Help with prop selection

[jayace77]

Hi, I've got a 1994 17.5 foot Century fish and ski. It has a 94 Yamaha 115tlrs on it with a 13X17 prop. My problem is at WOT I'm only at about 4300 RPM and according to GPS about 43 MPH and I should be at 5500RPM at WOT, now I don't think this is the original prop for the boat and the engine runs perfect so no RPM lost from poor running. Just need help reaching my WOT and possibly getting more speed out of it, I don't tow skiers so out of the hole isn't a concern. Is going with a 4 blade an option? Also I know if you drop the pitch you will gain RPM but I'm not sure where to go, or if I should go with a smaller diameter prop. Thanks for any help....

 

[steelespike]

Re: Help with prop selection

I suspect your tach is not accurate it may be set wrong or defective.
Your speed is about right rpm is way low.An 11" prop would be required to get you to about 5,500 rpm. If tach has a selector switch check where
it is set rotate it back and forth to clean the contacts see if it helps.
You may be able to borrow a shop tach to check against yours.But you will find your tach is off.

 

[Home Cookin']

Re: Help with prop selection

It's also possible you're running lean and not getting all the fuel at WOT that you used to. Lots of things in the fuel path come with age and cause this. Simple test is to get someone to pump the ball while driving to see if it increases your RPMs.

 

[jayace77]

Re: Help with prop selection

Guess it could be a bad tach setting, I'll try that this weekend. Would that setting only cause in issue with my WOT reading cause it seems ok at idle and low RPM. Don't think it's the fuel, I did try the primer bulb trick and no change....Thanks

 

[tawood]

Re: Help with prop selection

BTW, a 4 blade would probably lower your wot rpm even more. (It did for my boat, which is what I was looking for).
Tim