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Point of sail is a term used to describe a sailing boat's orientation in relation to the wind direction. Except when ''head to wind'', a boat will be on either a port tack or a starboard tack. If the wind is coming from anywhere on the port side, the boat is on port tack. Likewise if the wind is coming from the starboard side, the boat is on starboard tack. For purposes of the International Regulations for Preventing Collisions at Sea and the Racing Rules of Sailing, the wind is assumed to be coming from the side opposite that which the mainsail boom is carried, if the vessel is so rigged. The direction of sail is used for square-rigged vessels. ==No-go zone== Sailboats cannot sail directly into the environmental wind, nor on a course that is too close to the direction from which the wind is blowing. The range of directions into which a boat cannot sail is called the 'no-go zone'. Its width depends on the design of the boat, its rig, and its sails, as well as on the wind strength and the sea state. Depending on the boat and the conditions, the no-go zone may be from 30 to 50 degrees either side of the wind, a 60 to 100 degree area centered on the wind direction. When attempting to sail into the no-go zone, the boat's sails do not produce enough drive to maintain ''way'' or forward momentum through the water. Therefore the boat will eventually coast to a stop, with the rudder becoming less and less effective at controlling the direction of travel. A sailboat's ability to sail close to the wind is referred to as its "pointing" ability. A yacht designed primarily for racing can typically point within 30 or at worst 40 degrees from the wind direction, whereas one designed for cruising may only be able to point within 40 to 50 degrees of the wind direction. Working boats may not be able to point this well and square rigged vessels certainly cannot. The size of the no-go zone varies, but all sailboats have one. A boat turns through the no-go zone as it tacks. Since the boat is passing through the no-go zone, it must maintain momentum until it has turned all the way through this area. If a boat loses steerage way before it exits the no-go zone, it is said to be "in irons" and may stop, return to the original tack, or begin to travel slowly backwards. 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「Point of sail」の詳細全文を読む スポンサード リンク
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