Prop Question

Im thinking about getting a new prop for my 9.9 Yamaha. The aluminum one it came with is pretty dinged up. I would like to get a stainless steel prop, but would also like to get a couple more mph out of the boat. Right now the aluminum prop is 9.25x9 and runs at 5130 rpm with full load, at about 16mph. If I go down a pitch to get the rpms up to around 5300, am I going to loose speed or gain it? Any help would be appreciated.

chrispy186 said:

Im thinking about getting a new prop for my 9.9 Yamaha. The aluminum one it came with is pretty dinged up. I would like to get a stainless steel prop, but would also like to get a couple more mph out of the boat. Right now the aluminum prop is 9.25x9 and runs at 5130 rpm with full load, at about 16mph. If I go down a pitch to get the rpms up to around 5300, am I going to loose speed or gain it? Any help would be appreciated.

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Rule of thumb from a bigger boat, Should gain mph if you dont go into an over rev of the power rating,but ist proly not a whole pitch number. Example I had aluminum went to a stainless same size. Lost 2-300 rpm but same speed. Dinged it up running in low water and even a few small cuts in it. Took it in for repair cut 1/8 inch off dia. and put a small cup on it. RPM was back up along with 3-4 MPH increase. Your gain will be much less with a small power but the only way to know is to try it and make changes if needed.