Brass props are usually much more efficient. With such a small boat why not use a modified servo as the drive motor/speed controller. You can then use AA cells to provide 4.8 or 6v for both radio and propulsion. You would need to provide some form of reduction from motor to prop. You can use the feedback pot in the servo to set your centre off position, and will have proportional fwd/rev to the motor. You will not achieve great speed with this set up but I assume you are thinking of launching and recovering the daughter boat from the parent vessel and will need good manouverability for this to work. if you want the speed then a 280 motor coupled with a small Mtronics esc or possible one of Action small speed controllers. Brass props can be had from many online stores. Better still visit one of the bigger shows and see what's on offer.
dave

HI dave,

thanks for the advise, been doing a bit of research on the web, moreso on some german model boats sites and they seem to suggest a 280 motor as suitable replacement. So yes, this should be the best way to go, all Ive got to do now is decide on if to go for a geared/reduction unit, or just use lower battery voltage to keep revs of the prop down.

Ive located some nice compact nicad packs [7.2v] and think that a pair of these should fit quite snugly in the hull, one on either side [for balance/weight distribution], plus keep the weight low down.

im definately going to discard the original mechanical power controller, but again, need to decide on a suitable controller for the motor.
I already have a spare electronic volt dropper to use for the reciever power supply, as that simply sends out a steady 5/6v output, but accepts between 6 and 18v input, so dont matter on main battery volts, the only restriction is the drive motor.

incidentally, whats your opinion on plakky props? would you leave alone, or replace for brass? this O E graupner one seems a bit flimsy and flexible....

yep sound like the graupner unit. They always were noisy even from new. I have one somewhere but will never use it, if I can find it you are welcome to have it. Personally I would use a small 200/300 motor with a direct drive or possibly a home made reduction using pulleys and o rings.
dave