I think most have missed part of the original question. "how big?" Assuming a sturdy hull, rig, and systems and a skipper that knows what he or she is doing how big is workable - certainly not the 4' boats pictured earlier. It depends what you want to take with you - air conditioning, washer/dryers, electric this and that require a certain size boat - and budget. My minimums are no conversion from sleeping to living like some put up with on a weekender, room to store everything in its place and keep it there, a good galley that works at sea not just tied to the dock, a reliable inboard diesel however small to enter harbor and generate a few amps for convenience, a chart table although this is less critical now than in the past, the ability to load supplies for the intended trip without ruining her sailing abilities which should be good and the ability to stand upright when putting my pants on. In my case 27'.