The major downside is that there is no good way to "fill the tank" on an electric vehicle unless you have access to a really high current charger. Unlikely on a lake anytime soon.

Any vehicle where you use less than about a tank of gas worth a day electric makes sense, like commuting in an electric car for most people you can very easily be charged back up over night.
If you have access to a very high current charger, basically a Tesla supercharger, then it's getting pretty compareable (not quite there, but pretty compareable) to just filling a gas tank.

But if you can't charge over night or have a handy high (and I mean HIGH) current charger available, then it doesn't really work.

This is what I concluded after renting a Tesla for a week on a recent vacation. Sweet car though.