Tugboat (redirected from Steam tug)

tugboat, small, strongly built vessel, used to guide large oceangoing ships into and out of port and to tow barges, dredging and salvage equipment, and disabled vessels. Tugboats range in overall length from 70 to 210 ft (21–64 m), and their engines generate from 750 to 3,000 horsepower. Steam power dominated tugboat design until diesel and diesel-electric drives were developed. Most tugs are built of wood or metal-sheathed wood; the resiliency of a wooden hull prevents damage to both tugboat and vessel in berthing operations.

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tugboat [′təg‚bōt]

(naval architecture)

A powerful, strongly built boat with shaped hull and bow, designed to tow or push other vessels or barges in harbors, on inland waterways, and at sea.

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Tugboat 

a self-propelled ship used for towing nonself-propelled vessels, rafts, and other floating structures. Tugboats are used on the ocean, on rivers, on lakes, and in harbors. They are divided according to their functions into the following categories: towing tugboats, which pull other vessels by means of a towline; maneuvering tugboats, which aid ships in the process of docking and mooring; pusher tugboats, which push ships rather than pull them; and rescue tugboats, which assist ships disabled on the high seas and tow them to a safe harbor.

A tugboat’s function determines the pull on its tow hook and the power of its main engines. Harbor tugboats have engines of up to 150 kilowatts (kW), or 200 horsepower; modern rescue tugboats have engines of 6,000-7,000 kW (8,000-9,000 horsepower) and more. Tugboats are fitted with towing gear, which is the aggregate of equipment used for securing and paying out the towline with which the tug tows other ships, rafts, and so on. This equipment consists of a tow hook, attached to a hinge and rotating around the towing rail; towing arches; and trunnion caps (or shackles). The hook is often replaced by a towing winch, which maintains constant tension on the towline. The tow hook provides long-range payout of the towline; on harbor tugboats it provides automatic reduction in the height of the suspension in case of a change from longitudinal to lateral towing pull in order to prevent capsizing.

B. P. KHABUR and E. G. LOGVINOVICH