The ocean steamship lines require an auxiliary fleet of harbor vessels as tenders to them. Of these, the most numerous are the tow-boats, or tugs, as they are popularly called. There are 375 tow-boats registered at New York, but fully 400 float on the waters in the vicinity of the city. About 50 tow-boats have a gross tonnage of over 100 tons. Among the largest are the Amboy, of 272 tons, and the Luckenback, an ocean tug, of 255 tons. Still larger than these are the Vanderbilt and Oswego, the side-wheelers which pull the long strings of canal-boats up and down the Hudson. The tow-boats are fitted with powerful engines, and the facility with which one little tug will pull a ship many times her size, or a dozen canal-boats, is a marvel to the visitor from inland districts. The most powerful of these tugs have engines of 900 indicated horse-power, and of the type known as the fore-and-aft, or tandem. Two of these harbor tugs, the Amboy and the Raritan, both belonging to the Pennsylvania Railroad Company, have been operated with twin screws for twenty years at least. Less than twenty-five per cent. of the freight trade of the country is carried on by ships flying the Stars and Stripes. During the calendar year of 1890, 33,359 vessels engaged in foreign trade entered at the ports of the United States. Their total tonnage was 18,510,374. American vessels, to the number of 11,033, carried 4,334,774 tons of the total amount, and foreign ships handled 14,175,600 tons. The merchant marine of the United States has a total tonnage of 4,424,497. The coastwise fleet has an aggregate tonnage of 3,409,435; the foreign trade, 928,062; and vessels registering 87,000 tons are engaged in the cod and whale fisheries. The vessels belonging to the port of New York in 1890 were 1,976 sailing vessels, of 409,468 tons; 1,032 steam vessels, of 374,673 tons; 230 canal boats, of 23,709 tons; and 671 barges, of 143,540 tons.