Hull Speed Calculator
Hull Speed
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In km/h
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Speed/Length Ratio
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Understanding Hull Speed
Hull speed = 1.34 x sqrt(waterline length in feet). At this speed, bow and stern waves merge into one hull-length wave.
A 30-ft boat has hull speed ~7.3 knots. A 60-ft vessel: ~10.4 knots. Longer hulls are inherently faster.
Planing hulls exceed hull speed by rising on their bow wave. Displacement hulls face extreme resistance above hull speed.
Frequently Asked Questions
Hull speed formula?
Speed (knots) = 1.34 x sqrt(LWL feet). Based on wave speed and wavelength relationship.
Can boats exceed hull speed?
Planing hulls can. Light displacement by 10-20%. Heavy displacement faces enormous resistance.
Why does waterline length matter?
Longer waterlines create longer waves, and longer waves travel faster. Wave speed proportional to sqrt(wavelength).
Speed/length ratio?
SLR = Speed / sqrt(LWL). At 1.34, you are at hull speed. Below 1.0 is comfortable cruising.