Dont forget, it does not really matter what the voltage of the motor is on the bow thruster, as to gte it to work properly, its always better to run it through an "esc", like you would a drive motor, so the voltage will vary and give you better control over the thruster power setting, so you can just use "light joystick control" and ease the boat sideways, or give it full stick and hit fuull power so to speak.
I have a 7.2v graupner thruster in my boat and the boat runs 12v main batteries.
I would not really recommend using a couple of micro switches to swop polarity on the thruster wires to change its direction over and it will always be in use on full power and that will rerely be needed in such mode.
