well i have a 15 pitch prop aluminum im thinking of purchasing a stainless steal do you know of a good brand prop i can purcgase were i can get the same rpm or a bit more and if possible gain some speed ???
I looked up gear ratio it should be 1.85:1 and at 4500RPM that would be approx 34.5 mph, slippage accounts for the amount less than max theoretical that you measured. 4500 is the min WOT and 5500 is max WOT operating range for that motor.
To get higher rpms from prop change would mean less pitch. It is doubtful that you would get the 1K rpms to hit max WOT range from a 13P. I think you'd pickup little less than 500 rpm's from the 13P and you would lose couple mph's.
I do not think you are going to get more speed. Unless the motor is under performing or the boat is heavier than it should be. Sounds like 15P is the right pitch to get max speed out of that motor/boat combo.
ok guys i went today and bought some things for the boat fuel filter, oil, waterpump kit (not instaled). i cranked my motor up to run it for a while and notice im only running on two cylinders one of my coils are bad so i think thats whats causing my 4500 rpm problem !!!!