Work out engine power for boat speed instantly with clear inputs, formula shown and shareable results.
The Admiralty coefficient method sizes power from displacement and speed: power scales with displacement to the two-thirds power times speed cubed, divided by a coefficient that depends on the speed-length ratio. It captures the sharp rise in resistance as a displacement hull approaches hull speed.
Admiralty coefficient
SHP = (displacement^(2/3) x V^3) / C, with C set by the speed-length ratio
Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.
Wave-making resistance grows very rapidly once the hull's own wave system is as long as the hull, so the coefficient C drops and power demand climbs.
No. Once planing, dynamic lift changes the physics and Savitsky-type methods should be used instead.