towboat -
A steamer used for towing other vessels; a tug.
Wikipedia
A towboat is a boat designed for pushing barges or car floats. Towboats are characterized by a square bow with steel knees for pushing and powerful engines. They are most often seen on inland waterways and western rivers where they can push more than 50 large barges lashed together into a tow of varying shapes and sizes.
OmegaWiki Dictionary
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towboat A towboat is a boat designed for pushing barges.