James,
In your search for electric propulsion have you come across a generator/motor combination- one that you would use as a outboard to get into a slip, and a generator while cruising? I ask because I am currently designing one- and plan on marketing it if there is a need.
I already do the same thing with bikes (veloutah.com)
You might find some of these experiences worth studying:
Electric Drive ProjectMore on Electric Boat PropulsionBoth threads include various links to motor and batt sources, etc.
Moving a cruising boat with electric requires a TON of juice; 48V-60V motors seem to be the 'norm' for these kinds of projects, and that means BIG battery banks even with low amp-hour storage capacity.