RPM Range for F115

[Speedboater]

I have a 2003 F115TXRB motor and trying to find the right prop. i currently have a Yamaha 131/2 X 15-K aluminum prop on the boat and at WOT rpm is 6200-6300 without any trim. what is the correct RPM range for this motor.
Thanks
Todd

[boscoe99]

6000 RPM when the throttle is wide open, with the boat loaded, with the motor trimmed up only to the point of most efficiency, on a hot and humid summer day.

[panasonic]

Mr Boscoe, what rpm does the Rev limiter cut in on that engine? I would think 6300 would be getting close?

[Speedboater]

It was a hot day (im located in Florida) with 1/2 tank of gas and two adults. the boat is a 1997 Wellcraft 19' center console. i recently purchased the boat and the prop on it when i purchased it was a turning point hustler 13.25 x 17. at WOT with this prop it was around 5100 and the boat struggled to get on plane. the Yamaha 15p prop feels much better and no problem getting on plane. im just concerned it is a little too small and letting the motor rev too high.

[boscoe99]

It was a hot day (im located in Florida) with 1/2 tank of gas and two adults. the boat is a 1997 Wellcraft 19' center console. i recently purchased the boat and the prop on it when i purchased it was a turning point hustler 13.25 x 17. at WOT with this prop it was around 5100 and the boat struggled to get on plane. the Yamaha 15p prop feels much better and no problem getting on plane. im just concerned it is a little too small and letting the motor rev too high.

It is your job to not let the engine overspeed if and when there is a time that it can do so.

[boscoe99]

Mr Boscoe, what rpm does the Rev limiter cut in on that engine? I would think 6300 would be getting close?

6200 is the published number.

[DennisG01]

How did it perform on the test ride? Did the previous owner use the trim better than you are, maybe?

5100 vs 6300 RPM is NOT even close to being due to simply a change of 2" of pitch. That would only account for a couple hundred-ish RPM's. There's more going on - either user error, dirty bottom or mechanical issue (including, but not limited to, an error in the tach... although that's probably on the rare side of things).

[99yam40]

was the 1st prop SS and a 3 blade??
the new one is not only 2" less pitch it is also 1/4" bigger.
I agree it should not have made that big of a difference

But SS props usually have more cup or double cupped and are thinner blades

different styles of props/blades can make a difference also

[Speedboater]

Ok i kind of thought the same thing with that much of a change in RPM with only going from a 17 to a 15p.
Both props are aluminum
the 17 looks to be new and is more of a cupped looking blade
the 15 is a used prop i purchased on ebay. and is more of a clever looking blade.

is it possible it is the style blade that makes this much difference? and there is always the possibility the ebay prop has been altered. i may be better off purchasing a new 15p to test just hate to spend the money jjust to find out.

thanks
Todd

[DennisG01]

I don't see any way that, regardless of the type of prop, 2" of pitch is going to account for that much of a difference. Actually, it's probably even more than the 1200 RPM I talked about above. If the 5100 you got with the 17" was likely trimmed up to get max MPH/RPM and, as you stated, the 15" was 6300 WITHOUT any trim... once you trim the engine up, you're going to gain even more RPM on top of the 6300. Something isn't adding up - see my thoughts on that above - I wouldn't waste any money on another prop until you address those other issues.

[99yam40]

here is a performance bulletin for a 18' Wellcraft to look at and compare .
https://yamahaoutboards.com/en-us/ho...2017-05-17_occ

from looking at those stats, I would think the prop you got off e bay has been modified.
might see if a prop shop could have a look at it to see what has been done to it.

might ask around to see is a shop would let you test a prop or 2 if you buy one from them

[Speedboater]

Thanks for all the info guys, I don’t believe there is anything wrong with the boat, hull, motor, trim, ect. I believe it is all with the props. and with the info from the link for the 18’ Wellcraft (basically the same boat, mine has a 1’ pulpit making it an 18’ boat and is 150lb heavier) the results using a 15p prop are only a little off. (I have included the info below). The props (15 P) do look a little different. The newer Wellcraft is using a more rounded eared prop (Talon) and mine is more of a cleaver look. (see the pics below) not sure what is going on with the 17P but at this point im thinking it is not a true 17P. I will be taking the props to a local shop and see what they can find out. Thanks again for your help guys!

Newer Wellcraft with 115 Yamaha and 13 ½ x 15P prop
6100 RPM = 37.8 MPH
4000 RPM = 21.9 MPH

My Wellcraft 115 Yamaha and 13 ½ x 15P prop
6200 RPM 35 MPH
4000 PPM 18 MPH

[99yam40]

only problem with that is you said you did not trim the motor at all.
might try trimming it properly to see what speed you get at the RPMs they listed

good thought of the original 17 being modified instead of the 15