i have a 20ft. crestliner and i use a 9.9 mercury 4-stroke, it runs great and is nice and quiet and has more than enough power to push my boat at the trolling speeds that i use. even when it's a little rough. i would think that would be sufficient for your pontoon boat. i would also invest in an ez-steer which connects both motors so you can steer it from your steering wheel, hope that helps.