What prop to use

F

flyboyray

Recruit
Joined
Jun 27, 2011
Messages
3
I have a 22 foot Sweetwater pontoon with a 2007 90 horse evinrude e-tech. It has a 13.5 x 15 aluminum prop and runs maybe 20-21 mph (as per the gps). Max rpm is about 4700-4800. I'd like to get a little more speed by changing the prop. I have to check my prop p/n to see whether it is a cupped or un-cupped prop. E-tech book says it should run about halfway between the normal range of 4500-5500. I'd like to raise the rpm's by maybe 500. Would maybe a 13.5 by 13 prop help? By the way, all numbers in this message are with 1 person aboard and clean (not polished) pontoons. I use a/c coil cleaner to clean them.
 
Silvertip

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,762
Re: What prop to use

A 13P prop will raise rpm but understand that speed does not necessarily go up as well. The prop is the transmission on a boat and it only has one gear. Therefore dropping pitch is like shifting down in your car. If you hold the gas pedal steady and shift down one gear, engine rpm goes up but speed doesn't change. If the engine was lugging severely then you might see an increase as the drop in pitch puts the engine on its power curve and can not gather additional rpm and thus more speed. In your case, the 13P may help in that regard since the engine is lugging. You should also ensure the throttle is opening fully (at the engine).
 
F

flyboyray

Recruit
Joined
Jun 27, 2011
Messages
3
Re: What prop to use

Thanks for the help Silvertip. I understand fully. The engine is not lugging at all. It's just not getting up to or near max rpm. I've checked the throttle and it's good. I'm a retired aircraft mechanic for almost 50 years so I kind of know what I'm doing, just don't know much about marine stuff. From what I've read, dropping the pitch from 15 to 13 should give me about 200 to 300 more rpm's. Do you agree with that? If you agree, I will try it and see what happens. Thanks again.
 
You must log in or register to reply here.
Top