Anchor Winches and Windlasses

Anchor Winches and Windlasses pay out, haul in and hold each mooring leg on a moored drilling unit. The Category covers chain windlasses with wildcats, wire drum winches, combination chain and wire winches, traction winches, chain stoppers and the fairleads that turn each leg down to the seabed, with their drives, brakes and controls.

How the machinery works

A windlass grips chain in the pockets of a wildcat, also called a cable lifter, and drops it into a chain locker. A drum winch stores wire in layers on a grooved drum. A combination winch carries a wildcat and a drum on one frame for chain and wire legs. During drilling, a chain stopper or the brakes hold the leg, so the gearing does not carry the static load. Electric drives, often with frequency converters, give fine speed control during tensioning. Hydraulic drives are common on older or smaller units.

Configurations

Type	Line handled	Notes
Chain windlass	Stud link or studless chain	Wildcat pockets suit one diameter and type
Wire drum winch	Six-strand mooring wire	Drum capacity limits leg length
Combination winch	Chain and wire on one machine	Common on semi-submersibles
Traction winch	Wire through traction sheaves with a storage drum	Keeps high tension off the storage drum
Chain jack	Chain pulled in steps by hydraulic cylinders	Mostly for long-term moorings

MacGregor, which took over the Pusnes mooring range, is a common OEM on drilling units.

Key specifications

Parameter	Why it matters	Typical classes or units
Chain size and grade	Wildcat pocket fit	mm (in), R3 to R5
Wire diameter and drum capacity	Leg length and spooling	mm (in), m (ft)
Rated pull	Tensioning speed and load	kN or tonnes-force at stated speed
Brake holding capacity	Must hold the leg's design load	kN or tonnes-force, often as a share of chain MBS
Drive	Power supply and control	Electric AC or DC, hydraulic
Instrumentation	Tension and length for the mooring system	Load cells, chain counters

Standards and class

DNV-OS-E301 sets design loads for windlasses, winches, stoppers and fairleads, including brake capacity measured against the MBS of the line. ABS and other societies have equivalent rules for position mooring. Class normally certifies mooring winches on a classed moored unit, witnesses brake and load tests and surveys them at intervals. API RP 2SK sets the line tensions the machinery must hold.

Failure modes and inspection

Wildcat pockets wear and lose their grip on chain links. Measure pocket profiles against the OEM drawing with templates.
Brake linings wear and glaze, and drums or discs score and crack. Run a static brake holding test at the rated load.
Gear teeth pit and wear, and bearings fail. Ask for oil analysis history and inspect teeth through access covers.
Chain stoppers wear on the pawl or bar that bears on the link. Check the bearing faces and the pin.
Fairlead pockets, sheaves and bearings wear and seize. Check rotation, swivel action and groove wear.
Foundations and seatings crack under cyclic load. Ask for the last NDT of the foundation welds.
Load cells and chain counters drift. Ask for calibration certificates.

Documentation

Class certificate and design approval for the machine.
Brake test and load test reports, with the loads applied.
OEM service history and overhaul reports.
Gearbox oil analysis records.
Load cell calibration certificates.
General arrangement drawing, with foundation and fairlead details.

Integration

Match the wildcat to your chain diameter and type before anything else. Then check that the foundation footprint and deck strength suit the machine, and that the drive suits your power supply, whether AC or DC electric or hydraulic. The tension and length signals must also reach your mooring monitoring system. A combination winch only works if the chain-to-wire connector passes through its fairleads and over its wildcat.

Overhaul and the used, surplus or refurbished choice

An overhaul renews brake linings, seals and bearings, inspects or replaces gears, re-machines or replaces the wildcat, and finishes with a witnessed brake and load test. A used machine that matches your chain size and foundation is often the quickest replacement. Unused surplus windlasses from cancelled hulls suit sister rigs. The line the machine runs is in Anchors and Chains, and smaller deck winches are in Winches and Capstans.

FAQ

Frequently asked questions

Can a used windlass run a different chain size?

Only with a new wildcat made for that chain diameter and type. Studless chain also needs a different wildcat from stud link chain. Check that the brakes, gearing, stopper and foundation suit the new chain's breaking strength as well.

What tests should a used mooring winch pass before service?

A used mooring winch should pass a static brake holding test, a load test and a functional test of controls and emergency release, usually witnessed by class. Calibrate the load cells and chain counters first. Check wildcat wear and gearbox oil before loading the machine.

What is the difference between a windlass and a mooring winch?

A windlass grips chain on a pocketed wildcat, while a mooring winch stores wire rope on a drum. Combination winches carry both and handle chain and wire legs. Traction winches pull wire through sheaves and keep the high tension off the storage drum.

Why does a moored rig hold its legs on stoppers instead of the winch brake?

A chain stopper takes the static leg load directly into the structure, so the brakes and gearing are not loaded for weeks at a time. That reduces wear and adds a second holding device. Class rules set the stopper's design load against the chain's breaking strength.

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