Have a Johnson 55 hp outboard. I had the propeller come off and became lost. I got a second hand one 13 spline 11 3/4 x 17 right hand propeller. Went out and I don't go anywhere motor screams rpm but the boat would be travelling at a slow walking pace. In reverse we go quicker. It sounds like it cavitates when you try to rev it. It dosnt make sense and no one seems to know any help or ideas would be welcomed and appreciated.