I have a 15Hp Yamaha 4 stroke on a 14' aluminum and it hauls butt (25 MPH) with just me in it. Trolls great too.
Now a days you just can't beat a Yamaha. Super easy maintenance also. Last week, I did a complete tune up on it in about two hours. Gotta change the oil often if you troll alot. smile
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Carl C.