Quote from: Ron Hill on July 14, 2023, 05:08:07 PMThis has been discussed before when I selected my Flexofold prop. I suggest that the original poster go back and look at my explanation why our more powerful MkII M35B engines should actually have a lower pitch prop than your smaller engine. https://c34.org/bbs/index.php/topic,10205.msg78626.html#msg78626
ban : you should be able to up the pitch to 10" without any problem!!
The M35B engines were paired with a transmission that has a more aggressive gear ratio, so the prop spins 15% faster at a given engine RPM, which loads down the engine more, requiring lower pitch. In addition to that, the Flexofold has a blade design that generates more thrust at a given RPM than other props, which further increases the load on the engine. In my case, my maximum RPM went from 3400 with the Michigan Sailer 15x9 to 3100 with the Flexofold 15x9, hard evidence that the Flexofold pitch should be 15x9. John Langford had a 15x10 Flexofold on his MkII and reported problems with it requiring it to be adjusted back to 15x9. (Check the link for the quote.) Bottom line: The MkII boats are a different powertrain, and the Flexofold also loads down the engine more than other props of equivalent pitch.
If original poster chooses Flexofold 3-blade, I'd recommend 15x9. But he's welcome to do whatever he wants, and the pitch setting on his current prop could also help guide his decision.