Transport Factor—How You Get It

By George L. Petrie

More of this Feature • Part 1: Wrap-Up • Part 2: Wrap-Up continued • Transport Factor
Related Resources • Boat Test Index

Transport Factor = Weight x (Speed x 1.689) / (Power x 550)
   Speed and Power figures here are multiplied by the constants described below, to free the Transport Factor from dimensional concerns.

Weight. For each yacht, we took the builder’s figure for dry weight in pounds, to which we added the weights of fuel, water, persons, and gear onboard during our test, as reported in each PMY boat test article.

Speed. Top speed in knots, as measured on test day, based on a two-way average measured with a Stalker radar gun. Multiply by 1.689 to convert from knots to feet-per-second, the units required by the formula.

Power. Maximum rated horsepower of the engines installed on the test boat, as per the engine manufacturer’s specifications. Multiply by 550 to convert from hp to foot-pounds-per-second, the units required by the formula.

Speed-Length Ratio. Top speed, in knots, divided by the square root of the yacht’s at-rest waterline length in feet. —G.L.P.

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