davit

A davit is a lifting crane mounted at the edge of a platform, deck, or building facade, designed to lower and raise loads over a drop. The structure projects outward from the support surface, allowing loads to swing clear of the structure beneath. Davits are built from structural steel, typically tubular or I-beam construction, and range in capacity from a few hundred kilograms for window-cleaning rigs to 20 tonnes or more for lifeboat systems on large vessels.

The classic davit configuration uses two units working as a pair, positioned at equal distances from the edge. Each davit carries half the load through its own hoist mechanism, usually a wire rope winch with manual, hydraulic, or electric drive. On ships, paired davits are mounted perpendicular to the hull amidships or at the stern, their arms angled outward so a suspended lifeboat clears the railings when lowered. On buildings, window-cleaning davits may use a single articulating arm that can pivot and telescope to reach different facade sections.

The davit arm itself comprises a boom (the primary structural member) and a hoist point at its free end. The boom connects to a base support through either a trunnion bearing (for fixed-angle arms) or a slewing ring (for rotating arms). The angle of the arm, typically 40 to 60 degrees from horizontal on marine davits, is set by the manufacturer to balance reach with structural stability. Wire rope runs from the winch, over a pulley at the boom tip, and down to the load.

Failure modes and limitations

Davits fail most often through inadequate maintenance of the wire rope, which corrodes and frays when exposed to salt spray or weather. The hoist brake, a critical safety component, can become unreliable if not serviced according to inspection intervals. Overloading is a persistent hazard on older systems where load limits are not clearly marked. Structural cracks develop at weld points, particularly where the boom connects to the base, under repeated cycles of load and wind movement. Entanglement of personnel in suspended loads or ropes remains a significant operational risk.

The term davit derives from the Old French word davie, possibly linked to a proper name, though the exact etymology is disputed among maritime historians. It has been standard maritime vocabulary since at least the 17th century. Outside of shipping, davits appear in construction under different regional names: European facade-access systems may be called window-cleaning davits or simply suspended access cradles, while the portable counterparts used in salvage and rigging are sometimes called shear legs or A-frames. All variants share the same fundamental principle: a cantilevered beam structure that places the load laterally away from the supporting structure.