Re: What is the ACC circuit?
The acronym or label "ACC" is sometimes used to mean accessories. The circuit breakers or switches on your electrical panel which are labeled as "ACC" are probably intended to feed branch circuits to which accessories can be connected whose load (in aggregate) will not exceed the current rating for that circuit.
It is impossible for a reader to know what exactly is connected to them on your boat. When boats leave their point of manufacture it is common for owners and users to modify the electrical power distribution on those boats in all sorts of ways. You will have to follow the wires coming from these circuits to see what might be attached to them.
Re the courtesy of previous replies as you commented:
"Thank you for explaining for circuit breakers do. I had no idea. I suppose I shouldn't expect any more courtesy in this forum than I get on the water."
You must understand that there is a phenomenon with boats which causes people who know absolutely nothing about electricity or wiring practices, and lack any experience in electric repair or diagnosis, to become empowered to work on the electrical systems of their own boats, and, because of this, it is common for people to ask questions without having any basic knowledge. There is something of an expectation that people asking for an explanation of electrical phenomenon are clueless, unless they demonstrate otherwise in their initial narrative.
As for asking for the definition of acronyms, I tend to use ACRONYMFINDER.COM to resolve unusual acronyms. For example,
http://www.acronymfinder.com/ACC.html
does show "accessory" as a possible meaning of the acronym "ACC."