Capstan

A powered rotating drum that moves rope by friction as the rope wraps around it, allowing sustained pulling without winding the rope onto the drum.

Capstan equation: An equation describing how friction around a curved surface changes tension between the two ends of a rope. It quantifies the tension multiplication that lets a capstan pull heavy loads.
Windlass: A horizontal-axis machine for hauling or lifting using a drum or chain wheel. Ships use windlasses to raise anchors, often with a capstan-like rope or chain grip.
Rope: A thick, flexible line made by twisting, braiding, or laying fibers or strands together. A capstan acts on rope through contact and friction rather than by fastening its end to a coil.
Sailing ship: A vessel propelled primarily by sails acting on wind. Capstans became essential aboard sailing ships for hauling anchors and heavy lines.
Friction: The resistance to relative motion between surfaces in contact. Friction between rope and drum transfers the capstan’s rotation into rope movement.
Mooring: The securing of a vessel to a fixed point or another vessel. Capstans haul and tension the lines that hold ships at docks.
Pulley: A wheel with a grooved rim that guides a rope or cable and changes its direction or mechanical advantage. Both devices guide lines, but a capstan actively drives rope through friction.
Ship's anchor: A device that holds a vessel in place by engaging the seabed or another anchoring surface. Raising heavy anchors was a central historical reason for installing shipboard capstans.
Wrap angle: The angle through which a flexible line contacts a curved surface. More rope contact around the drum generally increases the available frictional grip.
Anchor handling: The deployment, recovery, and movement of anchors and their associated lines or chains. Capstans provide controlled hauling during anchor operations.

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