I think an 6 to 10 hp OB would be more than sufficient for a 22ft'er sailing on an inland lake as I assume you'll be doing.
Any motor that checks out OK with a mechanic (compression, cooling pump, etc) should be OK. Don't discard the lesser known motors such as Suzuki, Nissan, Sail, and Yamaha, these 4 are as good as the major Mercury, Envinrude, Johnson, etc. in the smaller HP range.
It is nice if you can get a OB specifically made for a sailboat as they quite often have a alternator output which can charge your on-board battery.
Basically have any motor checked out by a professional, if you want to be sure.
S/V "Sailmates" 1973 IRWIN 32 Classic
I want to live and sail forever, so far so good[/SIGPIC]