Hull speed is the theoretical maximum speed of a displacement vessel before it would need to climb its own bow wave. Beyond this speed, resistance increases dramatically and efficiency drops sharply. It is calculated as 1.34 × √LWL, where LWL is the waterline length in feet.

Why is the constant 1.34?

The 1.34 factor comes from the relationship between wave speed and waterline length. A boat's hull generates waves as it moves; the dominant wave has a length roughly equal to the waterline length. Wave speed (in knots) = 1.34 × √(wave length in feet). Some texts use 1.34–1.35 for displacement hulls.

Can a boat exceed its hull speed?

Yes — light, beamy boats and performance designs can plane or semi-plane above hull speed with sufficient power. However, traditional displacement hulls (heavy keelboats, full-keel sailboats, trawlers) are generally limited by it and consuming far more fuel or sail area to exceed it.

Does this apply to powerboats?

Yes, for displacement or semi-displacement powerboats such as trawler yachts and long-range cruisers. Planing powerboats operate in a different regime and are not constrained by hull speed in the same way.

What is a typical sailboat hull speed?

A 30-foot (9.1 m) waterline sailboat has a hull speed of about 7.3 knots. A 40-foot waterline boat achieves roughly 8.5 knots. Longer racing hulls with 50-foot waterlines approach 9.5 knots.

Displacement Hull Speed Calculator

Name: Displacement Hull Speed Calculator
Availability: InStock
Author: Nham Vu

Enter your vessel's waterline length to get its theoretical maximum hull speed in knots and km/h.

Vessel Waterline Length

Waterline Length (LWL)

Quick Reference

Theoretical hull speeds for common waterline lengths.

LWL (ft)	LWL (m)	Hull Speed (kts)	km/h

Formula: Hull Speed (kts) = 1.34 × √LWL_(ft)
Conversion: 1 knot = 1.852 km/h = 1.151 mph

Summary