What size or how many mAh

[Buoyhunter]

Hey guys I have a 31" ML Hydro. Planning on running it in a p limited race. setup for 4S with a mild prop. how many mAh am I going to need to complete the heats? I want to balance the boat out properly too...

[CraigP]

Need more info... What's your motor and prop?

[Buoyhunter]

Its a ProBoat stock 1050 kV motor and a ABC 1817

[CraigP]

I run a 1050kv on 8s. That would be real slow on 4s... you want to shoot for about 36,000 to 38,000RPM. So your motor would be closer to a 2500kv for competition and 2200kv for sport boating. You'll get lapped twice running that slow a motor! Most people are running 7000-10,000mah packs, running 4s2p packs. Hydros like some weight up front.

[Buoyhunter]

Craig, are you a NAMBA or IMPBA member? IMPBA has a voltage cap at 16.92 V for P class hulls. So I guess what you're saying is i need to up the kV?

[CraigP]

I'm not a member, but I'm really good with the electrical components... the reason I don't race is because it is centered around low voltage setups. That drives amps up, and amps is what breaks parts. But let's get back to your project... So with a 4s, 14.8V is the general value to apply to kv. So, 1050 X 14.8 = 15540rpm's, very low. You could turn a huge prop to compensate but here's the catch, larger props create more prop torque handling problems. Also, when large props cavitation then bite, they pull huge current surges, which can easily break parts. So, most have found, thru experience and school of hard knocks, that a prop speed of 30,000-38,000 yields a good compromise between these factors. Fast enough to run smaller props, less prop torque issues and the smaller prop has more manageable current surges. Also a smaller prop tends to stay in the water better, because you really want to avoid cavitation. But there's always rough water to deal with... I hope that helps you decide how you would like to proceed!