Here is my latest project:
http://www.youtube.com/watch?v=gD-7VVxMGxgIt's an 8 horse evinrude converted to electric. It is pretty much equal to the performance of the gas motor on 60 volts, although it has much better acceleration. The converted motor is actually lighter than the original gas motor because the electric part only weighs about 20lbs. The motor is a briggs and stratton etek motor , which can sustain about 5 kw continuous (8hp ish) and provide about 15 kw peak (I only draw about 5kw peak due to the small prop). If propped differently this motor could easily put out 10hp or more. Battery life and battery weight would be your only issue. I can troll for probably 10 hours straight on 2 deep cycle batteries, but planing requires much more power. In the video I had 60 volts of rc lithium batteries from hobby city (only 8 pounds worth!). If you figure you can plane on 5kw if you want it to last an hour you'd need about 5kwh of energy which in rc batteries would weigh about 70-80lbs. Wouldn't be cheap though....I'm saving up for some lithiums for my home built electric car.