Cruising area: South and east coasts. Eastbourne Marina.
Join Date: Mar 2006
Location: Uckfield, East Sussex.
Posts: 758
Engine RPM divided by gear ratio times prop. pitch divided by 12 (inches in a foot) divided by 5280 (feet in a mile) times 60 = Optimum Possible Top Speed (100%). 87-89% is very good. This is from Powerboat Magazine - believe it if you will.
or go here and go to bottom of screen on to prop slip calculator and enter you pitch gear ratio and rpm and click calculate under speed and it will tell you your speed