I installed the usual 12v/gas fridges in the past...they run on either, obviously, with options to run them off 240v and 24v. If you have 24v for starter motors and windlass then you need some pretty heavy battery cable running there, albeit the final terminations to the starters and windlass are usually about 4 or 6mm, and often less, for the final 300mm. However, you have options to tap off these as you head from battery compartment to the bow where the windlass is...
personally, leave those big boys alone, to do their job. Separate starting batteries and domestic batteries, with an extra set for specific loads such as radio/electronics. The relatively small spaces on board mean that LEDs are just amazing for internal lighting, rather than the old-fashioned 12v bc bulbs from Halfords which drain those batteries rapidly!
My last boat had all lighting and auxiliary circuits run in 4mm singles in custom-made teak conduits! Ah, those craftsmen! Beautiful teak channels, with brass screws every 15cm, varnished and unobtrusive, simply works of art! Blended in with the rest of the interior, but even in the underseat lockers, they used the same. Anyway, I digress...modern electronics and LED lighting fed initially by 4mm singles, no creep, plenty scope to tee-off. Clearly, I'm not advocating teak channels, but the principle is the same...fine stranded absorbs moisture, plus for the relatively short runs, solid conductors don't break the bank.
Just saying what worked for me...and that boat is still sailing, 40 years on.
