I have been experimenting with trolling motors and multiple deep-cycle 6 volt batteries to power my O'Day 19 and this spring for my newly acquired Catalina Capri 22 WK. The quietness goes along with the quietness of sailing.
http://groups.yahoo.com/group/electricboats/
The Yahoo group on electric boats is a wonderful source of experiments from simple trolling motors to large multi-hull yachts with generators.
Just remember that there are many different solutions because there are many different goals that the owners have.
For myself, a simple 12 Minn Kota Endura is sufficient for maneuvering around the dock and reasonably quiet water. Four (4) supplied all of the energy I needed for last July 4th week on Lake Champlain. It is good for about 3 mph. I am investigating RE-E-Power (
http://www.re-e-power.com/) for 2010 (budgetary reasons).
John