speed-to-length ratio

ship design

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July 14, 2026

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The speed-length ratio is a key concept in ship design, calculated by dividing a ship's speed in knots by the square root of its length in feet. This ratio is crucial for understanding a ship's hydrodynamics and the power required for propulsion.12

The resistance a ship encounters moving through water has several components, including friction and wave-making resistance. Wave-making resistance increases significantly with speed. For conventional ships, operating at a speed-to-length ratio higher than approximately 1.3 is practically impossible due to the immense power needed to overcome the generated wave system. Naval architects use this ratio to select hull forms that minimize resistance at efficient operating speeds.34

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Design of the hull
…impossible to operate at a speed-to-length ratio (speed in nautical miles per hour, divided by the square root of the waterline length in feet) higher than approximately 1.3. Beyond that realm even a trivial increase in speed requires a virtually infinite increase in power in order to fulfill the energy…
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…impossible to operate at a speed-to-length ratio (speed in nautical miles per hour, divided by the square root of the waterline length in feet) higher than approximately 1.3. Beyond that realm even a trivial increase in speed requires a virtually infinite increase in power in order to fulfill the energy…
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