Sailboat Hull Speed Calculator
Estimate the hull speed of a displacement sailboat from its waterline length, then compare a planned speed using the speed-length ratio and Froude number.
Hull speed by waterline length
| Waterline length | In feet | Hull speed |
|---|
Hull speed is estimated as v = 1.34·√LWL with LWL in feet, which is about 2.43·√LWL in metres, in knots. The coefficient comes from a Froude number near 0.40, where a displacement hull's wave-making resistance climbs steeply; it is a practical planning speed, not a hard physical limit. Waterline length, displacement and hull shape all matter: slender or light hulls, multihulls and planing hulls exceed this figure, while heavy full-bodied hulls may reach it only in flat water. The speed-length ratio is v(kn)/√LWL(ft) and the Froude number is v/√(g·LWL) with g = 9.80665 m/s². Everything runs locally in your browser.