Pretty sure you don’t want to use an aluminum boat as a ground like you would a car or truck frame. I would run a dedicated ground wire back to the negative terminal. As pal alluded to, it seems to be an open invite to electrolysis damage. That being said, I do not have any experience wiring in boats other than troubleshooting and replacing batteries and hooking up chargers.
Convinced me. Went out a few days ago and hooked all the grounds up to one wire and ran to the battery. This is probably why I'm not an electrician! Light's still all work.
