subsequent damage under tension.
Undetected, this damage could later put handlers’ lives at risk.

Badly stowed lines on an undivided drum can lead to excessive loads increasing the
possibility of mooring line failure. This occurs because a winch brake’s holding power
depends on the number of layers of line on the drum. Holding power decreases as
layers on the drum increase.
 Figure 1.6a: Single line on the first layer of a drum, brake holding power is 55 tonnes

Figure 1.6b: 4 layers of line on the drum, brake holding power reduced to 40 tonnes

Winch brakes
The winch brake secures the storage drum and hence the mooring lines at the
shipboard end. It also acts as a safety device by rendering a line under extreme load
before it breaks. Winch brakes can be set to render at different loads. Therefore, it is
vital that the brake is set at the correct level. This is normally 60% of the relevant
mooring line’s MBL.

The most common type of brake is the band brake, see Figure 6a and Figure 6b.
Modifications of this type of brake are the spring applied brakes either with hydraulic or
manual setting and release. A relatively small force is required to hold a high mooring
load. However there are disadvantages. Improper brake settings, incorrectly stowed
lines and poor maintenance, all tend to reduce the efficiency of the brake.

Some hydraulic winches and most electric winches use spring applied disc brakes direct
to the drive motor. They are easier to operate but once a ship is ‘all fast’ should be
declutched and the line held only on the primary (band) brake.
Figure 1.7: Typical band brake arrangement. Note – Rope always pulls against the fixed
or anchored end of the brake

The primary brake on a winch should be set to prove that it will render at a load that is
equivalent to 60% of the line’s MBL. However, it should be noted however that as the
efficiency of a brake deteriorates during service, it may be prudent to set a new winch
brake’s capacity to more than 60% up to a maximum of 80% of MBL.

Winch brake testing

The relationship between a mooring line’s MBL and the setting of a winch brake is
crucial to the safe operation of a winch. Winch brakes should be tested annually or after
any major modification, including a change of mooring line material or size.

Prior to testing a brake, all areas of the winch must be checked and confirmed to be fully
functional. The main purpose of the test is to ensure the brake will render at a load less
than the appropriate line’s MBL. The procedure for testing a winch brake is dealt with
more fully in Part 3 of this series, Maintenance of Mooring Systems.

Winch performance
The operating parameters for winches on a particular ship are derived from the size of
mooring lines needed to restrain that ship at a berth. The mooring line MBLs are a factor
of ship size, the calculation of mooring forces and mooring restraint requirements.
Together these factors determine the ideal MBL for all lines which in turn leads to the
following winch design parameters:

· Brake design load = 80% of line MBL

· Brake holding load = 60% of line MBL
· Winch pull = 22­33% of line MBL
· Drum diameter = 16 x line diameter
· Width of tension drum = 10 x line diameter

The winch’s performance can now be calculated and will determine such factors as the
speed a line can be deployed and recovered, the drum capacity, the rated pull and most
importantly, the Stall Heaving Capacity or stall pull. This is the pull exerted on a line
when the winch control is in the heave position and the line is held stationary. A high
capacity is required in order to be able to heave a ship alongside a berth. However, in
practice, it should not be so high that there is any danger of a line breaking and should
never exceed 50% of the line’s MBL.

Remember ­ a winch brake’s holding power on the brake is always greater than its
heaving power. If a winch brake starts to render, or slip, it will be impossible for the
winch drive to heave in by releasing the brake unless whatever is causing the excessive
load is reduced.

Self­tensioning winches
Some vessels are fitted with self­tensioning or automatic tension winches. They are
designed to automatically heave in whenever a line tension falls below a set value or
slack away if the tension exceeds a set value. Whilst these winches reduce the work
load in port, it is recommended that, especially when connected to a shore manifold or
working to close longitudinal limits, they should only be used in the manual mode to
prevent a ship from walking itself along or off a berth. Secure all lines with the winch
drum held on a manual brake and the winch out of gear.

Figure 1.8: A vessel unintentionally shifting at its moorings can cause hoses or loading
arms to break, possibly resulting in pollution or costly damage
Reeling
Reeling lines onto a drum in the wrong direction can cut the brake holding power by up
to 50%. If they have not been marked by the manufacturer with the correct reeling
direction, they should be clearly marked ‘HEAVE IN’ and ‘SLACK OUT’.

Winches fitted with disc brakes do not have to be marked as they cannot be reeled in
the wrong direction.

2.6 Printed guides and electronic aids to mooring

Most busy ports and terminals have their mooring arrangements and other details set
out in publications such as Guide to Port Entry. As well as these aids, many vessels
now have electronic chart systems, and nearly all of these will contain detailed diagrams
showing port layouts, navigational aids and moorings, and other port facilities. However,
electronic charts may not be sufficiently accurate as the primary means of manoeuvring
the ship to its berth so should be used with caution when approaching and entering port.

CDs are increasingly available showing port layouts, navigational aids, mooring
arrangements and other port facilities. Many of the world’s larger ports also have their
own websites which can provide information on port layout, directions for navigation and
positions of navigational aids, Notices to Mariners, tidal information, special instructions
about anchoring, and regulations concerning such matters as explosives and LPG/LNG
vessels, as well as information about moorings and other port facilities. Charts showing
port layouts and information about facilities and procedures are also commercially
available on the websites of nautical publishers. These can be accessed from the
Internet.

3 FURTHER INFORMATION AND READING

Ø Code of Safe Working Practice for Merchant Seamen, UK Maritime and
Coastguard Agency (MCA)
Ø Effective Mooring, Oil Companies International Marine Forum (OCIMF)
Ø Guide to Port Entry
Ø Guidelines and Recommendations for the Safe Mooring of Large Ships at Piers
and Sea Islands, Oil Companies International Marine Forum (OCIMF)
Ø Guidelines on the Use of High Modulus Synthetic Fibre Ropes as Mooring Lines
on Large Tankers, Oil Companies International Marine Forum (OCIMF)
Ø Harbour Masters Report
Ø International Safety Guide for Oil Tankers and Terminals (ISGOTT)
Ø Mooring and Anchoring Ships Vol 1 & 2, Nautical Institute
Ø Mooring Equipment Guidelines, Oil Companies International Marine Forum
(OCIMF)
Ø Mooring Guidebook
Ø Recommendations for Equipment Employed in the Bow Mooring of Conventional
Tankers at Single Point Moorings (OCIMF)
Ø Recommendations for Equipment Employed in the Mooring of Ships at Single
Point Moorings, Oil Companies International Marine Forum (OCIMF)
 Ø Tug Guide

Related Videotel titles of interest

Ø 5 x Security Videos Series:
­ Recognising Suspicious Behaviour – code 933
­ Recognising Proper Forms of Identification – code 934
­ Search Techniques – code 935
­ Identifying Explosives and Weapons – code 936
­ Crowd Control – code 937
Ø Anchoring Safely – code 928
Ø Coping with Stowaways – code 652
Ø Safer Mooring – code 997
Ø The Cold and Heavy Weather File – code 626
Ø Working with Tugs – code 972

4 APPENDICES

Ships are equipped with mooring lines made of the material most appropriate to their
size and trading pattern. The most common materials are wire and man­made synthetics.
The latter can be divided into two main groups; conventional synthetic and high modulus
fibre, often referred to as HMPE.

It is critical that seafarers working with mooring lines are aware of their main properties
and specifications, in particular Minimum Breaking Load (MBL).

4.1 Steel wire ropes

Makers of wire mooring ropes use their own standard terminology. This identifies how a
rope is constructed and some of its characteristics. Understanding these is important to
anyone handling wire ropes. The main characteristics are as follows:

Construction
Most wire mooring ropes are made of individual galvanised steel wires, twisted or laid
together to form a strand. A number of these strands are then laid up around a central
core to form a wire rope. The direction or lay of the wires, explained below, determines a
rope’s strength and flexibility.

A wire rope is defined by the number of wires in each strand and the number of strands
in the rope. So a 6 x 36 mooring line would have 6 strands, each made up of 36 wires
and an inner core.

Strands
Strands are constructed by laying individual wires around a central wire core. There are
two main methods, equal lay and cross lay as shown below.

Equal lay: when successive layers of wires are twisted over the preceding inner layers
at the same angle.
 Figure a: Equal lay construction of a mooring line. Size for size, wire ropes made of
equal lay are stronger than those made of cross lay

Cross lay: when successive layers of wires are twisted over the preceding inner layers
at increasingly greater angles.

Figure b: Mooring lines made of cross lay construction are more flexible but not as
strong as those made of equal lay

A wire rope is finally constructed by laying several strands together around a central
fibre or wire core. Wire ropes with a fibre core are more flexible but not as strong as
ropes with a wire core.

Figure c shows cross sections of mooring wires with fibre and wire cores, six strands of
36 wires and 41 wires respectively.

Figure c: Cross sections of typical mooring wire ropes

Lay
The lay of a wire rope is the direction of the wires or strands that go into the construction
of that rope, termed left or right hand lay.

Ordinary Lay: when the lay of the wires making up the individual strands is in the
opposite direction to the lay of the strands making up the wire. Mooring wires are usually
constructed ordinary, right hand lay.
Lang’s Lay: when the lay of the wires making up the individual strands is the same
direction as the strands making up the wire. This construction is generally unsuitable for
mooring lines due to its instability and tendency to ‘unlay’.

Figure d: A left hand ordinary lay mooring line (left) and a right hand ordinary lay
mooring line (right)
Size
In addition to the number of wires used in their construction, a wire rope is measured
across its diameter; from the outer edge of a strand to the outer edge of the opposite
strand.

MBL
MBL is defined as the minimum load that a new rope will sustain before breaking
when a sample of that rope is tested to destruction. MBL is a critical factor used by
ship designers when selecting mooring equipment, mooring layout and winch brake
loads/settings. The MBL of all ropes supplied is stated on their certificate and should be
made known to all personnel involved in mooring activities.
 Figure e: The loss of breaking load when wire lines are bent around winch drums or
leads with small diameters

4.2 Synthetic fibre ropes

With the advent of modern synthetic materials, ship designers and operators have a
varied selection of materials to choose from. Synthetic materials fall into two main
categories: conventional synthetic and high modulus synthetic. The latter group is often
referred to as HMPE.

The use of synthetic mooring ropes at sea is widespread. It is important therefore that
seafarers thoroughly understand their different properties and the advantages and
disadvantages each may have. Understanding these differences could one day help
prevent an accident or save a life.

Construction
Synthetic lines are generally made up in one of two different forms. Hawser lay or plaited
lay.

Hawser lay ropes are not commonly used today for mooring as they can be prone to
kinking and can be difficult to handle. Instead, the most common constructions of
synthetic fibre lines are ‘8­strand plaited’ (sometimes called ‘square braid’ or ‘multiplait’),
and ‘double braid’ (sometimes called ‘braid on braid’).

Figure f: Hawser­laid Figure g: 8 strand, or square Figure h: Plaited inner line

Mooring lines, seldom braid uses a combination of with an outer sheath of
used left and right hand lays, is braiding of different
almost unkinkable and very material
flexible

Synthetic fibre lines are also available in a construction similar to wire lines, using six
strands of polyamide wound around a solid polyamide core. This construction, given
polyamide’s already high strength, provides an even greater MBL and lower elasticity
than most other synthetic lines of comparable size.
Recently available are other new forms of constructions of synthetic lines, designed to
provide even greater strength and reduced elasticity and for use in very specific
situations. The manufacturers’ specifications for these specialised lines should always
be checked to make sure their properties and MBL are appropriate for the task and
equipment they are planned for.

Rope type Weight Typical breaking Typical extension

(kg/100m) (tonnes) Load (at 50% breaking load)
Polyamide 265 72 12%
Polyester 328 67 10%
Polypropylene 185 47 9%
Polyester/polypropylene 242 58 14%
HMPE 184 240 1%
Aramid 293 160 2.5%
6­strand polyamide 245 81 16%

Table A1: Comparison of typical weight, breaking load and elasticity of an 8 strand,
64mm plaited rope made out of different synthetic fibres, against a 6 strand polyamide
rope

Diameter Polyamide Polyester Polypropylene Polyester/ Aramid 6 strand

(mm) Polypropylene Polyamide
40 30 27 19 24 73 31
44 36 33 23 28 88 42
48 42 38 27 33 105 50
52 49 45 31 39 123 54
56 56 51 36 45 145 66
60 64 57 41 50 163 74
64 72 67 47 58 185 81
72 90 83 58 72 232 114
80 110 103 72 88 290 135

Table A2: Comparison of typical MBL in tonnes of 8­strand plaited lines and 6­strand
polyamide line

Conventional synthetic fibre ropes

The four most common materials from which conventional synthetic mooring lines are
made are polyamide, polyester, polypropylene, and a mixture of polyester and
polypropylene. All have different properties and handling characteristics.

Polyamide
Polyamide is the strongest of the conventional synthetic fibre rope materials. It has been
widely used in marine mooring and towing since the 1950s. It has the lowest stiffness
modulus, and thus it is favoured where high extension (stretch) is required. When ropes
become wet they can lose up to 20% of their strength. Wet polyamide can also suffer
loss of strength from creep and internal abrasion from repeated heavy loading, generally
resulting in shorter service life.
o Advantages: high strength even with sustained loading
resistance to chemical attack from alkalis, oils and organic solvents
o Disadvantages:can be damaged by acids
high extension (stretch)
o Floats: No
o Melts at: 250ºC

Polyester
This is the heaviest of the synthetic fibre rope materials. Polyester mooring lines are
longer lasting than polyamide, and very strong polyester ropes are now being used
which are made from newer types of high­quality polyester fibres. Polyester ropes can
be as strong as polyamide when dry and do not lose strength when wet. Polyester ropes
are therefore favoured in many conventional marine applications.

o Advantages: lowest extension under load of all conventional synthetic fibres

o Disadvantages: not as strong as polyamide
relatively heavy
can be attacked by alkalis
o Floats: No
o Melts at: 230º – 260ºC

Polypropylene
The lightest of the conventional synthetic fibre ropes and comes in different grades.
Floats in water; ropes made of polypropylene were often favoured for this reason, and
also for their lower cost. However, polypropylene is weaker than either nylon or
polyester. Polypropylene rope can heat up and lose strength during high­speed cyclic
loading and may creep under high loads.

Mixtures
Polypropylene and polyester are sometimes combined in ropes. These hybrid ropes
have strength and stiffness properties similar to those of polyester ropes but with lower
weight and cost. Mixtures have greater resistance to surface abrasion and heat build­up
than polypropylene.

o Advantages: resists chemical attack by acids, alkalis and oils

does not lose strength when wet
moderately light and strong
high UV resistance
o Disadvantages: can be attacked by bleaching agents and some industrial solvents
o Floats: Yes
o Melts at: 170ºC

High modulus fibre ropes

HMPE
High Modulus Polyethylene (HMPE) has similar strength characteristics to steel wire and
is the strongest synthetic material commonly used in rope construction. However, it has
a relatively low melting point, and also has a tendency to creep and so can break at
sustained high loads. Nevertheless, HMPE does not suffer from axial compression
fatigue problems, has a low coefficient of friction, and has very good abrasion resistance.
HMPE is particularly highly resistant to acids, caustic soda, benzene and other
aggressive materials and contaminants.

Advantages: exceptional strength, equal to steel

highest strength­to­weight ratio of any synthetic fibre
highest abrasion resistance ratio of any synthetic fibre
low stretch
good fatigue resistance to tension, bending and abrasion
resists chemical attack
good flex fatigue resistance

Disadvantages: low melting point

more prone to mechanical damage than steel wires
high cost
susceptible to creep

Floats: Yes
Melts at: 150ºC

Aramid
This is the strongest of all the high modulus synthetic fibres and has the lowest
extension. Aramid was the first high performance fibre to be developed and was
introduced about 40 years ago. It was first used for mooring buoys, then later for deep
water platforms. Today it is used extensively for ships’ mooring systems particularly for
spring lines. Aramid fibres are made up of tiny crystal particles woven into individual
fibres which are then woven into mooring lines.

Advantages: exceptional strength, equal to steel

good resistance to mechanical damage
resists chemical attack
excellent strength­to­weight ratio
highest resistance to heat of any synthetic fibre material
Disadvantages: heavier than other synthetic material
not suitable for use in large braided or plaited lines
high cost
moderate­to­poor resistance to abrasion
difficult to splice
can suffer from fatigue leading to failure
Floats: No
Melts at: 260ºC

Vectran
A liquid crystal aromatic polyester (LCAP), is a more recent type of high modulus line,
mostly used at present by shore­based industries. It has better resistance to axial
compression fatigue and creep than Aramid, although it is also much more expensive
than either Aramid or HMPE. Now used in certain specific mooring applications,
generally where cost is not an overriding consideration.

PBO
A high performance synthetic fibre material that may be used to manufacture mooring
lines. PBO is very expensive, although it has even higher strength and higher modulus
than most synthetic fibre.

4.3 Rope over strength

Most conventional ropes lose strength during service. As a result their minimum
breaking load (MBL) will be reduced.

Some High Modulus fibre ropes however, can initially increase in strength during their
early service which in turn will increase their MBL. This could affect the performance of a
winch brake, especially if the selected setting is too high.

Normally, a winch brake would be set to 60% of a rope’s MBL. Should the strength of
the rope increase during the early part of its service, it is unlikely this figure would be
more than about 20% of the MBL. There would therefore be 20% of the breaking load
remaining before approaching the 100% figure. The brake would therefore still render
before the rope broke.

However, should the brake setting be too high, say 80% of MBL, in the early part of
service it is possible that a rope would approach 100% of its MBL before the brake
rendered. This situation is unacceptable and great care should be taken to ensure the
brake setting is no more than 60% MBL when installing new HMPE ropes on a winch.

4.4 Case studies

Case study 1: Killed by bad practice
A passenger ferry was preparing to leave her usual berth for a scheduled sailing. Wind
and tidal conditions were slight.

In the process of letting go the stern line, the winch operator heaved in the line instead
of paying out slack. The stern line parted and snapped back, striking the officer in
charge on his legs. Both legs were broken and the left leg was almost severed.

The officer’s injuries were severe and it was difficult to control the bleeding. He was
soon evacuated to hospital, where his left leg had to be amputated. He remained in a
critical condition and died 6 days later.

The second officer, in charge of the after mooring deck, was obliged to stand in ‘snap­
back’ zones near the fairleads, so that he could relay orders to line handlers ashore and
deck crew. Analysis of the mooring line after the accident showed that its breaking load
had reduced by almost half, largely due to deterioration from sunlight. Although the
vessel’s mooring ropes were required to be inspected, the on board procedures were
informal and no records were kept.
Case study 2: A damaged line costs a man his leg
The morning after Christmas Day the young port services officer at Freemantle Port in
Australia returned to duty after two days leave. While helping to supervise the mooring
of a liner trade vessel which plied between Asia and Australia, the eye of a mooring line
gave way while the vessel’s crew was applying tension to one of its stern lines. In less
than a fraction of a second, the remnant of the line attached to the bollard on the quay
whipped across to where the officer was standing and sliced almost right through his
right leg just below the knee, leaving it hanging on by a few scraps of sinew and skin.
Although immediately rushed to hospital, the young man’s leg had to be amputated.
Later investigation revealed that the line had been previously damaged, but that no one
had thought to splice out the damaged section or to replace the line.

Case study 3: The officer said: ‘Two ropes will be enough’, but one parted and sliced off
his head
While mooring at a temporary berth before moving next day into its designated berth for
taking on cargo, the officer in charge of the ore carrier’s deck party gave the order to use
just two mooring lines to secure the vessel to its position, believing that as it was light in
the water without its cargo of aggregates, and with good weather and sea conditions,
then just the two lines would be sufficient.

However, he had failed to take into account two factors: firstly, that the tide was on the
turn, and quickly brought about a fast current; secondly, and more dangerously, nobody
had noticed that one of 8­strand conventional synthetic fibre mooring lines being used
had been reduced through abrasion by nearly one third of its diameter along a half­
metre of its length. This line should have been replaced if the damage had been spotted.

The effect of the current on the damaged line was to cause it to part without any warning,
giving the whiplashing length attached to the ship such speed and force that it struck the
officer, who was unfortunately standing in the line’s snapback zone, and sliced off part of
his head, killing him instantly.

Case study 4: Nobody noticed the lines had become too tense
A container ship was unloading in an Alaskan port which is known to have a large rise
and fall of tide. The ship was suddenly hit by squalls which, despite it having run out
extra mooring lines, blew the vessel off the quay. The deck officer went forward with
some crew to adjust the lines. While he was standing on the mooring deck one of the
lines parted and whiplashed back, and before he could move out of the way it struck him
in the head causing severe injuries. Nobody had previously noticed any warning signs
that some of the mooring lines had been put under extreme tension when the squall
shifted the vessel. If they had realised the lines were so taut as to be dangerous then
they should not have gone out on to the mooring deck until the bow thruster had been
started and was able to take some of the weight off the ropes.

Case study 5: The chief put his foot in it – and almost lost it
The crew of a tanker preparing to sail had been sent to stations and the vessel was
singled up while awaiting customs clearance. The last two lines on the foredeck were
those permanently stored on the windlass drums.
Customs clearance was received and the order given to let go forward. When the
foredeck crew tried to slack down the line on the starboard drum for letting go it would
not do so. No one had realised that the berth had been exposed to a heavy swell which
had caused the vessel to surge continually whilst alongside. The surging action had
resulted in the mooring rope on the starboard windlass drum becoming buried in itself
and so when someone went to slacken down the line it jammed.

The chief officer attempted to pull the line clear. To do so he put his foot on the winch­
bearing A­frame support located forward of the starboard drum. The A­frame support
was close to the drum face, which had four flat bar stiffeners welded to it. The stiffeners
passed close to the support, creating a guillotine­like effect. When the drum suddenly
began to rotate the officer’s foot was caught in the machinery through the gap, and
despite wearing steel­capped safety boots he suffered severe injury to his toes.
Fortunately, he was immediately rushed to a hospital where extensive microsurgery
managed to save his foot.

The ship’s winch drums were modified soon afterwards to prevent such an accident
happening again. Nevertheless, this shows the dangers of working too close to winches.
The accident would have been avoided if the chief officer had used some other way of
freeing the rope, which did not involve getting so close to the winch’s machinery. One
possible way might have been to put a stopper on the mooring rope while continuing to
veer, so using the power of the winch to free the rope, but without it being necessary for
anyone to be too close to it.

Case study 6: Not securing the winch cost him his hand
While doing routine servicing of a hydraulic winch, an engineer was injecting a de­
greasing solution at 90 bar. Although he had switched the winch off at the controls, he
had failed, however, to disconnect the power supply completely. During the work on the
internal mechanics of the winch he inadvertently nudged the ‘on’ circuit, setting the
gears in motion. His hand was crushed, and later had to be amputated.

The instruction manual for the winch would have specified that it should have been
completely disconnected from the power source before any work was undertaken on its
interior mechanical assembly.

Case study 7: A risk analysis can save a lot of later grief

A tanker was approaching an oil jetty, one which had been specifically designed for
small vessels, typical of many such jetties in South East Asia. The berth consisted of a
central section containing the loading arms, on either side of which was a mooring
dolphin connected to the berth by walkways.

The tanker manoeuvred alongside the berth in a light condition and without tug
assistance. Its forward draft was only 0.6 metres, and the wind was blowing onto the
berth as the Master made his approach into the current. As he stopped his vessel
parallel to the berth, the high windage forward caused the bows to fall off. The bow of
the vessel entered the space between the dolphin and the berth, coming to rest with the
bow in contact with the central section. To extricate himself the Master put his engines
astern and, in doing so, the fo’c’s’le railing caught one of the chicksands and severely
damaged it.

This incident could have been avoided if a proper risk analysis of the mooring had been
made in advance. Had this been done then a decision might have been taken to ballast
the forward end of the tanker to reduce the windage and increase the grip of the forefoot
in the water, or if operational considerations made this impracticable, then the
assistance of a tug might have been considered. Repairs to the loading arm cost
US$100,000. In a similar incident another vessel demolished four chicksands, causing
US$2million worth of damage.

Case study 8: Never assume anything during mooring operations

A 9,000 tonne vessel was manoeuvring alongside a berth under pilotage, but without tug
assistance. The intended berth was between another vessel and a floating pontoon.
Two head ropes were run ashore by the forward mooring boat. The Pilot then called in
the stern mooring boat to run the after back spring, since the tide was from ahead.
However, before this could be done, the vessel started to be set astern and the Pilot
instructed the stern mooring boat to keep clear because he was about to use the main
engines.

The vessel was manoeuvred ahead and the Pilot again called in the stern mooring boat.
However, there was some difficulty in securing the two head ropes ashore, and the
vessel started to drift astern again. Although the Pilot could not see the stern mooring
boat he assumed it was clear of his propellers and began to use the main engines again
to manoeuvre the vessel ahead.

The wash from the propellers caused the stern mooring boat to capsize, throwing its two
crewmen into the water. Fortunately, both men were wearing self­inflating life jackets
and managed to climb uninjured onto the floating pontoon.

This event demonstrates the need for good communications between all those involved
in mooring operations, and for always getting confirmation that something that should
have been done has indeed been done, such as that mooring boats are clear of the
propellers before the main engines are used. The accident also demonstrates the need
for everyone engaged in mooring operations to always wear an inflatable life jacket.

With hindsight, it is probable in this case that if a single head rope could have been
secured quickly it would have enabled the vessel to be held against the tide without any
further need of the main engines.

Case study 9: Watch that line!

A small harbour tug was acting as stern tug to a 92,000 tonne vessel which was berthing
in good weather and tidal conditions. In repositioning herself and passing across the
stern of the larger ship when the ship's engines were running ahead, the towline came
under very heavy load and quickly reached an angle of 90º to the fore and aft lines,
causing the tug to capsize within seconds. Both crew members on the tug drowned.
Case study 10: When patching up can kill
A small tug was towing a barge at the approaches to a pier off the west coast of Ireland.
The crew of the tug had used an old car tyre to join two lengths of rope to form a longer
tow line. During the tow the tug accelerated, causing the tow line to part where it was
tied to the tyre. The part of the line still attached to the tyre whiplashed back towards the
barge, where it struck and killed a crewman standing at its bow.

Case study 11: Out of sight, out of mind – then dead

While assisting with the berthing of a tanker, a tug’s tow rope was led from its towing
hook to the centreline at the stern of the tanker. A bridle wire was led from a winch
through a swivel block, located at the stern of the tug, to a saddle attachment positioned
around the tow rope.

The mooring manoeuvres reached a stage when the use of the bridle arrangement was
no longer needed, and two of the tug’s crew left the wheelhouse to get ready to retrieve
the bridle wire. One of them went to the after working deck and stood between the leads
of the tow rope and the bridle wire. When the bridle wire was slackened, done from a
control position in the wheelhouse, the slackening caused the saddle attachment to slide
very quickly down the tow rope which, in turn, caused the bridle wire to hit the crewman,
killing him instantly.

This event demonstrates the importance of making sure that all those engaged in
mooring operations should be clearly visible to whoever is in charge, or that they are in
communication with the supervisor. In this case, the dead man had been in a position on
the after working deck which was out of sight of both the Tug Master and the bridle wire
winch operator at their control positions in the wheelhouse.

Case study 12: Only six minutes from disaster

A 10,000 tonne cargo vessel was being towed upriver at 5 knots and at night, to its
discharge berth by two tugs when they came into an unexpected fog bank. The river
was narrow and the bow and stern towlines were each only 30 metres long. In the fog
the vessel’s Master and the skippers of both tugs all became disorientated by lights on
the river bank on each side. During the confusion, to avoid hitting each other and with
the danger of running aground or the towlines girting the tugs, all three vessels each
took their own independent actions. However, within six minutes all three vessels had
collided with each other.

At the later inquiry the reasons for the disaster were found to be complex, but at the
heart of the accident was found to be a fundamental failure of communications between
all three skippers and the Pilot on board the towed vessel, as well as a very
praiseworthy reluctance by the two tug skippers to immediately slip their towlines at the
first hint of trouble, because they wanted to try to save their tow from grounding.

An important lesson learned from this event was that during towing operations good
communications between everyone involved is vital – especially in case weather and
visibility conditions worsen.