Evinrude 115hp Prop Help

[Traxion]

I have a 1995 Evinrude 115 mounted on a 1992 Sea Nymph 17.5' aluminum deep V. Boat is stern heavy with kicker and batteries. I've ran a 17p Stiletto Advantage 1, I am getting around 5100 RPM with a speed of 37-38 mph. Overall grip with this prop sucks, blowout occurs at pretty shallow trim angles, and I get porpising at pretty low trim levels. Holeshot is OK. I just tried out a 15p Powertech RAF, I got around 5100 RPM with a speed of 34.5 mph. Overall grip was great, loved the attitude of the boat, holeshot and grip were good. Just way slow.

I'm just not sure what I have to do to gain RPM's. I expected to gain more RPM going to the 15p Powertech, but I really gained nothing. I know the Powertech is a more agressive prop than the Stiletto but I really expected an RPM gain. I really am not happy with the speed of the Powertech, but I love the grip. Any suggestions here?

 

[skibrain]

Re: Evinrude 115hp Prop Help

Have you checked the mounting height of the motor? (vertical position on transom)
If too low that could explain low rpm (extra drag of too much lower unit in the water) however too low would not be consistent with prop blowout. GEnerally the cavitation plate should be close to the bottom of the V of the hull.

 

[Traxion]

Re: Evinrude 115hp Prop Help

Motor height is about 1" above keel. Low as it will go. I don't think height is an issue because blowout with the 17p is pretty serious. Any more height and it would be terrible IMO.

 

[Fed]

Re: Evinrude 115hp Prop Help

Because your WOT RPMs didn't increase when you dropped back to a 15" prop I'd be checking the following.

1) Are the carby butterflys fully open at WOT.
You may be able to check this by looking at the roll pins on the outside of the carbys.

2) Is your WOT timing correct, you may need a full link & sync.

If you intent to the the work yourself then a genuine OMC manual for your exact motor is invaluable.