I had a Yamaha 9.9hp four stroke high thrust on the back of my 222. It did the job and will get you home (just not very quick). I believe my max speed with the engine was around 6.5 knots.
9.9 HP is probably just fine. I use a 15 HP Honda on a G/W 228, and about 1/2 throttle is all I ever use. Any more and the boat just starts to "squat" and push more water-doesn't go any faster. I also max out a little over 6 knots.