Originally Posted by roland.fisher
also not sure what WOT means, but we get about 50 on rpm meter (5,000 rpm I think)
WOT = Wide Open Throttle - basically you choose the correct prop by making sure the WOT engine revs are in the right range, and while I don't know Yamahas, 5000rpm at WOT sounds a bit low to me - what does the book say for this engine?
As DHD says you may need a finer pitch prop which will give you more revs at any given engine RPM, possibly a higher top speed and definitely more oomph off the mark which is what you want if hauling somebody out of the water especially if they're a bit of a pie shifter.
Is your 38mph actually "mph" or is it knots (nautical mph) - I would have thought 38mph (33kt) is a bit on the slow side as my 5.8 Humber with 115hp would just touch 40kt (46mph) lightly loaded, which might also suggest your engine is overpropped.
Edited to add I've just looked and WOT range for the F115 engine is 5000 to 6000rpm so you could easily drop a couple of inches in pitch, as long as the engine doesn't exceed 6000rpm at WOT you will be fine