I have used this size motor with 14.4v with no problem but I wouldn't exceed the voltage rating of the esc- you probably wouldn't get away with it for long.

My recent experience has shown that Lipo batteries are a great way of saving weight and delivering more amps to the motor. NiMh batteries tend to drop voltage a bit when a lot is asked of them whereas Lipos will give what the motor asks for.

That 700 motor would do well on a 3s Lipo and you could make adjustments to the prop size to manage speed and current draw. My Wavemaster in the video section has a 700 motor on parallel 3s cells- but the esc is an Electronize 30amp which can take more than 12v. I do use 3s batteries in another boat with 700 motors with a an Mtroniks 40amp esc which has a 12v limit.

There is a lot of info on the web and on here about using Lipo cells and determining current draw. The only sensible way forward is to be able to measure current draw with a wattmeter with the boat in the bath. This will then tell you what is going on with various props/motor/battery combinations. Buying one saved me a lot in burnt out esc's!
Good luck with it all.

Ian

hmm, interesting, I had assumed with the motors rated range I would be OK at 14.4v but I have no experience to go by and others do so point noted. I guess at the moment (or soon as she is ready to take to the water) I am not going to be looking at more than pottering around to get used to the thing so 7.2v is enough. When I get confident I will look at more options if I need to and yes, those two NiMh's are heavy! This whole matter of prop size/pitch/blades, motor rating/rpm and voltage is confusing, there must be some sort of formula for arriving at the optimum but everyone seems to use a different set-up, mostly found by what a technical manual I once read described as the 'emperical technique', or trial and error to the rest of us! Cheers anyway.

I have used 700 bb's in the past and to be honest, they dont like voltage over 12v. running 2 x 7.2v sticks is going to put you over at full speed, so be careful, as it will overheat the windings and damage it.

to increase the speed, it may be simpler to experiment with smaller prop size, rather than overvolt the motor.
If you want to run near optimum voltage, why not use an 11,1v lipo? it will also save on a lot of weight too.