A dog without a tail is like a ship without a sail, would probably just swim in a circle.
I don't know about dobermans, I never tossed one off of a dock.
i've heard a long tail helps a dog migrate across a log on a river, creek, or branch.
they wave it back and forth, and it helps keep them balanced on the short diameter log.
i've never seen a coon-dog fall off a log into the creek. but i guess it could happen.