Yep earthed is what I would call it, but some electrical
pro will correct us !
Just remember that if the current finds it way into you boats circuits you might arc
some of it.
Can't see why you would need to remove the batteries, just take the negative clamp off?
I would be more concerned with protecting the fittings on the Davits
, even if you don't want to remove them just break metal to metal contacts with a non conductor , insulation
tape or a bit of thin rubber mat
Grp won't conduct, (carbon fibre might... I wouldn't chance it) but mind the splatter!!! ...Makes a hell of a mess on gel coat !