Sails

A sail is a fabric or composite surface that uses wind to propel a boat. Mounted on a mast and often a boom, a sail converts wind energy into forward thrust and lift. Sail trim and the point of sail determine speed and steering, aided by the hull and rudder.

Early sails were made of canvas or linen. Modern sails use synthetic fabrics such as Dacron, Kevlar, or carbon fiber, often in panels with battens to hold shape. The sail's leading edge is the luff, the trailing edge the leech, and the bottom edge the foot; reefs reduce area in strong winds.

Common types include square sails on traditional ships; Bermuda rig fore-and-aft sails (triangular mainsail and jib) on most yachts; gaff rigs, lateen rigs, lug sails, and junk rigs. Fore-and-aft sails include the mainsail and fore-sail; downwind sails such as spinnakers or gennakers provide extra power when sailing with the wind.

Rigging configurations include sloop (one mast, two sails), cutter, ketch, yawl, and schooner. Sails are controlled by halyards to raise them and sheets to trim them. The boom supports the lower edge of the mainsail; reefs and partial sail areas reduce handling loads in heavy wind.

Sails have ancient origins in Egypt and Mesopotamia and evolved through Mediterranean and Atlantic trade routes. In the modern era, sail design emphasizes efficiency, ease of handling, and safety, with racing and cruising boats using advanced materials and shape optimization.