I have a 19 foot lund with a 9.9 merc.4 stroke at top speed it's at 5.5mph but can still move me in high waves.That what you need to conceder if your big motor breaks down will it get you home in all kinds of weather If it's a high profile boat you might want to go with a higher HP motor.But the choice is up to you.I hope this helps.Good luck.
Question, why is the guy selling it, what did he have it on and was it too small or too heavy, does it vibrate to much or is it too noisy? Sometimes a good deal is for the one selling it. Another thing you may want to consider is does it have the capacity to charge your system while trolling? A day on the water can discharge your boat battery if you have minimal toys, fish finder, radio, gps, electric down riggers or an old battery. The last thing you want to do is sink good money into a problem that will only cost you more to get out of. Best of luck:)
hes buying a 21 foot dory for rowing and doesnt want the motor on it. i said i might want the motor and we could maybe make a deal after he buys it. didnt consider the charging problem and that would definately play into things. if i can get a good deal on it i may get it anyways for one of the smaller rowboats i have. been wanting to get something together thats easier to tow and launch in the smaller ponds. thanks for the info, its definatly a bartering point. whatever happens i would need to put an offer in quickly as i would want a motor on that dorey if i bought it for rowing