They are not confined to any set channels. When out in open water, they move as they please. For example, the Staten Island Ferry follows a general route from which it can veer quite sharply as it crosses New York s Upper Bay. A paddler crossing the harbor can t be absolutely certain where that ferry will intersect his path. Since there is no ferry channel there is no easy way to tell whether you are out of its way.
Ferries are highly maneuverable.
Unlike a tanker or a freighter, ferries have a relatively short stopping distance. Some of them can turn on a dime. Again, back to that Staten Island Ferry. I was once on one with a local industrial archaeology group that was allowed on the bridge. While discussing the propulsion of the craft, the skipper demonstrated how it could turn totally around inside of its own space.