[Chas911]

IMHO, my experience with more than a few boats is that you will be fine with a V6 up to about 19'. More than fine actually, V6s work great in lighter boats and will be the most fuel efficient. If you start going up in length, the 21 footers can start to get fairly heavy and you will probably want at least a 350. 21 footers usually have quite a bit more room in them but are also a little harder to get on and off the trailer and back around. Not a lot of difference but you need to determine what fits your needs.