Hull Speed Calculator for Boats

Hull Speed Calculator

This Hull Speed Calculator finds the theoretical maximum efficient speed of a displacement hull from its waterline length. Enter length in feet or meters to get hull speed in knots, mph, and km/h. You can also work backward from a target speed to find the required waterline length. Compare with our Boat Speed Calculator.

The Hull Speed Formula

Displacement hull speed in knots is v = 1.34 × √L, where L is waterline length in feet. In metric form, hull speed in km/h is approximately 2.43 × √L with L in meters. Beyond hull speed, a boat must climb its bow wave, which wastes power and limits efficient cruising.

When Hull Speed Matters

Hull speed is most useful for sailboats and displacement powerboats with traditional hull shapes. Long, narrow hulls and planing designs can exceed this limit without the same penalty. Loading a boat heavier lengthens the waterline slightly, which can raise theoretical hull speed.

Frequently Asked Questions

What is hull speed?

Hull speed is the speed at which a displacement hull's bow wave wavelength equals the waterline length. It represents the practical upper limit for efficient cruising on many traditional boat designs.

How do I calculate hull speed?

Multiply 1.34 by the square root of waterline length in feet. For a 36-foot waterline, hull speed is about 8.04 knots.

Can a boat go faster than hull speed?

Yes, but it requires significantly more power. The hull starts to plane or push through its bow wave, which is inefficient for displacement designs.

What is waterline length?

Waterline length (LWL) is the length of the hull where it meets the water surface when the boat is loaded normally. It is shorter than overall boat length.

Does hull speed apply to all boats?

No. Planing hulls, catamarans, and slender racing designs can exceed classical hull speed limits. The formula is a guideline for conventional displacement monohulls.

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Hull Speed Calculator