Zodiac/Avon 285/310 required engine sizes
I have a Zodiak 310 with the HP floor and keel. I went with an 8hp 2cyl 4-stroke Honda. With two people, the thing FLIES!!! (Probably could pull a water skier!!!) A little scary with just one person, if you hit the throttle too hard, you could flip! The Honda is the max weight (90lbs) the boat can handle, if you went with a 2-stroke, you could go to 10hp, but I decided against that for environmental reasons.
There are folks who would go less power, thinking the size of my motor is overkill. However, it is nice to have the "punch" needed to cary 4 people, and gear, back to the boat after the wind and waves pick up! I have seen dingy''s with smaller motors have to wait out a 20kt breeze to get back to the mother ship.
The HP floor and keel are great as well. The whole thing rolls up into it''s carry bag and weighs in at about 70lbs or so.