Hi slewis, I have a very similar sized launch to the triple and I spent some time working out battery life against planing speed.
I came up with a motor prop combination with an input of 12 volts and 3 amp current load giving 36 watts. I would go for the minimum power consumption that makes the boat plane. Any combination to give an answer of 36 -40 watts. 6 volts at 6-7 amps is the same power, as is 7.2 volts at 5 -6 amps, 8.4 volts at 4.5 - 5 amps. The propeller diameter and pitch determines how much current is used.
The battery (and charger) and motor and propeller are the power unit, I would settle on the first 2 and then try different propellers.
On my launch I tried going from 12 to 18 volts and it made only a marginal difference to the speed, the boat just settles lower in the water at the stern.
If you have not got one, a meter is a good investment,it must be able to read at least 10 amps on current. You put it in series with the battery and motor, without the RC ESC in the circuit, as some electronic meters do not like the pulsed output of the ESC.
Use light batteries NiMh, and be prepared to move them within the boat to adjust for planing. You will need more than one set of batteries at the lakeside. There is another approach to the battery choice. That is older lower Amp hour batteries and they are cheaper.
For instance. Howes models advertise 7.2 volt batteries at 2 Amp hr for £8.00. But newer NiMh cells 7.2 volts at 3.6 Amp hr for £25! You can buy 3 sets of the former cells for the price of the Nimh cells and have nearly twice as long on the water. There is an even better bargain with the 1.8 Amp hr batteries! Your choice!
A RC receiver with BEC will also save weight on receiver battery.
Hope this is of some help and regards to all Roy
