That is a great Windlass.
We know the anchor and chain are not heavy enough to load the motor. So the problem should be friction in the gearbox. I am a big help ??

I would simply take apart a standard servo and make it into the drive for the windlass. Done it many times as a ESC for small boats. The pulses of the servo will jar the windlass several times a second and give fantastic control up and down.

Rich