Tugboats are used to pull or push ships and barges into and out of docks in ocean ports as well as river harbors. These mighty boats may also move disabled ships and oil platforms. They may also be used as icebreakers or salvage boats. Tugs were some of the first ships to be steam powered and today are now diesel powered. Many are now fitted for firefighting duty as well as their regular hauling duties.
A tugboat is designed for great might in a relatively small package. Most tugs use two separate engines and propellers. This two engine design ensures that the tug will be able to get a ship or barge to its destination without a breakdown that would require another tug to finish the job. Two engines also mean more power to do the work. Tugboat engines are usually 680 to 3,400 horsepower (Hp) each. Some large tugs even sport 27,000 Hp engines! Such engine power comes from engines that are also used in locomotive engines. Some tugs are even made just like railroad engines. These tugs use the diesel engines as electrical generators that run electric propeller motors.
Standard tugs use a hawser to pull ships. A hawser is a large, flexible steel or fiber rope. A standard tug has a pointed bow to give it good control in ocean waters as well as is rivers.
Notch tugs are designed to fit into a special notch in the rear of a barge, effectively making the two into one ship. An empty barge is less stable and controllable than one that is loaded, so notch tugs have a winch like a standard tug to pull empty barges.
There is a third category of tugs that is even more closely attached to its load than the rest. ITB, integrated tug and barge, and ATB, articulated tug and barge, are two methods of actually connecting tug to barge that make the two into one ship. In an ITB, the tug is locked solidly to a barge so that the tug and barge don't move against one another. In an ATB, the tug is firmly connected to the barge on pivots that allow the tug and barge to twist and rock against each other to reduce forces on both tug and barge caused by the wind and waves.
Notch, ITB, and ATB tugboats have flat bows rather than the pointed bows, allowing the tug to safely exert all of its power pushing against a barge while spreading the force across a long flat edge on both vessels.