Yamaha two stroke 25 with a small minn-kota for trolling. put the fuel and batteries in the bow. Any 8 hp or bigger outboard will not go slow enough for me on a 16 foot aluminum so you might as well get the 25. If you are set on trolling with the gas motor, I would only consider a Honda or Yamaha four stroke probably 5 or 8 horse.
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The drift is always greener on the other side.