Hull Speed Calculator
Updated recently with improved calculation accuracy and expanded examples.
Estimate theoretical hull speed from waterline length using the classic 1.34 × √LWL rule for displacement hulls.
Last updated: August 28, 2026
Author: OceanCalc Editorial Team · Publisher: Albor Digital LLC
Hull Speed Calculator
Result
Approx. hull speed (kn)
7.58
Formula
Hull speed (kn) ≈ 1.34 × √(LWL ft)What is the Hull Speed Calculator?
Estimate theoretical hull speed from waterline length using the classic 1.34 × √LWL rule for displacement hulls.
Based on Froude number ~0.4 for typical monohull wave-making resistance.
hull speed
Hull speed is a practical speed ceiling for many displacement hulls, often approximated from waterline length; it is not a hard physical limit for all vessels.
Related Maritime Calculators
Overview
Hull speed is a practical speed ceiling for many displacement hulls, often approximated from waterline length; it is not a hard physical limit for all vessels. A Hull Speed Calculator is used in maritime navigation to perform precise calculations based on established nautical formulas. This tool allows you to apply your inputs to the stated nautical relationships using accurate and standardized methods.
Key takeaways
- Hull Speed Calculator — Hull speed is a practical speed ceiling for many displacement hulls, often approximated from waterline length; it is not a hard physical limit for all vessels.
- Formula — Classical displacement estimate: V ≈ 1.34√LWL (knots, LWL in feet).
- How to use — Type your figures into the form; outputs refresh so you can compare cases quickly.
How to use
Type your figures into the form; outputs refresh so you can compare cases quickly.
Formula
Core relationship: Hull speed (kn) ≈ 1.34 × √(LWL ft)
Classical displacement estimate: V ≈ 1.34√LWL (knots, LWL in feet). Planing hulls and multihulls often exceed this.
Based on Froude number ~0.4 for typical monohull wave-making resistance.
Practical use cases
Hull Speed Calculator: passage planning, crew briefings, instrument-to-chart unit checks, and verifying mental math when tired or in rough weather.
Tips for accuracy
- Match input units to your chart, GPS, or instrument before trusting the Hull Speed Calculator.
- Cross-check important outputs with a second method or crew when visibility or motion is poor.
- Treat simplified models (waves, radar horizon, etc.) as estimates; real conditions vary.
Practical examples
- 32 ft LWL → ~7.6 kn
- 40 ft → ~8.5 kn
Frequently Asked Questions
Is hull speed a hard limit?
No. It is a useful rule of thumb for displacement monohulls. Light air, surfing, or planing can yield higher speeds.
How accurate is this calculator?
It uses standard maritime formulas and noted approximations. Use it for planning and checks; confirm safety-critical decisions with official sources.
Can I use this on mobile?
Yes. Layouts are responsive for phones and tablets on deck or in the cockpit.
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These calculations are based on standard maritime navigation formulas used in seamanship, chart navigation, and marine route planning.
Results are estimates for educational purposes only and should not be used for real navigation decisions.