The ferry is on demand from the Dewees Island side: in order to save resources, the ferry doesn't run if there are no riders. This means you must call the ferry at 843-568-3990 to reserve a spot back to the mainland. The crew only keeps track of the calls for that hour, so you need to call between the time the boat leaves Dewees (at 30 minutes past the hour) and the time it arrives on the Isle of Palms (50 minutes past the hour) and the captain needs to decide which ferry to use. Be sure to tell them how many people and pets, as well as how much luggage.