Anchoring of Vessels

Anchoring of Vessels is as frequent operation on board .But in spite of that, the number of incidents related to anchoring never seem to reduce. let us discuss a practical way of anchoring, 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.
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. 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 has published a graphical relation between this angle and holding power of anchor.
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.
3. Preparing for Anchoring
Preparing the vessel for anchoring can start days before arrival. 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. 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 , attention should be paid to the chart symbol ‘#’. T
4. Anchor stations
Anchor stations should be ready forward well in advance. The anchor party should make the inspection of the anchor windlass, Hydraulic power packs or electric power is running. The lashing of both the anchors should be removed.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 .
If Master feels the ship’s speed is much more than what it should be, he should exercise zig-zag maneuver (also called rudder cycling) to reduce the speed, bring the vessel to this heading at least 1 mile from the anchoring position. engine movements should ensure that vessel’s speed is less than 2 knots about half a mile from the anchoring position. nce 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.
6. Anchoring Methods
there are two ways an anchor can be dropped to the seabed.
By letting go
by walking back.

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