Prop Diamter vs RPM question

[Tom Smyth]

Currentlyspinning a 3 blade small ear CHopper 22 inch pitch about 5K. Like the way it hooks up and pulls, but rpm no where near what i want for WOT. The chopper is a 14 inch diamter. What would reducing the diamter to 13.5 inches do regarding RPM and Preformance?

Thanks

[Carter Powell]

What type of boat, motor, etc are you running. It will help to know. Dropping a half inch in diameter may increase the rpm 5-600 rpm but it may also cost you in the slippage department. If your boat has a hard time getting on plane now it will make it much worse with a smaller diameter prop. More information will really help.

Best wishes, Carter Powell

[Tom Smyth]

Sorry. In line merc 6 on a 400 lb vee bottom. running tall gear ratios at 1.78 to 1. Looking for 5800-6K for WOT.

[Carter Powell]

I would definately say a 14" diameter prop is too much for an inline six to swing. I think with your gearing there are a couple of things to try. First, with that light of a boat I think you could take the blades down to about 13.25 in diameter. If that does not get it done then you are probably going to have to drop down in pitch a bit. 20" maybe. It will be much cheaper to cut down the diameter first.

Best wishes, Carter Powell

[Tom Smyth]

that is what i was thinking, the diameter is too much for the engine. Not sure how much reducing diamter will do to perfromance vs gaining rpm. So far everytime i drop some pitch , i pick up equal amounts of rpm and MPH. At some point the diamter has to come into play though.