Holy Hanna was that hard to read.
void between the top of the deck and the inside overhead
I assume you are referring to how modern, mass produced,boats are commonly made Vs a structural defect in the deck coring or fiberglass layup.
Windlass mounting:
-Cut a hole in the overhead
-install the windlass to the deck, with a substantial backing plate
-make an attractive, removable, panel that covers the backing plate.
You will likely notice that your boat already has factory installed,removable panels, where other deck hardware is mounted.
(Photos of the mounting location would help people assist you)
0 cable is pretty expensive install battery closer to winch ?
Windlass power cables:
If you install the existing batteries closer to the winch, you would then need to extend the other wiring (with larger gauge) to the new location. No real cost+time benefit there.
If you add batteries forward, just for the windlass.. you would likely use a second dc charger with smaller cables feeding it. (In that case you had better hope you don't use the windlass too much over a short time, otherwise the charger can't keep up)
3 options for the cable size...
1) get a 24 volt windlass and set your boat up to use both 12 and 24 volt circuits. (24 volt circuits can use smaller gauge wire)
2) spend the money for the 12 volt large gauge wire..it's a boat and they aren't cheap.
3) use a manual windlass
Personally I would use option 2. Installing a 12V windlass with a long cable run is likely to be the cheapest, simplest, and lightest solution unless you want to do it manually.
