OceanCalc

Hull Speed Calculator — Meters

Estimate theoretical hull speed from waterline length using the classic 1.34 × √LWL rule for displacement hulls.

Last updated: March 28, 2026

Author: OceanCalc Editorial Team · Publisher: Albor Digital LLC

Page focus

When you want meter-centric outputs from the Hull Speed Calculator, work in the fields above and cross-check against metric charts or soundings.

Hull Speed Calculator

Result

Approx. hull speed (kn)

7.58

Formula

Hull speed (kn) ≈ 1.34 × √(LWL ft)

Overview

The Hull Speed Calculator gives you precise nautical results from familiar formulas, with an interface suited to deck and chart-table use.

How to use

With the Hull Speed Calculator, type your figures into the inputs above—the output refreshes live, making it easy to sanity-check several cases.

Formula

The relationship behind this tool is: 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

Typical uses for the Hull Speed Calculator include passage planning, briefing crew, converting instrument readouts to chart units, and double-checking mental math when fatigue or weather make errors more likely.

Tips for accuracy

  • Confirm that the units you enter match your chart, GPS, or instrument readout before relying on the Hull Speed Calculator.
  • In rough weather or poor visibility, cross-check important results with a second method or a crew member.
  • Treat simplified models (wave height, radar horizon, etc.) as estimates—real conditions vary with fetch, refraction, and equipment.

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?

    This calculator uses standard maritime formulas and practical approximations where noted. It is suitable for planning and cross-checks; always verify safety-critical decisions with official references and local conditions.

  • Can I use this on mobile?

    Yes. OceanCalc tools are responsive and work on phones and tablets for quick checks on deck or in the cockpit.

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Results are estimates for educational purposes only and should not be used for real navigation decisions.

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