usually it takes 5 knots/hour with fair weather and tugboats are in good condition

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. Towboats that travel long distances (linehaul) include living quarters for the crew. Outside of the USA towboats are usually referred to as "push boats" or "pushers".

Source: http://en.wikipedia.org/wiki/Towboat

Joseph C. Sturm has written:

'An estimation of river towboat air pollution in Saint Louis, Missouri' -- subject- s -: Air, Pollution, Towboats, Measurement

Michael M Bernitsas has written:

'Rational method for upgrading towed vessel safety' -- subject(s): Safety measures, Towboats, Towing, Inland navigation

Doreen Armitage has written:

'Around the Sound' -- subject(s): History

'From the Wheelhouse' -- subject(s): Histoire, History, Ship captains, Remorqueurs, Biographies, Tugboats, Pousseurs (Navigation), Capitaines de navire, Towboats, Biography