If the windlass was a factory fitted option then it will probably run off the house battery as was the norm for Dufour at the time. I think on later models it may run off the engine battery.
To rewire the windlass to run off the engine battery is quite a big task. Not only would you have to run the quite large positive lead back to the engine battery isolation switch you would also need to isolate the negative return behind the switch panel and then lead it back to the engine battery negative terminal. This is because certainly on our 36C the 2 battery circuits are independent of each other with no common negative terminal. The negatives were connected with a 30 amp wire to enable the house battery to be charged from the alternator but this would not cope with the 100 amps or so from the windlass.
So when I upgraded to lithium I looked around for a battery which would cope with demands of the windlass. I found a 208AH LiPO4 with a continuous current discharge rating of 150amps and a surge discharge rate of 300amps for 15 seconds. When I measured the current demands of the windlass it was about 110amps on start up and then 80-100amps during use.
In practice the lithium far outperforms the lead acid battery it replaced. Under load the voltage drop is negligible so the windlass no longer labours when pulling the anchor up and the chart plotter no longer shuts down due to low voltage.
Hope this helps
Andrew