Originally Posted by wellhouse
i'm using a yamaha 13 x 19 ali prop and it goes straight to 6000rpm and i feel it is under propped. you don't get much extra speed between 5000-6000rpm?
Well you didn't say you had anything at all before...
Since you feel its underpropped why don't you try a 13x21"? Assuming the exact same load, that should drop you to 5600-5700rpm WOT. I would not expect much more speed with the 21", maybe 40kn. Once you have a starting point its all trial and error after that.