Sailing is the propulsion of a vehicle and the control of its movement with large (usually fabric) foils called sails. By changing the rigging, rudder, and sometimes the keel or centre board, a sailor manages the force of the wind on the sails in order to move the vessel relative to its surrounding medium (typically water, but also land and ice) and change its direction and speed. Mastery of the skill requires experience in varying wind and sea conditions, as well as knowledge concerning sailboats themselves and a keen understanding of one's surroundings.
While there are still some places in the world where sail-powered passenger, fishing and trading vessels are used, these craft have become rarer as internal combustion engines have become economically viable in even the poorest and most remote areas. In most countries sailing is enjoyed as a recreational activity or as a sport. Recreational sailing or yachting can be divided into racing and cruising. Cruising can include extended offshore and ocean-crossing trips, coastal sailing within sight of land, and daysailing.
Throughout history sailing has been instrumental in the development of civilization, affording mankind greater mobility than travel over land, whether for trade, transport or warfare, and the capacity for fishing. The earliest representation of a ship under sail appears on a painted disc found in Kuwait dating to the late 5th millennium BC.[1] Advances in sailing technology from the Middle Ages onward enabled Arab, Chinese, Indian and European explorers to make longer voyages into regions with extreme weather and climatic conditions. There were improvements in sails, masts and rigging; navigation equipment improved. From the 15th century onwards, European ships went further north, stayed longer on the Grand Banks and in the Gulf of St. Lawrence, and eventually began to explore the Pacific Northwest and the Western Arctic.[2] Sailing has contributed to many great explorations in the world.
The air interacting with the sails of a sailing vessel creates various forces, including reaction forces. If the sails are properly oriented with respect to the wind, then the net force on the sails will move the vessel forward. However, boats propelled by sails cannot sail directly into the wind. They must tack (turn the boat through the eye of the wind) back and forth in order to progress directly upwind (see below Beating or "Working"). A sail works exactly like the wing of an airplane. The wind flow over the surface of the sail creates a force perpendicular to the mean surface of the sail; a third of this force applies to the intrados, two-thirds apply to the extrados. The longitudinal componant of that force pulls the boat forward, the transversal one causes the boat to list
Sails are airfoils that work by using an airflow set up by the wind and the motion of the boat.[3][4][5] Sails work in two "modes" to use the wind to generate force (see Forces on sails):
The wind that a boat experiences is the combination of the true wind (i.e. the wind relative to a stationary object) and the wind that occurs due to the forward motion of the boat. This combination is the apparent wind, which is the relative velocity of the wind relative to the boat.
When sailing upwind the apparent wind is greater than the true wind and the direction of the apparent wind will be forward of the true wind. Some high-performance boats are capable of traveling faster than the true windspeed on some points of sail, see for example the Hydroptère, which set a world speed record in 2009 by sailing 1.71 times the speed of the wind.[6][7] Iceboats can typically sail at 5 times the speed of the wind.[8]
Source: Wikipedia
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