The house batteries are totally separate, with their own alternator .
The engine alternator, with its own Kubota regulator, charges two new identical batteries in parallel, one to start the engine and one at the windlass. They are separate when the engine is not running.
Wire engine to starting battery amidships is 2/0. Wire going onward to the windlass battery in the bow is #6 AWG
The windlass battery sees about 14.2 volts when the engine is running. By chance, we have motored about 6 hours the past two days while working on the windlass, so the battery is quite well charged.

I just measured the voltage drop across the power supply circuit breaker that trips. It is less than 0.05 volts
However the drop across the Lofrans relay that operates the up/down is 1.3 volts on the up side and 1.1 on the down side, both with the windlass drawing 170 amps with no chain on the gypsy.