Towboat

[Becky]

A vessel constructed for being towed, as a canal boat.

[Dianne]

A self-propelled vessel which moves other, usually non-self-propelled vessels. May be in the form of a pushboat, a square- or flat-bow boat designed to rigidly connect to a [barge] or barges for the purpose of pushing it or them along a waterway. Not quite the same as a tugboat, which usually assists ships.