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Maritime Forum

TOPIC: Purpose of Devil's claw, Cable stopper, Hatch Coaming and Duct Keel

Purpose of Devil's claw, Cable stopper, Hatch Coaming and Duct Keel 17 Jul 2016 14:39 #4590

This Question I am putting on behalf of Hassan Khalid, who requested Answer to this question on WhatsApp.

Q. Explain the meaning of Following terms with simple sketches and their purpose in the Structure of ship.
  1. Devils Claw
  2. Cable stopper
  3. Hatch Coaming
  4. Duct Keel
  5. Collision Bulkhead
Last Edit: 17 Jul 2016 14:43 by anandgardener.
The administrator has disabled public write access.

Purpose of Devil's claw, Cable stopper, Hatch Coaming and Duct Keel 17 Jul 2016 15:04 #4592

1. Devil's Claw :

It is a securing device used to secure the anchor cable, when the vessel is at sea.

It is in addition to the Anchor Chain stopper and the Band brake to fasten the Anchor chain in high seas, where sea may be voilent and in severe pounding heavy load may come on the Cable stopper and thus it shares the load of anchor and chain along with the Cable stopper.( In the sea, the Anchor windlass is disengaged from the Prime mover and the chain is offloaded from the Cat-wheel and the load is taken on the Cable stopper)

The construction of devil's claw is below. By using the Turnbuckle it is made loose and tight to be fitted to the Anchor chain.

Cable stopper
It is the fitting used to secure the anchor chain when riding at anchor(i.e. Anchor stowed and the ship is sailing), thereby relieving the load on the windlass, and also for securing the anchor in the housed position in the hawse-pipe.

Chain stopper usually consists of two parallel vertical plates mounted on a base with a pivoting bar or pawl which drops down to bear on a chain link.

A hinged bar is fitted in the chain stopper which may be dropped between two links of the chain in order to prevent the chain from running out when the windlass brake is released.

Hatch Coaming

The merchant ships have cargo holds to carry cargo(and earn the money by freight).

Now the top of the hold should be open to load and unload the cargo in the cargo spaces (in case of dry-cargo ship)and when such opening is made on the top deck, the top deck becomes structurally weak. This is been compensated by the Construction of Hatch Coaming.

It also provide a support to the Hatch Cover and makes the opening to the Cargo Hold on a certain height, so that primarily it saves the Hatch Cover from the water coming on deck.


The Hatch coaming extends quite below the deck level to provide the structural strength to the deck opening.

Below and above the deck it is often connected via bracket plates and beam to the Deck(as shown in figure below)

Duct keel

Duct keels are provided in the double bottoms of some vessels. These run from the forward engine room bulkhead to the collision bulkhead and are utilized to carry the double bottom piping.

The piping is then accessible when cargo is loaded, an entrance to the duct being provided at the forward end of the engine room.

No duct is required aft of the engine room as the piping may be carried in the shaft tunnel. A width of not more than 2.0 m is allowed for the duct, and strengthening is provided at the tank top and keel plate to maintain continuity of strength of the transverse floors(vertical plates in double bottom).

To get an idea of how the Duct keel is, watch the below video

Collision Bulkhead

SOLAS, The International Convention for the Safety of Life at Sea, requires that ships are fitted with transverse watertight bulkheads to provide the ship with a certain measure of survival capability should the hull be penetrated and the vessel suffering water ingress as a result.

The most forward bulkhead is called the collision bulkhead and is meant to be a second barrier in a collision resulting in bow plate rupture and water ingress to the forepeak area.

The collision bulkhead must be located not less than 0.05L or 10 metres, whichever is the lesser from the forward perpendicular , and not more than 0.08L or 0.05L+3 m, whichever is the greater (SOLAS 2014, Ch II-1, Reg 12.1).

The regulations require that the bulkhead is watertight from the bottom of the ship, up to the bulkhead deck. The collision bulkhead may have steps or recesses, but no doors, manholes, access openings, ventilation ducts or other openings can be fitted in the bulkhead below the bulkhead deck. There is only one exception and that is a single pipeline which is allowed to penetrate the bulkhead for the purpose of filling and emptying the forepeak tank.

Last Edit: 17 Jul 2016 17:15 by anandgardener.
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