When a large ship is piloted or guided into harbor or port with the assistance of a barge or tugboat, it is known as a ship assist. Ship assists are a vital part of maritime commerce, and they are offered at most major harbors, since large ships would be unable to dock without support. Numerous firms offer ship assist services, often at a multitude of ports so that customers can work with the same company in multiple places. In some regions, a ship assist is also called an escort.
Many consumer goods are moved by ship all over the world. The ships which carry consumer goods are gigantic, designed to carry huge loads of shipping containers which are dropped off in port and then trucked or transported by rail to other locations. These large ships tend to be very difficult to maneuver, as they are built for size, not speed and a small turning radius. On the open ocean, this is not an issue, but in harbor, it can become a liability.
As a result, many large ships are actually towed into harbor by small, highly maneuverable, very strong boats such as tugboats. Typically, a large ship will be boarded by a pilot when it approaches a harbor. The pilot actually steers the ship into port, since he or she is extensively familiar with the features and hazards of the harbor. If necessary, the pilot teams up with tugboats or barges to move the ship into place in the harbor.
Tugboats and barges work in a number of ways. Some tugs actively pull a ship, essentially using their extremely powerful engines to tow the ship. Others may push, rather than pulling, and tugboats usually work in teams or groups so that they have total control of the larger vessel. A tugboat is designed to be easy to maneuver, so that the boat can respond quickly to an assortment of situations which may arise during a ship assist. Conventionally, it is polite for other craft in the harbor to yield to a ship which is being towed, and also to give way to larger vessels in general.
A ship assist may also be offered to a distressed ships. Distressed ships may have lost power or steering ability, rendering them unable to reach safe port. Specialized tugs are designed for the open ocean so that they can reach these ships and bring them, along with their crews, to safety.