Proper Fusing
Fire on a boat is a serious thing. A fiberglass boat is fuel ready to burn and help too far away to do any good. For this reason, it is paramount that the right safety measures are taken when wiring a boat. As with home wiring, the fusing must protect the wire in the event of a short. Otherwise the wire will overheat and potentially catch on fire and cause lose of life and equipment. This video has rather poor audio but demonstrates this point well:
Unfortunately I think the advice here is rather incomplete. Yes, we want to protect the wire. But we also want to protect the downstream equipment as it can also short out and potentially cause a fire hazard. For this reason, the fuse must be the lower of what is needed to protect the wire and the equipment. If the wire calls for a 10 amp fuse but the equipment needs 5, you better put a 5 amp fuse. The 5 amp fuse will protect the wire just as well as the equipment. A 12 amp fuse will only protect the wire but let in considerable amount of current into the failing equipment.
As I noted: if you are at all uncomfortable with these concepts and/or have not taken the time to really educate yourself, you should not attempt to do the work yourself. Use this knowledge and review what is already done on your work to make sure it is safe. I routinely find that boat manufacturers violate these safety rules.