I know a few guys around here run the boats, but you might have better luck checking boat-specific forums (I know Offshore Electrics is popular, those guys build some mean machines).
I think you will find there is more to it than just hull, prop, and driveshaft. You need a rudder and steering system and other misc. running hardware, waterproof radio box, watercooled motor and ESC, guys who know about boats could no doubt list more things you'll need.
You might be better off just picking up one of these (either the velocity mono or velocity cat) if you want to try out a brushless electric boat:
http://www.minicatracingusa.com/
I've been thinking about trying one for awhile, someone else here got the mono I think and it looks pretty slick. Seems like a decent price, you would probably spend more trying to put something together with the brushless gear you already have, since it isn't boat or water-cooled specific gear.