15 hp four strike prop issues??

[Nadinayammy]

Hey there...
I have a 5 yr. old 15 hp four stoke yammy outboard. Very low miles, runs excellent. I use it on a 14 foot alum. Lund boat. Since new this engine has had very, very littletop end speed. My 9.9's are faster.
My stock prop is. 91/4 inchx11inch. J1 or "L".
I think maybe a higher thrust prop is what I need? If I can find one?
THanks?

[boscoe99]

What is the wide open throttle RPM with the boat loaded?

You need a propeller that will let that motor turn at or near 6000 RPM when the boat is loaded. Go down in propeller pitch as necessary. You might need to go to an 8 pitch Yamaha propeller.

I would not expect an F15 to get a 14' aluminum boat on plane with any load in the boat. I had a 25 HP two stroke on mine and was always sorry I did not go with the 35 HP model.

[Nadinayammy]

THanks and sorry for late reply to your comments.
I dont know the rpm when running full out, loaded but the engine sounds like it is low rpm.
Yes. This engine is small for the 14 foot boat.
Still trying to understand prop pitch vs, speed and power. Is there any rule like....the higher the pitch rating the more top end power.??
Much appreciated.

[boscoe99]

Less pitch generally means more power. In the old days they referred to props as power props and speed props.

But there is the issue that the motor needs to get up to about 5500 RPM to create its maximum power. If the propeller has too much pitch it might not get to the point where the power is made.

[Nadinayammy]

Thanks. Sounds like a prop with less pitch than my 11 pitch would be worth a try...along with a tach test. Maybe an 8 pitch...Now, just to find that prop!!!