Hull speed is the theoretical maximum speed at which a displacement hull can travel efficiently. At this speed, the boat's waterline length equals the distance between the bow and stern waves it creates. Pushing beyond hull speed requires a disproportionate increase in power.

What is the hull speed formula?

Hull speed (knots) = 1.34 × √(LWL in feet). The constant 1.34 comes from the relationship between wave speed and waterline length derived from Froude's wave-making resistance theory. Some sources use 1.34 for displacement hulls and up to 1.55 for very fine hulls.

Can a boat exceed its hull speed?

Yes. Planing hulls rise onto their own bow wave and can travel well above hull speed. Semi-displacement hulls can exceed hull speed with enough power. For classic full-keel sailboats or heavy cruisers, hull speed is a practical upper limit without excessive engine power.

What is the speed-to-length ratio?

The speed-to-length ratio (SLR) is boat speed in knots divided by the square root of LWL in feet. At hull speed the SLR equals 1.34. Below 1.0 the boat is in its most fuel-efficient range; above 1.34 wave-making resistance rises steeply.

Does hull speed apply to catamarans?

The 1.34 formula applies primarily to monohull displacement vessels. Catamarans have slender hulls with lower wave-making resistance and can achieve speed-to-length ratios of 1.5 or higher before resistance climbs sharply.

Hull Speed Calculator

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

Enter your boat's waterline length to instantly calculate its theoretical hull speed in knots, mph, and km/h.

Boat Waterline Length

Enter the waterline length (LWL) of the hull.

Waterline Length (LWL)

Quick Presets

Enter a waterline length to calculate hull speed.

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Summary

Enter your boat's waterline length to instantly calculate its theoretical hull speed in knots, mph, and km/h.

How it works

Enter your boat's waterline length (LWL) in the input field.
Select the unit: feet or meters.
Read the hull speed in knots, miles per hour, and kilometers per hour.
Use the speed-to-length ratio to understand how close your boat is to hull speed at various throttle settings.

Use cases

Estimating the top displacement speed of a sailboat for passage planning.
Comparing hull efficiencies when shopping for a new cruising boat.
Calculating fuel-efficient cruising speed targets for a powerboat.
Teaching naval architecture students the Froude number relationship.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu