Need help with prop

[kmcburnett]

I have a 1993 JC Pontoon Suntoon 24ft. It has a 1977 Evinrude 85 hp. The motor runs well and has a 14x13 aluminum prop. At WOT I am only turning 4600 rpm. While it runs good this seems low to me. Is this acceptable for rpm's? If not what recommendations do you have for the prop?
Also this motor has a hydrofoil on it. The boat is nothing more than a floating brick so I see no need for this as it always stays on plane. Could this be hurting it?
Thanks for all your help

 

[steelespike]

Re: Need help with prop

The foil may be there it help limit ventilation It might cost a couple of mph and some rpm dragging in the water.
Wouldn't hurt to try it without the foil.
An 11 or 13 would be normal for that setup.It would be better if we had the speed at 4600.A gps is best and some cells have a gps app.Rpm and gps speed help to evaluate the performance.Also will help us tell if the tach is accurate.
Motor is rated for 4500-5500 While acceptable 4600 doesn't leave much room for added weight and the motor would be happier
over 5000. If the prop is from 77 just replacing it with new could improve performance.

 

[Mi duckdown]

Re: Need help with prop

As Steele posted. remove hydrafoil and post with results.

 

[kmcburnett]

Re: Need help with prop

I have raised the motor one hole and removed the hydrofoil. The prop on the boat is a new one (14x13). I plan on taking it to the lake this weekend and will post with results using my gps/speedometer on my phone. Thanks for everyones help

 

[steelespike]

Re: Need help with prop

Usually recommend doing one change at a time.If you get some kind of screwy result you don't know if its from raising it or removing the foil. But give her a test. Probably won't be a problem.

 

[kmcburnett]

Re: Need help with prop

Quick Update - I raised the motor two holes, which was the max, totaling approximately 1 inch of lift and removed the foil. I put the boat in the water on Sunday with not one change in performance. The boat still ran good with max rpm of 4600. I did not use the gps as I forgot about it but plan on going back out this week at which time I will see the actual speed. I was also thinking about trying to adjust the throttle cable and see if that could help. Ill keep you posted.

 

[steelespike]

Re: Need help with prop

It wouldn't hurt check that the throttle advances all the way.
Also would be good to get us the speed before final prop selection.