Sports

Instant, private, and free

Hull Speed Calculator.

Estimate displacement-hull speed using the explicit 1.34-knots convention and waterline length.

On-device calculationNo signup
01

Set your values

Results update as you type.

Waterline length (ft): 32.808399

Waterline length (ft)

0.000000
Hull speed (knots): 7.675335

Hull speed (knots)

0.000000
Hull speed (km/h): 14.21472

Hull speed (km/h)

0.000000
Hull speed (m/s): 3.948533

Hull speed (m/s)

0.000000

Results update automatically as you type.

Use Cases

Boat Performance Planning

Determine the theoretical maximum speed of your displacement-hull boat to plan trips and estimate travel times.

Example: A 10-meter sailboat has a hull speed of about 7.7 knots.

Design and Comparison

Compare different boats' hull speeds based on waterline length to understand their performance potential.

Example: Compare a 12m trawler vs a 15m trawler.

Frequently Asked Questions

What is hull speed?
Hull speed is the theoretical maximum speed of a displacement hull, determined by its waterline length. It's calculated as 1.34 times the square root of the waterline length in feet, or 2.43 times the square root in meters. This calculator uses the standard formula.
How is hull speed calculated?
The calculator uses the formula: hull speed (in knots) = 1.34 * sqrt(waterline length in feet). Since you input length in meters, it first converts to feet, then applies the formula. The result is an estimate of the maximum efficient speed.
Why is hull speed important?
Hull speed indicates the speed at which a displacement hull becomes inefficient, as it starts to create large waves. Exceeding hull speed requires significantly more power. Knowing it helps with trip planning and fuel efficiency.

Tips & Common Mistakes

Tips

  • Measure the waterline length accurately from the waterline at the bow to the waterline at the stern.
  • Remember that hull speed is a theoretical limit; actual speed depends on hull shape, displacement, and power.
  • Use this calculator for planning fuel consumption and estimating arrival times on long passages.
  • For planning hulls (e.g., catamarans), this formula does not apply; they can exceed hull speed.

Common Mistakes to Avoid

  • Using overall length instead of waterline length, which overestimates hull speed.
  • Assuming the boat will always reach hull speed; it depends on power and conditions.
  • Forgetting that the formula is for displacement hulls, not planing hulls.

Last updated: August 13, 2026