Originally Posted by greenleaf
Could any 1 tell me what i should do propwise?
Put the 15 back on.....5500rpm at wide open throttle sounds about right, and 34 knots for that engine on that boat seems about right.
check the rpm range for your engine, or the band where the power is developed.
My thinking on this is if your rpm range is say 5000-5500 then for normal use you want to achieve 5500rpm with just one person on board and a full tank of fuel, that way as you load the boat up you come down into the "powerband"
If you carry lots of gear all the time you may want to achieve 5000rpm with all the gear on board and sacrifice the top speed unloaded in favour of loaded performance.
In short as cookee says you have run out of power with the 15" so theres no point going up a pitch, if you want to go faster get more power!