Both fall under the same subheading (890400), so the distinction does not affect the tariff line. Functionally, tugboats tow or assist vessels by pulling with a tow line, while pusher craft propel barges or other floating units by direct contact from behind. Both are classified here as long as their primary design purpose is maneuvering or propelling other vessels rather than carrying cargo.

Classification depends on the vessel's principal function. A workboat designed primarily for towing or pushing qualifies under 8904, but one whose primary purpose is cargo carriage, crew transport, or another function — with towing as incidental — would more likely fall under 8901 or 8906. The vessel's design specifications and intended use are the determining factors.