Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
1
Towing Techniques
Contents Overview .................................................................................... 2
1. Coastguard Policy ................................................................... 2
2. Towing Configurations ........................................................... 2
2.1 Straight Tow ........................................................................ 2
2.2 Fixed Bridle or ‘Y’ Tow ........................................................ 2
2.3 Adjustable Bridle ................................................................. 3
3. Line Handling .......................................................................... 3
3.1 Hazards ............................................................................... 3
3.2 Chafe Gear .......................................................................... 4
4 Messenger Lines ...................................................................... 4
5. Catenary Devices .................................................................... 5
6. Drogues .................................................................................. 5
7. Kicker Hook ............................................................................ 5
8. Towing Equipment Maintenance .......................................... 6
9 Forces in Towing ..................................................................... 7
9.1 Yawing ................................................................................. 7
9.2 Burying the Bow .................................................................. 7
9.3 Stopping and Swamping ..................................................... 8
9.4 Being Overtaken by the Tow .............................................. 8
9.5 Towing Speed ...................................................................... 9
10. Towing Situations ................................................................ 9
10.1 Sinking Tow ....................................................................... 9
10.2 Vessel Aground ................................................................. 9
10.3 Heeling a Vessel Aground ............................................... 10
10.4 Vessel at Anchor ............................................................. 11
10.5 Towing Alongside or Barging .......................................... 11
10.6 Berthing a Tow ................................................................ 12
11. Summary of Standard Towing Practice ............................. 12
Towing is
potentially
hazardous to both
vessels and all
crew involved,
therefore
knowledge of safe
towing procedures
is paramount for
all CRV crew.
Constructive
feedback and
suggestions for
improvements to
the SAR Training
Matrix is
appreciated. Please
email feedback /
suggestions to
sartrainingfeedback
@coastguard.co.nz
providing as much
detail as possible.
Thank you.
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
2
Overview
Towing is potentially hazardous to both vessels and all crew involved, therefore knowledge of safe towing procedures is paramount for all CRV crew.
1. Coastguard Policy
The primary responsibility of Coastguard during a SAR operation is the
preservation of life. The Skipper of the CRV must consider the possible
danger to people on board the disabled vessel and decide whether to
tow the disabled vessel and its crew, or to transfer those people to the
CRV.
A tow operation to remove a vessel and crew from danger is only strictly
a SAR operation until reaching the nearest safe haven. To continue the
tow beyond this point must be within the Unit SOP, regional policy, and
agreed by the skippers of both vessels.
2. Towing Configurations
The most common arrangements for towing fixtures on the CRV are:
2.1 Straight Tow The towline is made fast to a single fitting (bollard), often positioned on
the centreline some way forward of the vessel’s transom. This
arrangement allows the stern to swing while towing. This will give
greater control and manoeuvrability than if the towline is attached
directly to the stern.
2.2 Fixed Bridle or ‘Y’ Tow The bridle is made fast to the CRV quarter cleats. The towline is attached
to the apex of the bridle. The main towline is a set length and any
adjustments to the towline length are made using the bridle line. A
disadvantage of this method is that to lengthen the towline by 5m you
may end up paying out almost 10m of bridle line. The advantage is that
Maritime
Regulations
Maritime Rule 22
’Collision
Prevention’ provides
the steering and
sailing rules for
towing, while the
standards for
installation,
performance and
use of lights and
sound signals are
covered by Rule
22.24 ‘Towing and
Pushing’.
“One safety rule
that must be
followed when
making up the
bridles is that the
length of each leg
of the bridle must
be at least one and
one half times the
width of the tow.
For a barge with a
beam of 50 feet,
each bridle leg
would be at least
75 feet long.”
FM55-501Marine
Crewman’s
Handbook (1999)
Dept. of the Army,
Washington.
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
3
the strain of the tow will be equally divided between the two quarter
cleats.
2.3 Adjustable Bridle An adjustable bridle which allows the towline length to vary is more
desirable but has the complexity of dealing with blocks and extra line.
The bridle can be made up of a block permanently attached on the end
of the main towline with the bridle line being lead through the block.
Another method for an adjustable bridle is to pass the main towline
lead through the block where it is tied off to one of the quarter cleats.
The other line from the block is tied to the other quarter cleat – this
block line can be adjusted to ensure the tow line is centred.
By using this method the amount of line needed on board the CRV for
towline adjustment is reduced, but the strain imposed by the tow will
not be equally divided between the two quarter cleats because the
majority of the strain will be on the cleat taking the main towline.
3. Line Handling
3.1 Hazards Whatever method is used for towing, care must be
exercised when attaching the towline to the CRV so that
the towline’s lead is ‘fair’. This will reduce the chance of
the towline trapping itself on the cleat or post.
All CRV crew should be aware of the potential hazard of the towline
parting and its subsequent recoil. Great care must be taken to ensure
the towline is stowed correctly and is free to run at all times.
Avoid putting yourself in a position where a parting line and
subsequent recoil will put you at risk.
Do not handle lines under load close up to the fitting; always
keep a safe distance between the fitting and your fingers.
“The Towline can
be a deadly killer
and many forget
how quickly things
can go wrong when
a line is under load.
The crew must
ensure all gear
(lines, shackles,
messenger,
drogues, tow bits,
chafing gear,
fairleads, etc.) have
been checked for
wear and tear.”
Canadian Coast Guard
Auxiliary Search &
Rescue Crew Manual
Activity:
Towline safety
Towing can be deadly
and it is vital all gear is
checked and crew
operate safe practices.
• Divide a whiteboard
into two columns.
Label one ‘Towing
Gear’ and the other
‘Line Handling’
• Ask the crew to think
about all those safety
aspects that should
be considered as they
prepare for a tow.
• Some examples for
‘Towing gear’ are
towline is attached to
designated strong
point on CRV and
towed vessel, use
your own towline if
possible, towline
should be clean and
free from debris, no
chafing, towing eye
used where possible
rather than knots
• Some examples for
‘Line Handling’
include never use
hitches to secure a
towline, avoid
adjusting length of
tow while underway,
always stay out of the
bight (turn) especially
around tow post,
never handle lines
close to fittings etc.
• Once the lists are
generated discuss
crew responsibilities
and how safety can
be managed.
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
4
If gloves are to be worn, they should only be close fitting finger-
less type gloves which will not become trapped by a line.
3.2 Chafe Gear Any towline in use can be subject to high loading and consequently
suffer damage from chafe on the towed vessel’s fairleads or stem fitting.
One of the most cost effective and robust types of chafe gear is simple
flexible plastic hosing. The hosing can be already on the towline when it
is passed and subsequently held in position with a simple clove hitch or
preferably a rolling hitch (or any form of lashing that keeps it in place).
If hosing or similar is not available, any suitable chafe gear should be
considered such as old towels or clothing. It can take only a few minutes
to seriously damage a line exposed to chafe.
4 Messenger Lines
A messenger line is simply a length of light line attached to the towline
that can be thrown, propelled or floated to a vessel or person.
A heaving line is a light line with a ‘monkey’s fist’, sand pouch, or similar
weight at the throwing end. The other end of the heaving line is secured
to the towline. Securing the heaving line approximately one metre from
the towline eye will enable the eye to be placed directly onto the bollard
post or cleat on the disabled vessel without trapping the heaving line.
A standard ‘throw bag’ can be used as a messenger line. They are made
from polypropylene and can be thrown or used to float a line to the
disabled vessel.
A floating line (polypropylene), used
with a life ring, fender or lifejacket,
may be floated from upstream /
upwind, so that the current or wind
carries the line to the disabled vessel.
This can be slow and difficult to
achieve so is usually only attempted
in exceptional circumstances.
A rocket line thrower or shoulder
line-firing gun may be used to pass a
towline when conditions are such
that your vessel cannot get close
enough to the disabled craft to use a
heaving line. They are predominantly
used when forced to throw into
strong wind. Similar to a heaving line
aim high to allow the line to land
over the deck. Never aim directly at
the other vessel or its crew.
Preparing two
heaving lines is
recommended. If
the first pass is
unsuccessful then
the second line can
be tossed
immediately.
It is shock loading
that is the greatest
cause of towlines
parting or pulling
out fittings.
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
5
5. Catenary Devices
A catenary is the curve or dip in a line caused either by the weight of the
line or by a weight attached to the line. If a towline is stretched taut
between two vessels any shock loading is transmitted directly through to
both vessels.
Having a catenary in the line means that part of any dynamic loading is
absorbed by having to first lift and stretch out the towline - the longer
the towline the more catenary
The space available on board many CRVs means that the length of
towline alone may not be enough to induce the desired catenary, so
additional weight may need to be added to the towline.
6. Drogues
A drogue slows a vessel down and produces greater directional
stability.
Drogues come in various designs and should be of a size
suitable for the vessel.
There are adjustable drogues that can be used for a range of
different sized vessels.
Deployed from the towed vessel’s stern a drogue will help to
prevent it surfing down the face of a wave or sheering from side
to side.
Drogues are useful when a towline has been shortened up in preparation
to enter harbour, when running a bar, or when towing in a following sea.
If a suitable patented drogue is not available, other equipment may be
used in its place but it needs to be robust enough to withstand the forces
involved. Warps streamed in a single line or in a bight, with objects
attached such as water containers and fenders (weighted down) have all
been used as drogues.
7. Kicker Hook
It is a device which can be used to fasten a towline to the ‘trailer eye’ (an
eyebolt on the waterline under the bow) of a trailer boat (a difficult and
potentially dangerous operation at sea).
“You must
familiarise yourself
with the operating
characteristics and
effectiveness of
drogues under
differing conditions.
The time to learn
about a drogue is
before you need to
deploy one.”
Section 10.4.8 from
SAR Seamanship
Reference Manual
(2001). Canadian
Coastguard.
It is shock loading
that is the greatest
cause of towlines
parting or pulling
out fittings.
“You must
familiarise yourself
with the operating
characteristics and
effectiveness of
drogues under
differing conditions.
The time to learn
about a drogue is
before you need to
deploy one.”
Section 10.4.8 from
SAR Seamanship
Reference Manual
(2001). Canadian
Coastguard.
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
6
Many trailer boats do not have deck fittings of sufficient size or strength
to rely on for towing, with the exception of the trailer eye, and towing
from the trailer eye is the preferred method as it helps to lift the bow of
the towed vessel.
Any towline attached to the bow of a vessel will depress or pull down the
bow (referred to as a vessel trimmed by the head / bow). The smaller the
vessel the more pronounced this effect can be. Any vessel trimmed by
the head will be harder to control and will have a greater tendency to
yaw (swerve from side to side). When possible trailer boats should be
towed from the “trailer eye” to prevent this from occurring.
8. Towing Equipment Maintenance
All equipment used in towing should be checked regularly.
Any damaged or worn equipment should be replaced at the first
opportunity.
Any rope used should be from a reputable manufacturer or
supplier and have known ratings for strength and stretch.
Any hardware used such as shackles should be from a reputable
manufacturer or supplier and have known ratings for strength.
Any hardware used should be inspected regularly for signs of
corrosion or fractures.
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
7
9 Forces in Towing
Most accidents that do occur during towing operations can
be traced back to insufficient preparation, inappropriate set
up, or inadequate monitoring of equipment and crew during
the tow. To appreciate the inherent dangers in towing an understanding
of the forces acting upon both the towed and towing vessels is essential.
9.1 Yawing Yawing is when the towed vessel swerves off course, and can endanger
both the towed vessel and CRV. To prevent or reduce a towed vessel
yawing:
make sure the tow line is pulling the towed vessel from a point
on its centreline.
decrease speed.
lengthen the towline.
ensure that both CRV and towed vessel are in step with each
other (on the same part of a different wave).
if possible trim the towed vessel down by the stern. Lower
outboards for example on smaller vessels, or move weight(s) to
the stern.
whenever possible tow trailer boats from the towing eye.
deploy a drogue or similar from the stern of the towed vessel.
engine on towed vessel centered and if necessary lash the tiller.
9.2 Burying the Bow The CRV can cause the towed vessel to bury its bow by getting the tow
out of step with the wave pattern, or by towing at too high a speed.
This is common in steep waves and can happen while travelling at any
angle into or before the sea. In a head sea burying the bow of the towed
vessel can create huge loadings on the tow line and risk swamping the
towed vessel. In a following sea there is the danger of the towed vessel
broaching. If possible always attach the towline to the towing eye of
Forces involved
include:
Static forces: those
forces that cause a
vessel to resist
motion. Bigger
vessels require
greater force to get
it moving.
Momentum: once
the vessel starts
moving it will
continue in same
direction. The
bigger it is or faster
it moves = harder
to stop or change
direction.
Friction resistance:
this is the water
drag on hull. The
faster speed =
more power to
keep it moving.
Form drag: this is
the effect of the
hull shape on the
ability to move the
vessel (changing
course and
maintaining
heading)
Activity:
Being Aware
Crew have a
responsibility to
maintain watch and
notify the Skipper if
they see anything of
concern.
Give the crew the
following list of issues
and ask them what
each may indicate and
what the response of
the crew / skipper
could be.
Anyone on board the
tow indicating
distress
Tow moving from
astern to one side
Towed vessel veering
back and forth
Towline stretching
and pulling
Towline unravelling
or fraying
Towline groaning or
overloaded
Towed vessel settling
in the water or
sinking
Securing points
moving or coming
loose
Bow of towed vessel
being swamped
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
8
trailer boats to help lift the bow. Towing above the planing speeds
induces this problem much more readily than tows carried out at
displacement speeds.
9.3 Stopping and Swamping The towed vessel can cause the CRV to both stop and then to be
swamped by following seas if it has got out of step with the sea state
when being towed in a quartering or following sea. The towed vessel
falls behind one wave while the CRV is in front of the same, or another
wave. If the towed vessel buries its bow, its reserve buoyancy is enough
to dramatically slow down or stop its progress through the water. This in
turn affects the CRV which can be overrun by waves as its stern is held
down by the weight of the tow.
9.4 Being Overtaken by the Tow This occurs when the CRV and the towed vessel get out of step. The CRV
either slows down or stops, or the towed vessel accelerates down or
across a wave (with the possibility of broaching) and overtakes or
collides with the CRV. The same thing can happen if the CRV slows down
too quickly, and does not allow for a natural rate of deceleration for the
towed vessel. The heavier the vessel, and higher the initial speed, the
more momentum it will have.
All of the above hazards are likely to occur if the CRV and casualty are
out of step with one another, and they will all increase the risk of the
towline parting or pulling out fittings.
The general rule for
towing astern in
open water is to
use as long a tow
line as possible, and
always ensure the
vessels are in step
with each other.
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
9
9.5 Towing Speed Displacement vessels should never be towed at or above their hull speed
because:
Fuel consumption rises considerably for the CRV.
Enormous strain is put on the towline and fittings as the towline
tries to literally drag the vessel up and through its own bow
wave.
The risk of pulling out a fitting or snapping the towline
increases.
Small vessels can be swamped and sunk while under tow purely
because they were towed at excessive speed.
Any loss of support to the towed vessel while planing, such as
wave effects, turning, change in weight distribution or change in
speed may well cause a rapid drop off the plane and a potential
hazard from the effects of rapid deceleration and / or yawing.
10. Towing Situations
10.1 Sinking Tow If time allows the vessel should be towed out of any shipping channels
and possibly beached. In shallow water and if safety permits pay out the
towline and buoy off its end so that it is visible on the surface. Note the
sunken vessels position and report the situation. Have a method of
cutting the tow line ready.
10.2 Vessel Aground For a vessel that has run aground on a falling tide, often by the time a
CRV arrives on scene, towing the vessel off is no longer possible. The
best that can be done is to secure its position and await the next flood
tide.
Approx Max towing
speed = Sq root of
waterline length in
feet x 1.34.
Safe towing speed
= 90% of approx
Max towing speed.
All towing
operations should
be carried out at
speeds suitable for
the conditions.
Any vessel that
sinks becomes the
responsibility of the
Local / Regional
Harbour Master or
MNZ depending on
its location. Units
must be aware of
their local
procedures &
protocols in regards
to sunken vessels.
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
10
For a vessel aground on an incoming tide, all that may be needed is to
secure the vessel in position and wait for the tide to do the rest.
Before assisting a vessel aground, the CRV crew must make a thorough
analysis of the situation. Consider;
Are crew uninjured and accounted for?
Advise vessel’s crew to put on life jackets
Is the vessel damaged in any way, or taking on water?
Is the vessel leaking any fuel /oil?
What is the vessel’s draught?
No immediate attempt should be made to pull off a vessel that has been
or is suspected to have been seriously damaged or if there is any doubt
as to the vessel's ability to remain afloat.
If the CRV assessment reveals that the vessel will remain afloat, carefully
determine the refloating procedures to use. When preparing to tow free
a grounded vessel the Skipper and crew of the CRV must always assess
the possible hazards to their own vessel. There are too many cases of
one vessel attempting to help another, then subsequently running
aground or suffering damage to their own vessel in the process.
10.3 Heeling a Vessel Aground For any vessel with a deep keel, heeling it over to one side will effectively
reduce the draught. This is a method most commonly employed with
yachts. Lead a halyard from the mast to another vessel or a fixed object.
Care should be taken that the halyard used will not foul and put undue
strain on the yacht’s rig when it is heeled. The spreaders or crosstrees on
a yacht rig are designed to take compression loading from the standing
rigging. They are not designed to take large loads in a fore and aft
direction.
Before attempting
to tow off a
grounded vessel,
the skipper of the
CRV must answer
the question - is it
necessary?
Coastguard’s
primary role is
saving lives not
property.
Refloating the
casualty will
probably not be
considered a
success if you
dismast it in the
process!
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
11
10.4 Vessel at Anchor A disabled vessel will often have put down its anchor. If there is
sufficient sea room the anchor can be raised and the vessel allowed to
drift before setting up the towline. This at least allows a clear foredeck
prior to accepting the tow. If the vessel is close to a lee shore then the
towline may need to be attached prior to raising the anchor.
A problem can occur when a vessel is unable to raise its anchor. The
anchor may need to be ‘tripped ‘by the CRV. If the anchor cannot be
tripped, or the CRV Skipper decides that tripping the anchor is
unnecessarily hazardous, then it will need to be left behind. If the anchor
is left behind then a GPS position should be taken and the end of the
anchor rode buoyed so that it can be retrieved at a later date.
10.5 Towing Alongside or Barging There are 3 common ways in which a tow astern can be transferred to an
alongside tow:
• While Underway
• While at Anchor
• While on a Mooring
Towing alongside should only be attempted in calm to slight seas, and
for a short period of time. To give the greatest amount of control over
the tow the CRV should be tied alongside the vessel as far aft as possible
while still remaining secure alongside. With vessels smaller than the CRV
the positioning generally isn’t that critical, however with vessels the
same size or larger it becomes increasingly important.
• The CRV should be made fast using a bow line, stern line, and
spring lines to prevent the vessels surging.
• All lines should be positioned so that adjustments can be made
on board the CRV.
A bight of line or
preferably a short
length of chain is
passed around the
anchor rode and
pulled slowly and
gently along the
rode until it comes
in contact with the
anchor. The anchor
is then pulled out
by the CRV.
Securing the CRV
so that its bow is
pointed in slightly
ensures that when
moving ahead the
water pressure
created is keeping
the vessels
together, not trying
to force them
apart.
Towing Techniques – Version 1 (2013) ©Coastguard New Zealand 2014
12
• Once secured alongside all slack in the lines should be taken up,
with the bow of the CRV pointing in towards the other vessel by
about 10-15°.
• There are no hard and fast rules as to exactly how the tow is
made fast, each vessel will be different as the position of the
cleats or posts available will determine how the tow is finally
secured.
10.6 Berthing a Tow Before committing to any close quarter manoeuvres it is imperative to
test manoeuvrability. Performing a figure of eight then coming to a stop
will give you an indication of your turning circle and stopping distance.
Sometimes even a ‘safe berth’ can present difficulties if there is a strong
wind or tide. CRVs usually have more than adequate power
and manoeuvrability to berth in adverse conditions, but that
may not be the case with another vessel tied alongside.
11. Summary of Standard Towing Practice
Standard practice that should be adopted when towing;
• Operate with an extended tow line in open water, generally the
longer the better.
• Always try to keep the towed vessel and CRV ‘in step’.
• As necessary deploy a drogue from the towed vessel to reduce
its potential to yaw.
• Trim the towed vessel down by the stern if possible.
• As necessary employ a catenary device in the tow line to
minimise snatch loading.
• Tow at a safe speed – For a displacement vessel with
consideration for its max hull speed, and for all vessels at all
times a speed suitable for the conditions.
When planning to
berth a tow it
should always be
remembered that
the CRV is obliged
to secure the towed
vessel to a safe
berth not
necessarily its
customary berth.
Activity:
Towing SAP.
The SAP process is vital
in preparing for a tow
(see CRM Module).
Gathering information
to assist in the planning
phase is vital (assessing)
– but what information
should be collected?
Visual assessment
• Have the crew work
in small groups. Give
each group one
aspect of visual
assessment (from
vessel state, people
on board and
environmental
factors) and have
them write a list of
dangers and other
factors that should be
considered as they
plan for the tow.