For the Casco Bay ferry, a car isn't necessary right? When we get off the boat at each island, are they small enough to check out on foot?

Thinking of the Copley House for Boston home base: http://www.copleyhouse.com/

and the Inn at St. John for Portland home base:
http://innatstjohn.com/

Thinking about a rental car, but probably won't know for sure until a month or so out.