Sail

A sail derives power from the wind to provide motive power for sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and sail-powered land vehicles. Sails mobilize lift and drag properties as air passes along the surface, functioning similarly to a wing in a vertical orientation. In most cases sails are supported directly by a mast rigidly attached to the sailing craft or on a wire stay attached to the mast, however some craft employ a flexible mount for a mast. Sails also employ spars and battens to help determine their shape, aligned with airflow. As a result, sails come in a variety of shapes that include both triangular and quadrilateral configurations, usually with curved edges that promote three-dimensional curvature of the sail.

Kites also power , but do not employ a mast to support the airfoil and are beyond the scope of this article.

Sailing craft employ two types of rig, the square rig and the fore-and-aft rig.

The square rig carries the primary driving sails are carried on horizontal spars, which are perpendicular or , to the keel of the vessel and to the masts. These spars are called yards and their tips, beyond the last stay, are called the yardarms. A ship mainly so rigged is called a square-rigger. The square rig is aerodynamically most efficient when running (sailing downwind).

A fore-and-aft rig consists of sails that are set along the line of the keel rather than perpendicular to it. Vessels so rigged are described as fore-and-aft rigged.

Archaeological studies of the Cucuteni-Trypillian culture ceramics show use of sailing boats from the sixth millennium onwards. Excavations of the Ubaid period (c. 6000 -4300 BC) in Mesopotamia provides direct evidence of sailing boats.

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