Hull Speed Calculator
Enter your boat's waterline length to estimate its theoretical hull speed, the natural speed limit of a displacement hull, in knots, mph and km/h.
How to calculate hull speed
- Measure your boat's waterline length (LWL) in feet.
- Enter the waterline length below.
- Read off the theoretical hull speed in knots, mph and km/h.
Examples
A 25 ft waterline sailboat
waterlineLengthFt = 25
6.7 knots (about 7.71 mph or 12.41 km/h)
Frequently asked questions
What is hull speed?
Hull speed is the theoretical top speed of a displacement hull, set by the wave it makes. As speed rises the bow and stern waves stretch until they match the hull length and the boat sits in its own trough.
What is the hull speed formula?
The classic formula is speed in knots equals 1.34 times the square root of the waterline length in feet. Longer waterlines give higher hull speeds.
Can a boat go faster than its hull speed?
Yes. Light planing hulls and multihulls climb over their bow wave and exceed it. Heavy displacement hulls need a lot more power for small gains beyond hull speed.
Should I use waterline length or overall length?
Use waterline length (LWL), not length overall (LOA). Only the part of the hull in the water makes the wave that sets the speed limit.
Why do some sources use a different coefficient?
The 1.34 coefficient is the traditional value. Some naval architects use 1.1 to 1.5 depending on hull shape, so treat the result as an estimate, not a hard limit.
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