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A spinnaker is a special type of sail that is designed specifically for sailing off the wind from a reaching course to a downwind, i.e. with the wind 90°–180° off bow. The spinnaker fills with wind and balloons out in front of the boat when it is deployed, called ''flying''. It is constructed of lightweight fabric, usually nylon, and is often brightly coloured. It may be optimised for a particular range of wind angles, as either a reaching or a running spinnaker, by the shaping of the panels and seams. Some types of spinnaker can be carried by the side of the boat, but still in front of the mast. This is called "flying a shy spinnaker", and is used for reaching. The spinnaker is often called a ''kite'', or a ''chute'' (as in cruising chute) because it somewhat resembles a parachute in both construction and appearance. This should not be confused with the spinnaker chute which is a hull fitting sometimes used for launching and recovering the spinnaker. A purported etymology has the first boat to carry this sail being a Cowes yacht named ''Sphinx'', from which "Sphinx's Acre" and eventually "Spinnaker". ==Operation== A spinnaker is used for sailing with the direction of the wind. Symmetrical spinnakers have large amounts of camber, making them nearly hemispherical. Both lift and drag propel the boat forward when moving with the wind. Reaching spinnakers have less camber as they operate within an airflow that generates lift. A well designed spinnaker will have taut leading edges when filled; leading edges that curl in will both reduce the lift and risk a collapse of the spinnaker. A well designed spinnaker will also have a smooth curve when filled, with no bubbles or depressions caused by inconsistent stretching of the sail fabric. Any deviations from a smooth curve will cause the airflow over the leeward side of the sail to separate causing a reduction in lift and reduced performance. When running downwind in heavy weather or when hit by a gust, with or without a spinnaker, there may be a tendency for a roll of increasing amplitude to build up, known as the death roll. It has been shown that this is due to aerodynamic instability of bermuda rigs when running, which can be aggravated by gusts, waves, mainsail twist, daggerboard etc. too far down, hull form, and the sailing equivalent of pilot-induced oscillation. Excessive heel leads to loss of rudder effectiveness resulting in the boat slewing round uncontrollably in the direction opposite to the direction of heel. This is known as broaching. Aerodynamic instability when running can be countered by easing the pole forward slightly and over-sheeting the spinnaker somewhat to stop it swinging from side to side, by reducing mainsail twist using the boom vang, and by skillfully trimming the mainsheet. Luffing carefully onto a broad reach may help to retain control, as can moving everyone's weight as far aft as possible. Reducing sail should be considered. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spinnaker」の詳細全文を読む スポンサード リンク
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