Anchoring a Ship

Anchoring is as frequent operation on board as loading and

unloading a cargo.
But in spite of being a frequent operation, the number of
incidents related to anchoring never seem to reduce.
That is when many minor incidents never come to light to a
wider audience.
The truth is that even after being a routine operation,
effective way of anchoring is not a child’s play.
Sure one can just somehow arrive at anchoring position and
open the brake to anchor a ship. I am sure you would agree
that it is not an effective way of anchoring. Don’t you think
so?
So let us discuss a practical way of anchoring.
But before we do that, we need to discuss two things. First
how an anchor holds the ship. And second what guarantees
more holding power of anchor.
1. How an anchor holds the ship
When an anchor is dropped, The crown of the anchor is the
first to hit the sea bottom. As the ship moves back, the flukes
take its position and embed itself into the seabed.
It does not matter from what height the anchor is dropped,
the crown will always hit the bottom first. The flukes will only
dig into the seabed once the ship moves aft and flukes are
facing downwards into the sea bottom.
As the ship moves back, the fluke takes its position and
embed itself into the seabed.
The opposite happens when we pick up the anchor. When the
chain is all picked up, the flukes face upwards and gets
uprooted from the bottom.
2. Holding Power of anchors
All other factors being common, there are three things that
affect holding power of anchors. First is the construction of
anchor, second nature of seabed and third the scope of the
cable.
Holding power due to anchor construction
A ship’s Equipment number decides the weight of the anchor
and length of the chain.
The fluke area determines the holding power of the
anchor. International Association of Classification Societies
(IACS) governs the rules for anchors.
IACS enlist three types of anchors.
Normal holding power anchors,
high holding power anchors
Super high holding power anchors.
Because of the high and super high holding powers, these anchors can
have a lesser weight than the normal anchors. This is because the high
holding design (Larger fluke area) compensate for the loss of holding
power due to lesser weight.
Even though anchor weight has nothing to do with holding
power per se, it contributes to some extent in holding a ship
in its position.
More weight of the anchor would need more force to push
the ship from its position. For this reason, anchor weight is
more often used as a function of holding power.
Holding power due to nature of Seabed
Another factor that affects the holding power of the anchors
is nature of seabed.
Sand is considered to be the strongest holding ground. Soft
mud is the least holding ground. This is because of obvious
reasons.
Anchor embedded into soft mud would leave the bottom
easily compared to the more harder surface like
sand. Mariners must consider nature of seabed to determine
the possibility of dragging of the anchor.
Holding power due to scope of the anchor cable
The correct scope is essential for safe anchoring and better
holding of the anchor. The scope is the ratio of the depth of
the water to the length of the cable deployed.
More the scope, better an anchor will hold the ship. The idea
of having more scope is that the angle of chain with respect
to sea bottom should be minimum. More the angle, lesser the
holding power. OCIMF (Oil Companies International Marine
Forum) has published a graphical relation between this angle
and holding power of anchor.
As a thumb rule, Scope of 6 is advisable for anchoring. That is
when anchoring into a depth of 20 meters, we should pay at
least 120 meters of cable. When anchoring in areas of strong
wind or current, we should have a scope of more than 6, up
to 10 sometimes.
There are two situations where the scope of 6 or more may
not be always possible.
In congested anchorages like in Singapore and in deep water
anchorages like Fujairah.
In congested anchorages, this is due to insufficient sea room
and in deep water anchorage due to insufficient cable length.
In calm weather, the lesser scope in these areas should not be
a problem.
But if you expect wind force to increase, increased possibility
of anchor dragging should be part of the risk assessment.
Anchoring a ship.
3. Preparing for Anchoring
Preparing the vessel for anchoring can start days before
arrival. This is when a Master checks the charts for marked
anchorage areas days before arrival.
Anchorage area for the vessel could also be suggested in the
agent’s pre-arrival message. In any case, the Anchorage area
must be physically checked in the chart to ensure that
it is designated for the type of ship, the depths complies with
the UKC requirement of the company depths are less than the
maximum depth ship can anchor is clear of any cables,
pipeline, wrecks or other obstructions and the nature of
seabed is appropriate for anchoring When checking the
charts for underwater obstructions, attention should be paid
to the chart symbol ‘#’.
This symbol means there is a foul ground and shall be avoided
for anchoring. Particular mention is required for this chart
symbol because you may not miss a wreck but it is easier to
miss this.
It is important to be aware of the ship’s windlass lifting
capacity. In any case, most of the ship’s windlass are able to
lift the weight of the anchor and about 3 shackles.

Vessels could easily anchor in depths of about 80 meters. If

anchoring in depths more than that, you might need to first
check the windlass capacity for the particular ship.
4. Anchor stations
Anchor stations should be ready forward well in advance. The
anchor party should make the inspection of the anchor
windlass.
They should also ensure that the drive (Hydraulic power packs
or electric power) is running. The lashing of both the anchors
should be removed even if it is pre-decided about which
anchor will be used.
It is a good practice to brief anchor party well in advance of
some information about anchoring such as

❑the depth of water at the anchoring position

❑Which anchor to use
❑Anchoring method (Let go or walk back)
❑the number of shackles the vessel will be brought up to.
5. Approaching the anchorage position
The most critical factor while approaching anchoring position
is the speed of the vessel. Engines must be ready and tested
well in advance and the speed of the vessel should be under
control.
If Master feels the ship’s speed is much more than what it
should be, he should exercise zig-zag manoeuvre to reduce
the speed.
Zig-zag manoeuvre (also called rudder cycling) is the most
effective way to reduce the ship’s speed over a shorter
distance.
While doing rudder cycling, the master must give due
consideration to the nearby ships and not run over other
ships in the vicinity. Apart from speed, the direction from
which to approach the anchoring position is important.
The best approach heading is of heading into the wind and
tide. The heading of similar sized anchored vessels can give a
quite accurate sense of the approach heading. If the traffic
density, water If the traffic density, water depth, and sea
room permits, it is better to bring the vessel to this heading at
least 1 mile from the anchoring position.
Once on this heading, engine movements should ensure that
vessel’s speed is less than 2 knots about half a mile from the
anchoring position.
These are just referencing but useful figures. You should
consider vessel’s maneuvering characteristics, such as
stopping distances to amend these figures. Once the vessel is
around half a mile from the anchoring position, we can give
stern movement. This is to ensure that vessel is completely
stopped at the anchoring position and there is no headway in
the forward direction.
During Stern movement, the vessel would cant to starboard
side (for right hand fixed pitch propellers).
If we are using the port anchor, this is good as this would
ensure the cable is clear of the vessel and will not lead across
the bow.
But if starboard anchor is used, there is a chance of anchor
chain going under the bow or crossing the bow. In this case,
before we give stern movement, vessel’s rudder is put to hard
port to get some port swing. The stern movement would
check the port swing and the cable going under the bow can
be avoided. Make sure to bring the rudder to midship during
Stern movement. Apart from lateral swing, stern movement
of the vessel itself ensures that the cable is clear of vessel’s
hull. However, in all cases, we must ensure that movement of
the vessel does not put excessive strain on the windlass. We
will discuss this in the next section.
6. Anchoring Methods
As we know, there are two ways an anchor can be dropped to
the seabed.

By letting go
by walking back.

Each of these ways has its advantages. And in most of the

cases, it is up to the discretion of master how he wants to
anchor.
But there are certain conditions in which there are no options
but to choose a particular method.
Letting go an anchor
Would you agree that anchoring by letting go is easier of the
two methods? It is the most used method of anchoring too.
In this method, we open the windlass brake to let the anchor
go under gravity.
Before opening the brake, we must consider the height from
which we plan to drop the anchor.
If we don’t, we may damage the anchor. Depending upon the
height, the damage may not be visible in the same operation
but will be visible in the longer run.
There is another obvious risk of dropping the anchor from a
height. The anchor under its weight will continue to gain
momentum until it touches bottom. This momentum will
increase
The anchor under its weight will continue to gain momentum
until it touches bottom. More the height, more momentum
the anchor will gain. This momentum may increase to a point
where windlass break would not be able to hold it. The
anchor’s momentum will only stop when the anchor along
with entire chain is in the bottom after it has been uprooted
from the bitter end. What is the referencing height then?
As a thumb rule, you should never allow the anchor to drop
from a height of 20 meters. That is, one must lower anchor
to a level when the distance between the bottom and the
anchor is not more than 20 meters. But that is a maximum
figure. One must lower the anchor to as close to the bottom
as possible before it is let go. But if you aim for lowering the
anchor to say one meter above the seabed, you may end up
touching the anchor to seabed while the ship still has some
speed. That is not good.
So here is another rule of thumb. We should aim for lowering
the anchor to around half shackle from the bottom before we
let go.
To summarize, here is how we should anchor the ship by
letting go
▪Approach the anchor position heading into wind and tide
with speed around 2 knots at 0.5NM from the position.

▪Lower the anchor with gear to around half shackle off the
bottom and then hold the anchor on brake

▪Give Stern movement to stop the vessel over the ground

once the vessel is in the anchoring position. if using starboard
anchor, check the starboard swing (for Right hand fixed pitch
propellers) because of Stern movement.
▪When in position, drop the anchor by opening the brake
maintain around 0.5 knots stern speed to allow the cable not
to pile up.

Hold the break once required cable length is paid out.

Anchoring by walking back

Walking back means lowering the anchor with gear.
The principle difference between walk back and let go
methods is that in the walk back we lower the anchor under
power.
The advantage of this method is that cable would not run on
its own. So there is no risk of damaging the anchor or
windlass by dropping from a height.
But there is another risk involved with this method. I earlier
said that in the “let go” method we should maintain around
0.5 knots astern speed while we are paying the anchor chain.
But even if we exceed this speed to 1.0 knots, only the anchor
will pay off. There will not be any load on the windlass. Even
when the brake is on, and the chain stresses, windlass brake
will be the first thing to render.
But that is not the case with walk back method. In walk back
method, since we are lowering the anchor with windlass in
gear, excessive speed would surely damage the windlass.
We must not exceed the stern speed to more than the design
speed of the windlass. Typically the design speed of windlass
is 9 meters/minute. That is 540 meters/hour (0.3 knots). So
we must not exceed the stern speed to more than 0.3 knots
while walking back the anchor.
7. Anchor brought up
Once we have lowered the required anchor length, and we
have disengaged the gear (in the case of the walk back), we
then wait for the anchor to be brought up.
The anchor is brought up when it leads to the long stay and
then gradually comes back to short to medium stay.
Once brought up, there is an important thing that we need to
do. Put the bar (Bow stopper) on and rest the anchor chain
on it.
This is because the load generated by the vessel’s movement
during its stay at anchor should be borne by the bow stopper
which has higher capacity than the windlass system.
There is a disadvantage though. In heavy weather, there are
chances that stopper may jam or deform. In this case, if for
some reason vessel needs to let go the cable in the
emergency, it would be difficult.
The only solution to it is that the Master must get underway
before putting any component of anchoring at the risk of
damage. Most of the companies have instructions to the
masters to leave the anchorage if wind force is more than
force 6. There have been incidents of total constructive loss
due to master’s decision to stay at Anchorage in spite of
adverse weather warnings.
DEEP WATER ANCHORING
Should it become necessary to anchor the vessel in an
emergency, or in anchorages such as the Norwegian fjords,
the Master may be forced to a deep water anchorage.
Should this occur, the anchor should not be let go in the
normal manner, but walked back all the way to the sea bed.
The anchor party should have an idea of the depth of the
water, and be able to estimate when the anchor is on the
bottom.
As the vessel drops astern once the anchor begins to hold,
the cable should be seen to grow slightly. However, because
of the considerable weight of cable in the vertical up and
down position, it will be increasingly difficult to see the cable
snatching or growing to indicate that the vessel is brought
up. The officer in charge of the anchor party should be aware
of the total length of cable that the vessel is equipped with
to each anchor. Bearing this in mind, a close watch should be
kept on the amount of cable being payed out. Many vessels
have the joining shackle of the last length (shackle) of cable
painted a distinctive colour for this reason.
When lowering away, under no circumstances should the
anchor cable be allowed to run out from the brake. Control
could be lost with the excessive weight of cable in use,
resulting in possible loss of anchor and cable, together with
serious damage and possible injury.
Conclusion
Anchoring is a routine job. Number of incidents during
anchoring or while at anchor suggest that we might not have
yet mastered the art of anchoring a ship effectively.
Knowing the correct anchoring procedures and their
limitations are one of the best ways to avoid anchoring
related fatalities and damages.
DRAGGING ANCHOR
Raise General Alarm, inform master, warn other ships in
the vicinity and, if necessary, seek the help of harbour or
port pilots and tugs.

Establish the cause of the anchor dragging. Call up office

immediately or send an email, depending on the urgency,
detailing the circumstances of the anchor dragging and
action being taken by Master.
If risk of collision or contact with another vessel exists then:

1. Vessel should consider which of the two is the better

option to be taken within the short time available, i.e.
picking-up anchor and moving away or paying out / slipping
the cable to increase the distance / time from contact.

2. If time and circumstances permit, pick-up anchor and

move to a safer location.

3. If time or circumstances do not allow for picking up the

anchor then:
a. Try running out the rest of the chain to increase distance.

b. If this is likely not to or will not avoid contact with other

vessel then cable may be slipped from the bitter end (with
anchor buoy which was rigged on arrival) and the vessel
manoeuvred out of the danger.

4. If time or circumstances do not allow for slipping of the

anchor then use engines boldly to dredge the anchor, in
which case the crew should be in a safe area well clear of the
windlass and anchor chain. In the worst case scenario an
astern movement (full) on the engines will only result in the
cable snapping at the stopper and being lost with the anchor.
5. In an emergency, if collision is imminent, it is preferable
to lose the anchor than to have contact with another vessel.

In many cases it has been observed that even when

collision is imminent (where another vessel is dragging on
to own vessel at anchor, etc) the Bridge team tend to be
intent on picking up the anchor. This will only result in
precious time being lost and will do very little to avert an
impact.
In such cases losing the anchor and chain is far less
expensive and damaging than a collision. So if the situation
warrants DO NOT HESITATE to slip the anchor.
Foul Anchor
An anchor which has become entangled or caught up in
something is known as Foul Anchor.

Action in case of anchor fouled by underwater obstruction

Vessel is moved ahead under engines, veering cables until it

grows well astern.
When the vessel is brought upto with the cable growing
astern, and the cable is taut, then work the engines ahead
slowly and see if the cable breaks out slowly.
In case it does not break out then steer the vessel slowly in
an arc towards the anchor and try to rotate the anchor and
break it out by constant movement.
If still unsuccessful then try the above procedures using
astern movements.
If still not successful then rig up an anchor buoy and slip cable
for later recovery.
Action in case of anchor fouled with wire cable etc
Anchor and fouling to be hove well up into the hawse pipe.
Use a fibre rope and pass it round the obstruction and heave
both ends taut and make fast on the forecastle deck near
maximum flare.

Walk back anchor clears of obstruction.

Heave the anchor into the hawse pipe.

The obstruction which is now clear of the anchor can be

released by slipping the fibre rope.
 HANGING-OFF AN ANCHOR
PURPOSE OF OPERATION

To remove the anchor out of the hawse pipe and enable the vessel to
be moored to a buoy or towed using the anchor chain through the
hawse pipe.
MATERIALS REQUIRED FOR A 10 TONNE ANCHOR

1. 3 Nos of 30 mm wire (SWL 6.0 tonnes) - For 1st Easing wire

2nd Easing wire
Preventer wire
2. shackles with SWL of 6 tonnes

3. Other tools required to carry out the operation as per normal

seamanship practices.
SEQUENCE OF OPERATION:

1. Walk back the anchor clear of the hawse pipe.

1. Secure one end of the easing wire on the mooring bit.

2. Pass the other end through the panama lead, through the
anchor crown D shackle (as a bight) and back through the
Panama lead on to the warping drum of the windlass.
3. Rig a preventer wire (as a bight) through the anchor
crown D shackle, pass it through the fairlead well forward
and secure it on the mooring bits.
4. Ensure there is sufficient slack on the preventer wire.
6. Slack on the anchor chain until the preventer becomes taut
and the 1st easing wire is up and down and the anchor is
under the shoulder.

7. Continue to walk back the chain until the next joining

shackle is on the deck.

8. Heave on the 1st easing wire and secure the anchor in the
up and down position.

9. Rig up the 2nd easing wire forward of the joining shackle

(on a bight) and take up the weight of the chain.

10. Break the joining shackle.

11. Walk back the 2nd easing wire to bring the end of the
cable clear of the hawse pipe.

12. Recover this end of the cable using rope hawsers

through the Panama lead.

13. Now walk back the anchor chain through the hawse
pipe and the cable is now ready for towing or mooring
operation.