Thread: Need Prop Advice; SeaArk 2072 mv with Yamaha F115LB

Not exactly, but I have a Yamaha C115 2 stroke and settled on a stainless power pro prop. A 19P gives me around 5600 RPMs before blowing out. I have an 18'6" Xpress that I added a lot of weight to. It holds the bow up well. Prior to it I tried bought a stainless Laser II prop. It worked very well but didn't give me quite enough bow lift. That prop is in excellent condition and was checked by a prop shop in Huntsville. I had a better hole shot with the Laser II. If you're interested in it, I'd take $200 TYD.

Yamaha sends a lot of their motors to the dealers without a prop. Oftentimes, it is up to the dealer to select a prop to put on the motor and marry it with the boat. More times than not, many of them don't seem to get it right.

I have some experience with that exact motor as my dad has it on his boat and his boat, in my opinion, was NOT up to par. I have the same hull in my boat and I noticed a huge difference.

If memory serves me, his boat came with a 13x15 and had similar issues. Don't quote me, but I beleive I went to an SS 13.75x17 on his boat. Now I am right in the RPM range while increaseing top end. The holeshot was also greatly improved as the motor was underpropped and seemed to "Spin out". Keep in mind that his was an aluminum one from the factory and I switched it out with SS.

With Pitch, the lower the pitch, the greater increase in RPM (about 200RPM per 1 inch of pit). Raise the pitch and you will lower the RPM.
With Diameter, you increase the diameter on a slower boat and decrease it on a faster boat. Look in your book for RPM range but, if memory serves me 5800 at WOT is what you should shoot for. 6000 would proably be ideal. So, based on what you said, I would go UP to a 17P and probably up to a 13.75 diameter. Raising up to 17 should decrease you by around 400rpm, increasing the diameter should acount for some of the speed you lost when you lowered the RPM.

Hope that helps.

Put the 17 pitch Yamaha SST on yesterday, and it was a lot better overall. Still planed out at 18-20 mph.
Cruises nicely around 4k rpm doing 30 mph.
Full throttle gave me 46 mph at 6200 rpm. Apparently the limit is 6300 for this engine, so I'm close to it, but not dangerously close.
If I run across a 19 pitch it would be interesting to try, but honestly I don't want to go any faster.
The 17 pitch is going to be better when we load all of our duck hunting stuff in this winter too.