How about a 'motorcruiser' powered by a 2.5hp Tohatsu outboard? I met this guy in Antigua and the boat is tiny.

http://www.tohatsu.com/news/seiko.html

The smallest boat to cross the Atlantic is the "Fathers Day" at 5' 4" !!!

some other small boats and voyages
http://www.microcruising.com/famoussmallboats.htm