Originally Posted by Hydro Junkie

Electrics are something I don't know that much about. You might try contacting Offshore Electrics, tell them what you have for a boat, along with its weight and tell them what electronics you already have. They should be able to point you in the right direction.
With that said, the guys that race 1/8 scale electric scale hydroplanes run 8S packs and 830-860 KV motors. You have to remember, you're pushing more weight through a denser medium and spinning higher RPM so it's going to take more power in both the batteries and motors to get the results you want
Offshore Electrics address is at this link: RC Boats by Offshore Electrics