I have a 1973 Forester Opsrey 164 (16'4" long and is basicly like a baja of hydrostream type lo-profile boat) and I currently have a 13 1/2"x17" aluminum prop on it and I was only getting getting 38 mph out of it. I did not have a tach at the time so I can not say what the 1975 Johnson 115 was running at. I now ordered the parts to make my johnon a 140hp with boysen reeds as well. I want a prop to just get top speed out of becouse I can still use the 17 for slolom skiing. I was think a 3 blade 13 1/2x24 SS prop. Would that be to much? I also just bought a 96 rinker race boat with a 55 johnson that is from the same era as my 115. Would the props be interchangable? Thanks a lot guys and the more info the better. Zach