Hi @Ferbin -
Using that calculator, and leaving the voltage at 12V, you’ll find that a single 12 gauge conductor 100’ long can only effecticely move about about 100 watts to the vehicle. That’s not very much, and it leaves one of the three conductors completely unused! If you use two cables, with three wires each, you could use about 300 watts, which is likely a reasonable amount for most ROV activities, if the gain is kept low at 25%…
However, two cables that long is going to be quite heavy, and encumber the ROV as it moves around!
I’d review your 100 foot requirement, and potentially look to source cable of another construction more locally (at a hardware store?) I would assume you aren’t allowed to boost the voltage going down the tether?
This guide has a whole section on this general problem…
It’s also worth noting that ArduSub has a parameter you can set that will attempt to limit the power consumption below a given setpoint (MOT_BAT_CURR_MAX) - you can also achieve this by lowering the max/min throttle points for all thrusters. See this thread for more detail.