Boat Speed Calculator

Your details

Crouch's formula estimates top speed for planing hulls. Prop mode calculates from engine RPM and propeller geometry. Hull speed is the theoretical limit for displacement hulls.
Shaft horsepower delivered to the propeller shaft. For outboards this is usually 85-90 % of rated engine hp.
hp
The total weight of the loaded boat in pounds, equal to the weight of water it displaces (Archimedes' principle).
lb
Selects the Crouch constant (C). Heavier displacement boats use lower C values; racing hulls use higher ones.
Estimated top speedPlaning speed
43.9

Calculated boat speed in your chosen unit

Speed (mph)43.9
Speed (knots)38.2
Speed (km/h)70.7
Crouch's constant (C)150
43.9 mph
Displacement<10Semi-planing10-25Planing25-50High-speed50-80Racing80+

Estimated speed: 43.9 mph

  • Crouch's constant of 150 is used for this boat type. Upgrading to the next class raises C by 40-60 points.
  • Power-to-weight ratio: 0.0857 hp/lb. Reducing displacement or adding horsepower both increase speed.

Next stepThis is a theoretical top-speed estimate. Real-world speed varies with hull condition, loading, sea state, and prop efficiency. Try the Propeller RPM mode for a pitch-based check.

 = Powered by OnlyCalculators