I am building a diesel electric sub. I have two motors turning the props which are 48V 125A DC marine electric motors (6.8 hp). I am supplying power to these motors via 4 12V 8D CAT Batteries wired in series. If I supply mechanical power to a 48V DC (6 hp) motor by means of a diesel engine, will this motor now become a generator which will be able to charge my 4 12V batteries, which in turn, power the 2 48V DC electric prop motors ? I am attempting to mimic the diesel / electric propulsion found on real subs, just in miniature form.

I'm trying to figure out what happens if I power the motor/generator without powering the prop motors. Does this charge the batteries ? If I power the motor/gen AND power the two prop motors, will the prop motors get their electrical current from the gen, or will they still draw from the batteries. If I power the gen and only power the prop motors and 1/4 speed, is the remaining 3/4 of unused current going to go to charging the batteries ? Do I need to use a 12V motor as my generator instead of a 48V given the fact that the 8D Cat batts are each 12V ?

Any sumbarine technicians in the crowd ?