Is this good enough?

[Barry63052]

OK, I have a 1991 Evinrude pushing a 1991 18' bass buggy pontoon. At WOT I'm getting 4800 rpm's at about 17 mph. The prop on there no is a little chewed up. Not real bad, but its there. I am thinking about getting a new prop. Should I stay with one like I got now? Or try to get a little bit more rpm's out of it?

 

[Scott Danforth]

Re: Is this good enough?

since your on a pontoon, I would start first by adjusting motor height. Many pontoons have the motor way too deep.

 

[Barry63052]

Re: Is this good enough?

OK, I will start there then. Is there any rules or tried and true tricks for finding the right height? Or is it all one big guessing game?

 

[steelespike]

Re: Is this good enough?

If your not having any ventilation(cavitation) You may be able to raise it a little.Start with 2 holes and check the results.
Pontoon "setup" Varies widely.
What year and hp? What prop size?Usually near the base of the blades or under the prop nut.
We need the wot Rpm and gps speed.Some cells have a gps app.

 

[Barry63052]

Re: Is this good enough?

Ok, Im back. Sorry it took so long. I was having problems with the tach so I ordered a tiny tach for it. But anyway, here is the results:
1991 40HP evinrude motor
1991 18' Bass Buggy pontoon
WOT rpm is about 1480 to 5000
Top speed is 17 mph (according to gps phone app and original speedometer)
Prop says 12+1/2 X 13
Three blade prop

 

[steelespike]

Re: Is this good enough?

I think you have a little too much prop. At 4800 you need about 700 rpm more.
I think a 11" prop should put you at about 5200. May improve your slip numbers
and possibly your speed though that may be a wash.
Do you have any trouble with ventilation/cavitation?

 

[Barry63052]

Re: Is this good enough?

No, no problems with that at all. Or at least not that I know of!

 

[Scott Danforth]

Re: Is this good enough?

before changing props, I would recommend raising the motor until you start to have ventilation problems. Then drop it down a hole. If you are running too deep, it hurts performance.

Then once you get motor height dialed in, then take WOT RPM and speed readings to then dial in your prop.

 

[steelespike]

Re: Is this good enough?

If you don't have any ventilation issues you may be able to raise the motor as suggested.
If it is excessively low raising it could improve performance.

 

[Barry63052]

Re: Is this good enough?

Ok, cool. I will give that a shot this weekend.