Davit System (Lifeboat/Raft)

What a davit system does and how it differs from the boat it launches

The lifeboat or life raft gets the survival craft to the water; the davit is the separate machine — winch, wire falls, davit arms, and release hooks — that lowers it there under control and recovers it afterward. Gravity davits, the type fitted for most lifeboats, use the boat's own weight to swing the arms out and lower it, with the winch brake controlling descent speed; the winch is also used to hoist the boat back on board under power. Davit-launched liferafts use a simpler single-arm or radial davit purely to lower a raft that has already inflated, with no recovery function normally fitted. Free-fall lifeboats dispense with a lowering davit altogether, launching by dropping the boat down a ramp, which changes the failure modes entirely since there is no wire fall or brake to maintain.

Main components

• Davit arms and structure — swing or slide out from stowed to launch position, carrying the full weight of the loaded boat at the outboard position
• Winch and brake — controls lowering speed and provides the power hoist for recovery; the brake must hold the loaded boat stationary at any point in the descent
• Wire falls — the wire ropes from winch to boat, subject to their own discard criteria for broken wires, corrosion and diameter reduction
• On-load and off-load release hooks — release the boat from the falls either under load, just before or at the moment of waterborne contact, or only once fully waterborne and off-load, depending on hook type
• Limit switches and interlocks — stop the winch at the stowed and fully lowered positions and prevent hoisting with the hook still engaged incorrectly

Selection and sizing

Davit selection follows the survival craft it serves, not the other way around: safe working load must exceed the fully loaded boat weight (boat, full complement, equipment and provisions) with the class-required margin, and the davit's outreach and headroom must clear the ship's side and any structure below at maximum roll and trim. Winch power and brake capacity are matched to the loaded weight and the lowering speed required to launch within the time SOLAS allows for the vessel's crew complement.

Regulations and class

Davit systems are covered by the IMO LSA Code together with SOLAS Chapter III, which set launching time, davit strength margins, and release gear design requirements, including tightened design and testing standards for on-load release mechanisms introduced after a series of on-load release hook accidents. Class and flag require an annual thorough examination of the davit and winch, an operational test of the on-load release gear, and a dynamic winch brake test at five-year intervals, with davit falls turned end-for-end or renewed on a running-hours or age basis per the maker's instructions.