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ANCHORING THE SHIP

Updated on April 10, 2013

There is a saying among Sailors “People come & people go, but ships they never stop sailing for anybody”. If the Ship is built & launched, until it goes for scrap it sails & sails.

The only moment ships stay at sea is only during Anchorage. The ships are anchored for the following reasons. Sometimes the ships come to the port & they have to wait for their turn to load or discharge the cargo. In the other case the berth may be occupied by another vessel. The world’s economy impacts the shipping industry very badly. Running a ship can be very expensive. If the owner doesn’t get a good freight it is useless to sail the ship. There are also situations where cargo is not available. When the USA brought economic sanctions on Iraq their ships couldn’t sail in USA, Europe & Far East. The Iranian ships were not chartered.

Anchoring can be done only in appropriate depths. In deep waters anchoring is not possible. These formulae are basics for anchoring depths.

Minimum depth for anchoring= 4 x Ship’s draft

The number of shackle to pay out= 1.5 x √depth

There are many types of anchors & their weight varies according to the Ship’s size. An aframax tanker vessel may have an anchor around 14 tons.

The anchor consists of two main parts, which are Crown & Shaft. The crown consists of two flukes which can swing 45 degrees on either side. At the end of the shaft a “D” shackle connected. Then the “D” shackle is connected to the anchor chain via the swivel.

Anchor chain consists of cables which are divided into shackles. The shackles are identified by Lugless joining shackles. Each chain consists of 12 or 13 shackles. The standard length of a shackle is 27.5 meters (90 feet/15 fathoms). The end of the anchor chain is connected to the ship via the Bitter end. The Bitter end is a point where you can let go the anchor & its chain to sea in case of Emergency.

Once you let go the anchor the fluke gets submerged into the sea bed. The shaft lies on the sea bed & some amount of anchor chain also lies on the sea bed. All these together give the holding power to the anchor. The anchor flukes alone cannot hold the ship. For example if the Shaft is lifted by 5degrees from sea bed it loses 20% of its holding capacity, 10 degrees from sea bed it loses 40% of its holding capacity, 15 degrees from the sea bed it loses 60% of its holding power.

When letting go the anchors ships have to be given little amount of stern movement to avoid chain coiling in one place.

Before anchoring the following things should be considered.

The position where you are going to anchor your vessel should be decided. The swinging room at that place should be checked. Because once you dropped your anchor the vessel will swing around it. The depth at that place should be checked. The particular position should be traffic free. The consideration for the holding ground also plays a big part. For example the best holding ground is known as Blue Clay. The mud, clay etc holds the vessel very well. But the rock, ooze, sand etc do not hold the vessel very well. The position charted should be free of any under water obstructions. If you drop your anchor on a submarine oil pipe line the vessel is going to get arrested & heavy penalties to be fined. In some severe cases the Master of the ship could be imprisoned.

There are many types of anchoring methods. The common one is using single anchor which is known as single anchor operation.

If you drop both the anchors there are high chances that when the vessel swings anchor cables may get entangled, which is known as anchor hawser fouling.

If you are serious & want to drop both the anchors very particular attention should be given to tidal flows & currents. There are three methods for dropping both the anchors, they are Running moor, Standing moor & Open moor.

After anchoring you have to confirm whether the anchor is holding. This is known as “Brought up”. By watching the cable after applying the brake, if the cable rises up to a long stay & then bows to form a Catenary, then rises again the vessel is riding to her anchor & anchor is not dragging.

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