Steve, this is not a very efficient set up to run on a model.Or the real thing for that matter. There were only that many props on the Turbi in order to overcome, or lessen, the effects of cavitation (at about 2500RPM on the real thing) On yer model, even a Torpedo 800 on 12v revs at 5000 rpm, and the blades on a prop that small are not exactly.,,er, exact…so. On some early TBD boats with ungeared turbines there were two props per shaft, but this soon changed to one per as soon as the more efficient geared units came along,  Props as small as that on the pictured model turbi, and I am guessing at 25 or 30 mm have to be spun at a fair pace….(12000 rpm???) to produce max useful thrust. My Turbi has 3x30mm props of approximately the right blade shape (see my gallery)and has yet to run….I am undecided on the motor setup, and I suspect only experimentation will prove what works best, unless the owner of the boat pictured can give us a shout. It may be that with all those props indeed only 5000 rpm will be needed…who knows????      The only reason for using that many props on a Turbi model is looks, as its what makes a model Turbi what it is, it is bound to actually perform so much better with only one prop per shaft and a two bladed one at that. In later years the actual ship was converted to slightly larger single props…which must tell us something? Ashley