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Sails are primarily used at sea, on sailing ships as a propulsion system. For purposes of commerce, sails have been largly superceded by other forms of propulsion, such as the internal combustion engine. For recreation, however, sailing vessels remain popular.
The most familiar type of sailboat, a small pleasure yachtA yacht was originally defined as a light, fast sailing vessel used to convey important persons. In later parlance, the definition came to mean any vessel, other than a dinghy, propelled by sail, power or both and used for pleasure cruising and/or yacht r, usually has a sail-planA sail-plan is a formal set of drawings, usually prepared by a marine architect. It shows the various combinations of sail proposed for a sailing ship. The combinations shown in a sail-plan almost always include three configurations: A light air sail plan called a sloopImportant notice ''This article is about the modern civilian boat type. For the warships of the 1800s to World War II, see Sloop-of-war. In sailing, a sloop is a vessel with a single mast on which is hoisted a fore-and-aft mainsail and a single jib, plus. This has two fore-and-aft sails: the mainsailA mainsail is the most important sail raised from the main (or only) mast of a sailing vessel. On a square rigged vessel, it is the lowest and largest sail on the main mast. On a fore-and-aft rigged vessel, it is the lowest and largest and often the only and the jib.
The mainsail extends aftward and is secured the whole length of its edges to the mastA mast is a pole which holds a sail of a boat, see mast (sailing) A mast is also a pole or lattice tower which carries an antenna or aerial. In agriculture, a mast is a crop of fruit or nuts (wild or cultivated) that ripen at the same time. and to a boomThere are several meanings of the word boom a sound such as a sonic boom onomatopoeia the sound of an explosion. a mechanical arm for holding equipment, like a microphone boom (sailing a spar at the foot of a mainsail on a sailing boat. Boom (source port also hung from the mast. The sails of tall ships are attached to wooden timbers or " sparFor the convenience store, see Spar (store). Sailing ships A spar is a round timber or metal pole used on a sailing ship. Masts, booms, gaffs, or yards are all examples of spars. Wooden ships from the age of sail often carried many extra spars of all types"
The jib is secured along its luff to a forestay (strong wire) strung from the top of the mast to the bowsprit on the bow (nose) of the boat.
Fore-and-aft sails can be switched from one side of the boat to the other, in order to alter the boat's course. When the boat's stern crosses the wind, this is called jibing; when the bow crosses the wind, it is called tacking. Tacking repeatedly from port to starboard and/or vice versa, called "beating", is done in order to allow the boat to follow a course into the wind.
A primary feature of a properly designed sail is an amount of " draft", caused by curvature of the surface of the sail. When the sail is oriented into the wind, this curvature induces lift, much like the wing of an airplane. Modern sails are manufactured with a combination of broadseaming and stretchable fabric. The former adds draft, while the latter makes it possible to adjust the draft for different levels of wind.
Other sail powered machines include ice yachts and windmills
Sail construction is governed by the science of aerodynamics.