Hull Speed Calculator

Calculate the theoretical hull speed of a displacement boat based on waterline length. Understand the speed limit imposed by hull design.

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How It Works

Hull speed = 1.34 x square root of waterline length (in feet). This is the speed at which a displacement hull creates a wave as long as its waterline — pushing faster requires exponentially more power. A 25-foot sailboat has a hull speed of about 6.7 knots. Planing hulls can exceed hull speed by rising on top of their bow wave. Light displacement boats can exceed hull speed by 10-20% without planing. The speed-length ratio (SLR) of 1.34 marks the transition point.