A windlass is any device used to move considerably heavy weights using a pulley system. A barrel with a chain or cable wound around a shaft, that is operated using a belt or crankshaft. This shaft provides a circular motion that can lift heavy weights without having to expend the energy needed to normally haul it.
The crank can either be operated manually (as in the case of drawing water from wells) or using a motor (used in large construction cranes) and is attached to the barrel in such a way that it can rotate about a central axis. The principle behind using a pulley design is that large weights can be lifted by distributing the load between multiple cables instead of a single chain.
Thus, by exerting a limited amount of effort, a considerably heavier load can effectively be raised. The issue with using such types of designs is that a large strain is placed on the cable or chain used to shift the load. In case the mechanism is stopped midway through the operation, adequate steps have to be taken to prevent the cable from breaking under tension.
Most materials can suffer from fatigue or stress-related failure under loads of tension. Thus, for an anchor windlass that has to lift a weight of nearly a ton, specialized mechanisms have to be used to ensure that the weight of the anchor head is taken off the anchor rod while the operation is stalled.