My advice to DerbyDan, and anyone else looking to convert/upgrade their boat, is to understand how 'very' different the electrics operate when running boats compared to cars;
When you 'gun' the throttle in a car, the slipper will absorb the power or you'll spin the wheels. In a boat you don't have a slipper, and the prop will not spin free in the water; it will grip (hard) and cause your motor to pull huge amps. It will get hot very quickly and fry your motor/ESC/batts.
If you want to really get into the boat scene then you'll find that getting the 'set-up' right is the most important bit. Props come in many different shapes and sizes and materials and they will all load up the electronics in different ways. Honestly, the whole thing can get very complex, and very very expensive.
If you want to upgrade an RTR boat or convert one to electric, then my advice would be to use the complete electrics from an existing boat that has been tried and tested.
Derbydan, for that boat I would recommend something like the SV27, Stilletto or UL-1 electrics. All of the components are readily available from various hobbystores. but I would also spend a bit of time scanning a decent forum such as OffshoreElectrics.com
You'll need to keep and eye on the propshaft and use a decent marine grade grease. If you want longivity from the upgrade, I'd advise you to change that as well. If you want the simple route, then just add a decent brushed esc, with a hotter brushed motor and a decent bttery pack. You should also buy a simple water cooling coil, which wraps around the motor and allows you to run water through it to cool the motor.
Honestly, you have lots of options, but I would scan the OffshoreElectrics forum first to gain a bit more knowledge, and also to allow you to consider all of your options.
Hope that helps!
