Re-proping questions

7lazy77 · Aug 9, 2011

I have a 1994 24' pontoon with a 1994 Johnson 115 hp motor that I just purchased & hauled home. I live in Wyoming & 6300' higher in elevation from where I purchased the pontoon. On my first trip out, I was only able to go about 15 mph & seemed to be lacking the "umph". Spoke with my local dealer & he said that I should start with re-proping the motor with less pitch. Just wanted to get some extra information from the fellow forum members before I do this. Mostly use the pontoon for fishing & cruising, but also like to pull the kids around on a tube too.
I believe the motor has a 16 pitch propeller now (will have to pull it to varify), should I reduce that down to 13 pitch?
Should I get a 3 or 4 blade prop? What are the advantages/disadvantages of each?
What are the differences between steel & aluminum props? Any advantages/disadvanges of each?

steelespike · Aug 9, 2011

Re: Re-proping questions

I believe there is a 3% reduction in power for each 1000 ft of elevatioon.
So your down about 18% Best way to select a prop is based on the present wot rpm and speed.A 1" change in pitch will result in "about" 200 rpm change.You'll need the present size to know where to start.If you don't have the rpm specs selecting a prop is like putting a gun to the motors power head.Besides being bad for the motor it may deliver poor performance and economy.

SparkieBoat · Aug 9, 2011

Re: Re-proping questions

a 13 pitch prop is a common pitch for pontoons.

7lazy77 · Aug 10, 2011

Re: Re-proping questions

Pulled the prop last night & it says 13 1/2 x 13 prop. Should I consider going with an 11 prop?

Leardriver · Aug 10, 2011

Re: Re-proping questions

Yes, or even lower. If you take a standard I/O from sea level, and it ran a 21 pitch there, you would need a 17 or even 15 pitch at your altitude. A change of around 25-30% pitch is needed, to compensate for the same loss in horsepower that occurs at altitude.

If there is such thing as a 10 pitch, it would give you closer to the same proportional change. Otherwise, an 11 pitch would be a great step in the right direction.

7lazy77 · Aug 10, 2011

Re: Re-proping questions

Thanks for the input fellers. Before I spend the money & "guess" on the pitch, I think I will take the the others advice to take the toon out & run it WOT & get the rpm & speed. I will post back with my findings & hopefully I can narrow down the best prop for my pontoon.

SparkieBoat · Aug 10, 2011

Re: Re-proping questions

considering you may be down 20HP because of the altitude ...I still think the 13 P should push it to mid 5k RPMs, I had an 85 on the back of a 28' toon once and it wound out nicely. maybe you have some engine troubles. you need to check your RPMs at wOT. the 85 would push my 28' toon over 20 MPH.

7lazy77 · Aug 14, 2011

Re: Re-proping questions

Had a chance to take the pontoon out. At WOT it was running at 5100 rpm's @ 19 mph. Knowing this, should I consider a 11 pitch prop or a 9 pitch?

steelespike · Aug 15, 2011

Re: Re-proping questions

I would do an 11" prop should put you at 5400-5500.
If you run lightly loaded most of the time the 13 may work.

7lazy77 · Aug 15, 2011

Re: Re-proping questions

Most of the time, I have a heavy load.....me & my family (5 total) & we usually have some friends riding along (5 more) plus all the gear, food & drinks. So if I have 4 adults & 6 kids (all under 9 years old), will an 11 pitch prop still work or should I consider the 9 pitch??? THANKS

sethjon · Aug 28, 2011

Re: Re-proping questions

7lazy77 said:
Had a chance to take the pontoon out. At WOT it was running at 5100 rpm's @ 19 mph. Knowing this, should I consider a 11 pitch prop or a 9 pitch?

The small difference is not worth the time or money. It would also be a little more stressful to the motor. Sounds like right now you have a good set up.

SparkieBoat · Aug 28, 2011

Re: Re-proping questions

you could also try raising your motor up 1 or 2 holes, this will help a lot if it does not cavitate. I still think you should check your fuel pump, spark, compression and link and sync.. even loaded and high altitude a 115 should turn a 13p prop into the mid 5K RPMs, you are not far off ..but a little IMO...

Re-proping questions

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