yamaha f-115 prop help please

[pine island fred]

Opinion suggest I might be overproped causing my new F-115 to make oil. Try to give the particulars. 18 ft. ctr cnsl. mfg by RIVIERA fiber corp. Hull is quite similar to a boston whaler. Load is always limited to 34 gal. of gas, one battery, 2 people, cooler and safety equip. Boat stays on plane at 2800 rpm some times I will push it up to 3400. Right now the engine maxes out at 5200.
Suggestions please! Would like to get it right the first time. Would reducing down to a 15 in pitch on a stainless prop be to much? Is there an average for increased rpm per reduction in pitch? thanks fred

 

[Crownie2]

Re: yamaha f-115 prop help please

Fred - generally, each inch in pitch reduction will increase RPM's by about 100.

 

[pine island fred]

Re: yamaha f-115 prop help please

Thankyou for the reply. Looks like I have a big pitch reduction ahead of me. fred

 

[troypolla]

Re: yamaha f-115 prop help please

I have a Yam F115 on a Keywest 19ft cc. At WOT my rpm is about 5700. I have a SS 15inch prop. Powertech is the brand.

Fred. What is your top speed at WOT. mine is only 34-35 at 5700-5800. between 5200 and WOT my speed does not increase more than 1-2 mph. just curious what pitch prop you have now, trim tabs etc.
Thanks
Troy

 

[Dhadley]

Re: yamaha f-115 prop help please

Work on fixing the non-seating rings. If you don't get that issue resolved you may be looking at a powerhead replacement. Bearings don't last long in diluted oil. Babying the motor is killing it.

Try raising the motor to gain rpm. Keep changing the oil until you get the rings seated.