I just purchased an old 19' 1973 rincon ski boat with a 1974 rude 135 on it. I bought this just to put the motor on my 17' 1993 astro bass boat to get me through the tournament season. The motor came with a 13x19 alum prop on it. With that prop I had a top speed of 40mph GPS at 5000rpm, And it wouldnt get out of the hole without my passenger getting up on the front deck. Yesterday I ran the boat with a 13 3/4x15 prop and it took off like a drag boat and had a top speed of 38mph gps at 5600 rpm. I think I should go with a 17p prop but I dont know what diameter. The 13 3/4x15 was badly damaged. In fact, I had to straighten it with a hammer before we left for the lake. I will be buying a new one of those as well.