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

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

This calculator finds the theoretical maximum speed of a displacement hull using the standard naval architecture formula: hull speed (knots) = 1.34 × √LWL, where LWL is the vessel's waterline length in feet. Results are shown in both knots and km/h. Displacement vessels — sailboats, trawlers, and full-keel cruisers — are governed by this limit because their hulls cannot easily climb over their own bow wave.

How it works

Enter your vessel's waterline length (LWL) in feet or meters.
The calculator applies the standard formula: hull speed (knots) = 1.34 × √LWL (feet).
Results appear instantly in both knots and km/h.
Use the comparison table to see how different waterline lengths affect theoretical hull speed.

Use cases

Estimate the top cruising speed of a sailboat before purchase.
Compare hull speed potential between different vessel designs.
Plan passage times by knowing the realistic maximum speed.
Understand why longer hulls are faster for displacement boats.
Check if a diesel-powered cruiser can keep pace with your planned route.
Evaluate the speed trade-offs when choosing between two boat lengths.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu