Types of Lifeboat Release Mechanisms

Lifeboats are launched from a ship during testing or at the time of extreme emergencies (major fire, flooding, etc.), only on the verbal announcement of the master.

In common, both these mechanisms release the lifeboats from the davit that is attached to the falls (wire) by means of the hook and set the boat free to move away from the ship.

For launching a lifeboat there are two main types of lifeboat-releasing mechanisms, such as:

1. Off-load Release
2. On-load Release

Off-Load Release:

• Off-load release means that the load of the lifeboat is 'OFF' from the hooks.

• In this method, the lifeboat is lowered and it is completely waterborne.

• Once the lifeboat is waterborne the water pressure acts on the diaphragm of the hydrostatic release unit that is placed underneath the lifeboat's hull.

• This water pressure moves the coxswain release handle in a Green position.

• Safety Pin needs to be removed.

• Now the hand lever can be pulled to release the hook and the lifeboat is released from the fall.

• Now lifeboat is free to move away from the vessel.

On-load Release:

• On-load release means that the lifeboat is still in the fall which means the load of the lifeboat is 'ON' the hooks.

• The lifeboat is not waterborne rather it is lowered to just above the water level so that once the lifeboat is released from the hooks it will not hamper the crew inside and will not cause any damage to the lifeboat's hull.

• To operate the coxswain release handle the interlock is to be removed from the hand lever by breaking the protecting glass.

• Now the indication is moved to the green side and now the hand lever can be pulled from inside to release the hooks hence the lifeboat is set free. 

Free Fall Lifeboat Release:

• The freefall lifeboat release mechanism is as similar to the On-load release.

• The major difference is the freefall lifeboat is launched from the stowed position by operating a lever located inside the lifeboat whereas in an on-load release the lifeboat is lowered to just above the water level and then released to water.    

• Each free-fall lifeboat shall be of sufficient strength to withstand when loaded with its full complement of persons and equipment, a free-fall launch from a height of at least 1.3 times the free-fall certification height. 

(Free-fall Certification Height - It is the greatest launching height for which the lifeboat is to be approved, measured from the still water surface to the lowest point on the lifeboat when the lifeboat is in the launch configuration.)

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Reference: 

1. IMO Publications & Documents - International Codes - LSA Code
2. IMO Publications & Documents - Resolutions - Maritime Safety Committee - Resolutions.MSC.48(66).