Originally Posted by shahid
While we're waiting for some of the experts to respond, I can help you with the dimensions question.
The first figure is the diameter of the propeller itself (end to end) which is fairly straight forward to measure.
The second is the pitch (19", 21"). Measurement of the pitch will take a bit of doing of course not required in your case. Basically the pitch is the theoretical distance the propeller would travel in one complete revolution. Think of it as a screw and imagine the distance the screw would move in one complete turn - that's your pitch.
What RPMs are your engines running at WOT? is it within the recommended rev band of the manufacturer? If yes, then which side of the spectrum is it towards?
Basically, switching to a prop with a higher pitch would reduce the RPMs and conversely for a prop with a lower pitch.
OK thanks, that makes sence, i guessed it was something on those lines. max rated rpm is 5600, on medium load the engines reach the max very easily. from wot u say on pitch and diameter then my different props r going to have the same affect which i have proven with trial, looks like i might need a 14 x 21 or simillar. obviously this will be an experts decision, i will contact ho yamaha here in egypt but they r a bit backward on tech stuff...cheers