Need help with prop.

[Milan15]

I have a 07 28ft Tritoon with a Mercury 115 4 stroke outboard. The WOT should be 6,200 rpm. I can only get 5,000 rpm at wide open throttle. The propeller is a 11 pitch. I tried a 13 pitch with the same results. Is there anything I can do to get the 6,200 rpm?
Thank You

 

[ThomW]

Being off by almost 1200 RPM's doesn't seem like a prop pitch fix, especially if you are already running an 11. What are you using to gauge your RPM's? Dash panels can be faulty or wrong.
As a general rule, each inch you DROP your pitch, you gain about 200 RPM's. So going from an 11 to 13 should actually lower your max RPM's, not raise them.
It could be a motor issue, and not a prop issue. Maybe the motor needs a good tune up...or maybe the 28 foot tri-toon is just too much boat for the 115hp to push out any more than the 5000 you are getting.??

 

[Milan15]

Being off by almost 1200 RPM's doesn't seem like a prop pitch fix, especially if you are already running an 11. What are you using to gauge your RPM's? Dash panels can be faulty or wrong.
As a general rule, each inch you DROP your pitch, you gain about 200 RPM's. So going from an 11 to 13 should actually lower your max RPM's, not raise them.
It could be a motor issue, and not a prop issue. Maybe the motor needs a good tune up...or maybe the 28 foot tri-toon is just too much boat for the 115hp to push out any more than the 5000 you are getting.??

So originally when I bought the boat last year it had a 10 pitch. I could get 6200 rpm however towing a tube going into a corner it would ventilate really bad. So I called Precision Prop in Spokane and they said I need a 13 pitch. Thats when the rpm went down to 5000rpm. I then went to Mercury Prop Selector and based on all the info of the boat and motor it said I need a 11 pitch cupped. Bought that and still the same 5000 rpm.

 

[ThomW]

What type of prop was the original 10? What about the new 11? Did you keep the diameter the same? Going up 1 inch in pitch should not cause a 1200 drop in RPM's...something is not right.

 

[Milan15]

Both 3 blade 13 inch diameter. I'm confused on why I would lose that much rpm.

 

[ThomW]

Have you tried putting the old 10 back on to see if you can still get the 6200?

 

[Milan15]

Have you tried putting the old 10 back on to see if you can still get the 6200?

No not yet. Will do that next.

 

[ThomW]

I mean...if you go back to the 10 and are still getting 5000...then I think something else has come up during the testing of props...if it goes back up to 6200...then I am baffled on what prop you would need to find your happy median.

 

[Thirsty Endgrain]

Does that engine not seem small for a 28' to anyone else? I know basically nothing about toons though...