A
tugboat (
tug) is a boat that maneuvers vessels by pushing or towing them. Tugs move vessels that either should not move themselves, such as ships in a crowded harbor or a narrow canal, or those that cannot move by themselves, such as
barges, disabled ships,
log rafts, or
oil platforms. Tugboats are powerful for their size and strongly built, and some are ocean-going. Some tugboats serve as
icebreakers or
salvage boats. Early tugboats had
steam engines, but today most have
diesel engines. Many tugboats have
firefighting monitors, allowing them to assist in firefighting, especially in harbors.