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Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-trough dimension (height) increases as well. When hull speed is exceeded, a vessel in displacement mode ...
A velocity prediction program (VPP) is a computer program which solves for the performance of a sailing yacht in various wind conditions by balancing hull and sail forces. VPPs are used by yacht designers, boat builders, model testers, sailors, sailmakers, also America's Cup teams, to predict the performance of a sailboat before it has been built or prior to major modifications.
In particular, any "displacement" or non-planing boat requires much greater power to accelerate beyond its hull speed, which is determined by the length of the waterline, and can be calculated using the formula: Vmax (in knots) = square root of LWL (in feet) x 1.34. The hull speed is the speed at which the wavelength of the bow wave stretches ...
For the International rule, the rating number is approximately equal to the sailing length of the hull. These boats have long overhangs which allow the waterline length to increase as the boat heels over. A displacement hull's maximum speed (the hull speed) is directly proportional to the square root of its waterline length. [2] The first ...
The CCA characterizes the formula as "rough". A lower value is supposed to indicate a sailboat is less likely to capsize. A value of 2 is taken as a cutoff for acceptable to certain race committees. However this is an arbitrary cutoff based on the performance of boats in the 1979 Fastnet race. The CSF does not consider the hull shape or ballast ...
In recent years ultrasonic speed sensors have become available. These use two ultrasonic transducers—one forward, one aft—that send ultrasonic pulses through the water flowing past the hull. By calculating the time differential in pulse propagation from one sensor to the other, the device calculates the speed of the hull through the water.
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Royal Navy World War II motor torpedo boat planing at speed on calm water showing its hard chine hull - note how most of the forepart of the boat is out of the water. At rest, a vessel's weight is borne entirely by the buoyant force. Every hull acts as a displacement hull at low speeds: the buoyant force is mainly responsible for supporting the ...