Hull Speed

An approximate speed at which wave-making resistance rises sharply for a conventional displacement hull.

As speed increases, a displacement vessel creates a longer bow-and-stern wave system. Near the traditional hull-speed region, the wavelength approaches the vessel’s waterline length and substantially more power is normally required for a further increase.

A commonly quoted estimate in knots is 1.34 times the square root of waterline length in feet, but the coefficient and behaviour vary with hull form, displacement and conditions. Hull speed is not an absolute maximum: slender displacement hulls can exceed the estimate and planing or foiling craft operate by different principles.