Lifeboat Davit System Product

Overview

A lifeboat davit is the mechanical infrastructure for launching and recovering lifeboats on merchant and military vessels. It is a ship-mounted articulated crane with a hydraulic boom, electric winch, and dual fall ropes that swing the boat from its storehouse on deck, lower it to the water surface, and recover it when the evacuation ends or the rescue is complete. Modern davits are hydraulically actuated for smooth operation and equipped with redundant safety interlocks and load monitoring to prevent capsizing or dropping the boat. They are essential equipment under SOLAS (Safety of Life at Sea) regulations and must be certified by a classification society and routinely inspected.

The system comprises a [[lifeboat-davit-boom|hinged steel boom]] pinned to a [[lifeboat-davit-pivot-base|ship-mounted pedestal with a slew bearing]] that allows 360° rotation. The boom extends outboard via a [[lifeboat-davit-hydraulic-system|hydraulic cylinder]], positioning the [[lifeboat-davit-pulley-block|pulley blocks]] above the boat. A [[lifeboat-davit-winch|motor-driven winch]] on deck reels in and pays out two [[lifeboat-davit-falls|synthetic or wire rope falls]] that pass through the blocks and attach to the boat's lift lugs. The operator stands at a [[lifeboat-davit-control-station|control panel]] on the bridge or lifeboat deck, using a wireless [[lifeboat-davit-control-pendant|pendant]] to raise, lower, and swing the boat. [[lifeboat-davit-limit-switches|Limit switches]] and [[lifeboat-davit-load-cell|load sensors]] prevent over-extension, collision, and overload failures.

How it works

The davit operates through coordinated hydraulic and electric actuation. When the boat is slung (rigged with its weight hanging on the falls), the operator cannot swing the boom outboard—a [[lifeboat-davit-load-interlock|load interlock]] senses the rope tension and locks out the azimuth hydraulics. The first action is always to hoist the boat clear of the deck using the winch motor. The Motor draws power from the ship's electrical service, driving the Reduction Gearbox which spins the Winch Drum at 20–40 RPM. As the drum rotates, it winds rope off the sheaves in the Pulley Block Assembly, lifting the boat with a 2:1 mechanical advantage—the load cell in the winch line shows the tension climbing from zero to the boat weight plus personnel.

Once the boat is clear of the deck, the operator can safely swing the boom outboard. The Boom Extension Cylinder receives pressurized hydraulic fluid from the Control Valve, extending and pushing the upper boom outward. The boom angle increases from stowed (inboard at about −30°) toward water-reach (about +70°). As the boom swings, the [[lifeboat-davit-boom-lifting-lugs|boom lifting lugs]] at the tip move outboard and downward, positioning the pulley blocks above the water and away from the ship's hull. The [[lifeboat-davit-limit-switch-lower|boom lower limit switch]] stops extension at maximum reach to prevent collision with the ship's structure or rigging.

With the boom outboard and the boat hoisted clear, the operator opens the Control Valve to divert pump flow through the winch motor in the descent direction. The Winch Drum begins to rotate in the pay-out direction, and the boat descends toward the water at a speed governed by the proportional opening of the control valve—typically 0.3–0.5 m/s, slow enough that crew can stop the descent instantly if an obstruction is spotted. The Load Cell continuously measures rope tension, and if the weight suddenly drops—indicating the boat has touched the water—a [[lifeboat-davit-limit-switch-down|load-sensitive limit switch]] automatically engages the [[lifeboat-davit-drum|drum brake]] to arrest the descent and prevent slack rope, which could tangle in the davit.

The boat's crew then releases the fall hooks from the boat's lift lugs, signaling the bridge. The davit is now unloaded, and the Load Interlock unlocks the boom rotation. The boat is free to motor away, and the davit boom retracts inboard via the boom cylinder. Recovery of the boat follows the opposite sequence: the boat approaches the davit from astern at bare steerage, crew attach the fall hooks, the winch hauls the boat toward the boom with a steady low-speed hoist, and the boom swings inboard as the boat rises, positioning it above the stowage cradle. The operator then lowers the boat gently onto the chocks until the load cell reads zero, confirming the boat is fully seated and the davit is unloaded.

Safety interlocks and redundancy

Davit safety depends on multiple independent systems working together. The [[lifeboat-davit-load-interlock|load interlock]] uses a pressure switch sensing hydraulic tension in the boom cylinder; if rope load is non-zero, the valve holding the boom azimuth hydraulics is de-energized, and the boom cannot move. The Relief Valve protects the hydraulic system from overpressure if the operator commands a conflicting action. The [[lifeboat-davit-accumulator|accumulator]] stores energy from the pump; if ship power is suddenly lost during descent, the accumulator supplies enough flow to continue the descent under the [[lifeboat-davit-control-valve|control valve]], allowing the boat to reach the water safely rather than hanging on a stopped winch.

The [[lifeboat-davit-drum|drum brake]] is spring-applied and pump-release: in its natural state, it is engaged, holding the rope; only when the pump pressurizes the brake release circuit does the drum spin freely. If the pump fails or loses power, the spring automatically engages the brake and holds the load. The [[lifeboat-davit-limit-switch-up|upper limit switch]] on the winch prevents over-hoisting and drum rope slippage. The [[lifeboat-davit-limit-switch-lower|boom lower limit]] is both a mechanical hard stop and a switch that disables further extension. These redundancies ensure that a single failure—loss of power, control valve jam, or human error—does not result in a falling boat or pinned crew.

Maintenance and certification are mandatory: SOLAS requires annual proof-load testing at 1.25× SWL, visual inspection of all welds and pins, rope diameter measurement (rope must be renewed if it shrinks more than 5%), brake function testing, and load-cell calibration. A davit that fails any test must be tagged out-of-service until repairs are made and retested.