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August 1, 2001

 

 

 

 

THE GRAVITY DAVITS
FOCUS Know About - July 11, 2001
Source : Survival at Sea The Lifeboat and Liferaft
by CH Wright, National Sea Training Schools ( Liverpool, Retired)

Gravity davits are any davits that use the weight of the boat to do the work required to launch the boat overside, and may be on pivots, or have a carriage mounted on roller-track ways which are fixed either to the deck or overhead. The boat is launched by the lifting of a brake handle.

This brake is required to apply automatically immediately it is released by the operator. The rate of the boat's descent must be controlled by an independent centrifugal brake.These davits must be fitted with wire rope falls and winches,and be

able to launch a boat againts an adverse list of 25 degrees and must be fitted with tricing pendants o bring the boat alongside and with bowsing-in tackle to replace the tricing pendants and keep the boat alongside. The tricing pendants must always be released and the weight of the boat transferred to the falls before persons are embarked in the boat.

Gravity davits are provided with a safety device which will prevent the davits from operating while it is in position. This device often takes the form of a trigger to which the gripes are attached, and is so adjusted that while the gripes are on, the davits cannot operate. In addition on some gravity davits holes are provided into which a bolt can be shipped to prevent the davits working, these bolts known as "Harbour safety pins" are to be shipped only when the falls and winches are being overhauled. Harbour safety pins are always to be unshipped whenever the vessel is at sea, so that the boats are at all times ready for use.The Wellin overhead "Devon" gravity davit has a moving embarkation platform, on which the controls are mounted, incorporated in the davits which are mounted on roller tracks. Embarkation can be undertaken when the boat is stowed, or at any point between the stowed and fulloutreach positions.

Until the actual lowering of the boat into the water it is rigidly held in the davit carriage, and cannot rock or sway under away circumstances, even when the ship is going at full speed. No tricing pendants or bowsing-in tackles are required, and the launching can be done by a single operator either from within the lifeboat, or from the platform.

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