If you're only interested in casual trips out on the lake or down the local river for a few hours, this could be a worthy consideration.
No smoke, no noise, no pollution, well sort of, something has to recharge the batteries though as the article states you could use wind and or solar to extend your range!
Anyway it's interesting to look at and contemplate.
http://www.sillette.co.uk/elect_saildrives.pdf