I just tried my new Yamaha F150 yesterday with a 13 3/4 X 19 SS prop (left over fm my old 200 hp), and it maxed out at 5600rpms. Its on a 19' Grady '91, total package with two people and full tank about 3300 lbs. My goal is higher top end instead of better hole shot. Should I try a 13 3/4 X 17 or a 14 1/4 X 18. I don't quite understand how the diameter of the prop can alter the rpms.