Rik, if you have your own private slip, whatever you can fit in it is what you can put in it. If it sticks out two feet over your yard, that's your business.
If "your" slip is part of a dock-o-minimum or other association, you'll have to consult the deed and association rules. Overhangs may not be allowed.
Offhand I'd expect a "not more than 26-foot-er" with a centerboard or a lifting keel, so it could squeeze into three feet of water. You'd need more than four feet at dead low tide to stick even a typical 24' sailboat in it, so a centerboard or other lifting keel is going to be crticial for you. Unless you're looking for a powerboat.