Voltage increasing via regulator
If you just want to boost the bow thruster why don't you just fit a small 12V (or 11.1V LiPo) just for that? Frankly I might start with an 9.6V batt before I jump from 7.2 to 12V.
I assume it's just either On or OFF, i.e. no ESC.
As you can see from the specs of your Booster, as the output volts increase the deliverable current (for a given input volts) decreases inversely, as I predicted! Ya don't get summat for nuttin!
Soooo, you need to carefully check the specs of the thruster motor;
max voltage, current at maximum efficiency versus volts applied!
That will tell you the max volts battery that you can safely and most efficiently use, and you can check if your booster can deliver the required current at the voltage needed. I'd just use a separate battery and a servo operated micro switch, but then I'm just a dumb engineer!😲
Bon chance mon ami👍 Cheers, Doug 😎