Liferaft Davit

What sets a liferaft davit apart from a lifeboat davit

A liferaft davit exists for one job: swing a stowed raft canister out over the ship's side and lower it to the embarkation deck or the waterline, either under gravity once the arm is released or via a small hydraulic or electric ram. It does not need the load capacity, brake rating or wire-fall speed of a lifeboat davit, because a liferaft canister weighs a fraction of a loaded lifeboat and does not need to be recovered under power in the same way. Many liferaft davits are single-arm, davit-launched arrangements fitted specifically for a raft that would otherwise have to be thrown or float-free released, most often where deck height or arrangement makes a simple throw-overboard launch unsafe or where SOLAS requires a davit-launched liferaft as one of the vessel's survival craft.

Main components

Arm and pivot

A single tubular or fabricated steel arm pivots outboard from a deck-mounted trunnion, swung out either by a hand crank, a falling weight arrangement, or a small hydraulic cylinder. The stowed position locks the arm inboard against a gripe or stop to keep it secure in a seaway.

Winch and wire fall

A wire fall runs from the winch drum through a sheave at the head of the arm down to the raft's lifting hook. The winch carries a mechanical brake that must hold the loaded raft stationary at any point of lowering and must not allow uncontrolled free-fall. Some installations use a hydrostatic or centrifugal speed governor instead of a hand brake to cap descent speed.

Painter and hook release

The raft's painter line is secured on deck before launch so that it remains attached and triggers automatic inflation as the raft goes over the side. The lifting hook is released once the raft is waterborne, usually a simple manual release rather than the load-release-under-tension gear fitted to lifeboat falls, since the raft does not need to be recovered by the same davit in a rescue scenario.

Selection and sizing

Sizing is driven by the raft canister weight and the launch height, not by passenger capacity in the way a lifeboat davit is sized:

• Safe working load must exceed the heaviest canister the davit will ever carry, with margin for the wet weight after the raft inflates alongside.
• Outreach must clear the ship's side, including any flare, fendering or overhanging structure at the embarkation deck.
• Lowering speed must fall inside the range the raft's inflation and painter system is designed for too fast risks damage to the raft on entering the water.
• Manual backup operation is required in case power or hydraulic pressure is lost, typically a hand crank or a gravity-release fallback.

Regulations and class

Where a vessel's survival craft arrangement under SOLAS Chapter III calls for a davit-launched liferaft rather than a throw-overboard raft, the davit itself falls under the same LSA Code performance requirements as other launching appliances: load testing, an operational test under load at defined intervals, and a full davit and winch overhaul on a class-set cycle, commonly five years, with load testing at a fraction of that interval in between. The winch brake is subject to a static and dynamic load test as part of that overhaul, and the wire falls are renewed on a condition and calendar basis rather than run to failure.

Typical faults

What to look for in a supplier

• LSA Code type approval covering the specific davit and winch combination, not the davit alone.
• Documented safe working load matched to the actual raft canister weights carried on board.
• Spare parts availability for the winch brake and wire falls, which are the components replaced most often.
• Overhaul and load-testing service recognised by the vessel's class society.

Check that the gripe or securing pin is actually released before the drill starts a davit swung against a still-secured gripe is a recurring cause of bent arms during liferaft drills.