Windlass

What makes a windlass different from a warping winch

A windlass is built around a chain wheel (also called a cable lifter or gypsy) whose pockets are cut to exactly match the ship's stud-link chain size, so the chain engages positively without slipping under load. A plain mooring winch, by contrast, works a wire or rope drum by friction and has no chain-handling capability at all. Most windlasses combine both functions on a common shaft - chain wheel on one side, warping or mooring drum on the other - driven by an electric or hydraulic motor through reduction gearing, with a band brake on the chain wheel to hold the anchor once it is out.

Main components

Chain wheel (cable lifter)

Matched to chain diameter and grade; a worn or mismatched wheel lets the chain jump pockets under load, the single most common cause of chain damage at the windlass.

Band brake

Holds the anchor and chain stationary once let go to the working depth; must hold well above the anchor's weight in water plus a length of chain, since the ship's motion adds dynamic load beyond the static weight.

Drive motor and gearing

Electric motors are common on smaller ships; hydraulic drive is preferred where high torque at low speed is needed, such as heaving in against a taut cable.

Warping or mooring drum

A friction drum on the same shaft used for handling mooring lines, sized for the line diameter and pull the mooring arrangement requires.

Chain stopper and spurling pipe

The chain stopper takes the static holding load off the windlass once anchored, so the brake is not left carrying the full load indefinitely; the spurling pipe guides the chain into the chain locker.

Selection and sizing

Sizing follows directly from the anchor and chain specified for the ship's equipment number under class rules: chain wheel diameter and pocket profile must match chain size and grade, and rated pull and hoisting speed must handle the anchor and chain weight for the vessel's design depth. Motor power is set to heave the anchor and a specified length of chain at a minimum speed, typically around 9 metres per minute for the heaviest condition specified by class.

Regulations and class

Class rules derive the required anchor and chain specification, and therefore windlass rating, from the ship's equipment number, which is calculated from displacement, breadth and superstructure area. The windlass, chain and anchor are tested together during sea trials, and class surveys check brake holding capacity and chain wheel condition periodically. IACS Unified Requirements set the calculation basis for equipment number and anchoring equipment that class societies apply.

Typical faults

• Worn chain wheel pockets - chain rides up and jumps under load, causing shock loading on the brake and chain stopper and accelerating chain wear.
• Brake lining wear or oil contamination - reduced holding torque risks the anchor running out uncontrolled, especially in deep water where cable weight builds quickly.
• Gearbox oil contamination with seawater - spray ingress through worn seals corrodes gears and bearings, eventually causing gear tooth failure under load.
• Motor overload on heavy cable recovery - undersized or degraded motor windings trip on thermal overload exactly when full power is needed to break the anchor out of the seabed.
• Chain stopper misalignment - a stopper not correctly seating leaves the full riding load on the brake, which is not designed to hold indefinitely and can slip or overheat.

What to look for in a supplier

• Chain wheel profile certified for the exact chain size and grade fitted, not just a nominal diameter match.
• Documented brake holding capacity test results against the class-required load.
• Spares support for gearbox and brake components matched to the actual installed model.
• Hydraulic power unit compatibility if replacing a hydraulically driven windlass, since power unit and motor must be sized as a matched pair.

Never rely on the windlass brake alone to hold the ship at anchor overnight - engage the chain stopper once the required scope is out, and let the stopper, not the brake, carry the static load.