I agree with Bill--the Windlass should be on its own circuit--all the way from a switch--directly to the battery, or the battery/bus.
The circuit is acting like a dead short--and Boris' suggestion is the first place to look. I would loosen the clutch, and see if the windlass gypsy turns by hand. Then again try the windlass switch up and down. There are a host of issues which can occur in that gear case--and it is even possible that the motor may run in up, yet not down.
I also agree that the windlass should be on the engine start battery, or at least a battery which is being charged when the engine is running. You want to start the engine, and power up until you are right over the anchor, using the windlass to take up the slack (not pull the boat forward), and then power the boat to break the anchor out--the windlass to pull the rode, and anchor up to the boat's anchor roller. These small boat windlasses are not as robust as some of their bigger brothers, which are rated for 3500 lbs are.
Since the house battery went to "0" voltage, it means that the windlass is wired to the house battery, and the suggestion that the battery be checked is also valid. However, letting the anchor down, is probably only a 10 amp load, if the windlass is working properly.