Windsurfing
Technique
In planing conditions a harness is typically worn to more efficiently use the rider's weight to counter the force in the sail. As the wind increases, the rider continues to sheet the sail, the fin generates more lift, and the board gains speed, transitioning onto a plane. The volume of board in the water (displacement) decreases, and the rider moves rearward, stepping into the footstraps for improved control. When planing, the board skims on the surface rather than displacing water as it moves. Planing can be achieved at different wind speeds depending on the rider's weight, sail and fin size, wave conditions, and rider ability. With modern equipment planing can normally be achieved at a wind speed of around 12 kn (6 m/s). The transition from displacement motion to planing requires a jump in energy, but once planing, water resistance decreases dramatically. This means that it is possible to continue to plane, although the wind has dropped below a level that would be required to transition to plane. A board in plane can be much smaller than a board moving by displacement (thereby gaining an advantage in gear weight and board control). Lateral resistance to the wind is provided by the fin alone (generating more lift at higher speeds) and a centreboard is no longer used (smaller boards do not have one). A fin generates lift, transferring a strong load to the board, and so is usually constructed of carbon fiber for accurate shape and strength. A low-pressure area develops on the windward side of the fin, which can lead to cavitation, leading to a sudden loss of lift, called "spin-out" (equivalent to "stalling" in flight terminology). Ideal planing conditions for most recreational riders is 15–25 kn (7.7–13 m/s) of wind, but experts can windsurf in much windier conditions. Planing is considered one of the most exhilarating aspects of the sport.
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