Calculating Hull Speed

This article presents a calculator for assisting in determining the hull speed potential of a moderate speed propeller driven planing hull, based on the hull's weight, the horsepower, and a "hull factor." The hull factor is a constant which is used to convert the necessary dimension of weight and power into a convenient speed unit.

Crouch's Formula

Naval architect George Crouch proposed that a useful estimate of the speed of a moderate planing hull could be derived from the boat's weight and horsepower. If the weight is given in pounds and the power is given in horsepower, the hull factor will be a range of 150 to 250 and the speed will be calculated in miles per hour. The variables are related by

MPH = [  ( HP / LBS )^0.5 ] x C

where C = a constant that depends on the hull form.

Crouch proposed that C would have a value for various hull types as follows

PLANING HULL SPEED CONSTANTS--MPH

C      Hull Type

172    Average runabout, cruiser, passenger vessel
218    High-speed runabout, very light high-speed cruiser
240    Race boat types
253    Three-point hydroplanes, stepped hydroplanes
265    Racing power catamarans and sea sleds

The Calculator

Hull Speed Calculator by James F. and James W. Hebert.
INPUTS CALCULATED
Weight Power Hull Factor Boat Speed
 LBS  HP     MPH
After Crouch's Formula

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Copyright © 1999, 2000 by James W. Hebert. Unauthorized reproduction prohibited!

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Author: James W. Hebert
This article first appeared April 16, 2006.