Hi Everyone, So I have a 16' Sylvan Backtroller Aluminum fishing boat, pushed by a tiller model 1981 Evinrude 25 HP long shaft motor. When I bought the boat, the included prop was very badly damaged and needs replacement. I did test run the boat with the banged up prop however, and noticed that at about 3/4 throttle, the prop begins to cavitate, resulting in higher rpm and no gains in speed. I am concerned as to whether or not the current prop size is appropriate for the boat, and whether or not a pitch change is in order. The current prop is a 9 1/2 x 10. Is this cavitation a result of just a very banged up prop, possibly improper pitch, or possibly a spun hub (it has been cold so I cant do the normal run test to see if it is spun). I am buying a new prop regardless, but need to know the diameter and pitch to buy. Also, the cavitation plate on the motor sits just at the bottom of the transom, so I don't think a height adjustment is in order to fix the problem. Thanks in advance for your opinions and help.
