Prop Research

[rcnight]

I recently posted a question about prop selection for my 20 and received a good response-thanks. However, was wondering what difference does the diameter play in performance? Also, what effect does every +/- degree in pitch have on your WOT? Was just wondering???

[bigblockdock]

RC, Prop pitch is measured in inches and represents how far the prop will push the boat forward with each revolution of the prop without figuring in any slippage. ( most props have 5 to 15% slippage.) Each inch of pitch is worth around 200 to 300 RPM's. The motor needs to be able to turn the manufactures recommended rpm's at wot. Too low of a wot rpm will shorten the engines life. Bigger/heavier boats need bigger dia. props for pushing power/control. Diameter will also effect engine rpm but at a lesser degree. Bigger dia. props take more power to turn and can also give a boat more lift in the stern/bow depending on the design of the prop. If you have a 19 inch pitch prop with a 14 inch diameter and are turning 5200 at wot and the motor needs 5600 to be right you can drop down to a 17 " pitch/14 " dia. and be in the right area but if you went to a 17" pitch /13 1/2 dia. you may be over 5600 rpm at wot.. I think that's how it works that is without figuring in prop "rake" and "cup". Hope this helps. Butch