Re: Estimating speed
Engine RPM divided by lower unit gear ratio, multiplied by prop pitch, divide by 12, divide by 88. Yeilds theoretical speed in MPH.
Then subtract 10% for estimated prop slip.
Even so, this is theoretical and a given hull may not approach that speed. It will, however, tell you if you are way out of whack or if you are overestimating the capability of your engine.
Example: expecting 50 MPH at 5500 RPM with a 17 pitch prop and 2 to 1 gearcase is expecting more than the prop/engine can deliver. 40 MPH would be a more realistic expectation.
