Capstan

A capstan is a machine for applying pulling power to ropes, consisting of a drum, or barrel, that rotates about a vertical axis on the deck. A rope or mooring line is given several turns around the revolving drum, and as the capstan turns, friction between the rope and the drum lets the machine haul in the line while a crew member tends the tail, taking in the slack; the more turns and the greater the tension held on the tail, the more grip and pulling force is developed. This principle (heaving a line by turns around a powered drum) is the same as that of the warping drums on a mooring winch.

The capstan's defining feature is its vertical axis, which sets it apart from the windlass and from horizontal-drum winches. In the age of sail, capstans were turned by hand, with sailors pushing on bars fitted into the head and walking round it to raise the anchor or heave heavy loads, and the rhythmic songs called sea shanties were sung to coordinate this effort. On modern ships the capstan is powered hydraulically or electrically and is used mainly for handling mooring lines (heaving a ship alongside, warping it along a quay, or tending lines) and sometimes as part of the anchor-handling arrangement at the stern.

Because it deals with mooring lines under tension, the capstan carries the same hazards as other mooring equipment: lines can part and snap back, and hands and clothing can be caught in turns around a turning drum, so it must be operated with care and good communication. Capstans, windlasses and mooring winches together make up the deck machinery by which a ship handles its anchors and secures itself to a berth, and the capstan's simple, effective design has kept it in use for centuries.