Digby's Disaster is the fifth episode of Season 4.
In the process of welcoming Dartmouth, a big, shiny, modern cable ship, the tugs ignore their friend Digby, a small, crusty, old cable ship. In fact, they are so busy fawning over Dartmouth, no one notices that one of the big ship's cables has slipped no one except Digby, that is. When Digby saves the cable from being cut on some rocks, the tugs apologize for ignoring him. And even the well-equipped Dartmouth asks for Digby's help.