tugboat n : a powerful small boat designed to pull or push larger ships [syn: tug, towboat, tower]

English

Noun

1. a small, powerful boat used to push or pull barges or to help maneuver larger vessels

Synonyms

• tug

Translations

• Finnish: hinaaja
• Russian: буксир
• Spanish: remolcador

See also

• towboat

For the journal of digital typography, see TUGboat.

For alternative meanings of tug, see Tug (disambiguation).''

A tugboat, or tug, is a boat used to maneuver, primarily by towing or pushing, other vessels (see shipping) in harbours, over the open sea or through rivers and canals. Tugboats are also used to tow barges, disabled ships, or other equipment like towboats.

Tugboat design

Tugboats are quite strong for their size. Early tugboats had steam engines (see steamboat); today diesel engines are used. Tugboat engines typically produce 750 to 3,000 horsepower (500 to 2,000 kW), but larger boats (used in deep waters) can have power ratings up to 25,000 hp (20,000 kW) and usually have an extreme power:tonnage-ratio (normal cargo and passenger ships have a P:T-ratio, kW:GRT, of 0.35-1.20, whereas large tugs typically are 2.20-4.50 and small harbour-tugs 4.0-9.5). The engines are often the same as those used in railroad locomotives, but typically drive the propeller mechanically instead of converting the engine output to power electric motors, as is common for railroad engines. For safety, tugboats' engines feature two of each critical part for redundancy.

Tugboats are highly maneuverable, and various propulsion systems have been developed to increase maneuverability and increase safety. The earliest tugs were fitted with paddle wheels, but these were soon replaced by propeller-driven tugs. Kort nozzles have been added to increase thrust per kW / hp. This was followed by the nozzle-rudder, which omitted the need for a conventional rudder. The cycloidal propeller was developed prior to World War II but was only occasionally used in tugs because of its maneuverability. After World War II it was also linked to safety due to the development of the Voith Water Tractor, a tugboat configuration which could not be pulled over by its tow. In the late 1950s, the Z-drive or (azimuth thruster) was developed. Although sometimes referred to as the Schottel system, many brands exist: Schottel, Z-Peller, Duckpeller, Thrustmaster, Ulstein, Wärtsilä, etc. The propulsion systems are used on tugboats designed for tasks such as ship docking and marine construction. Conventional propeller/rudder configurations are more efficient for port-to-port towing.

A tugboat's power is typically stated by its engine's horsepower and its overall Bollard pull.

The Kort nozzle is a sturdy cylindrical structure around a special propeller having minimum clearance between the propeller blades and the inner wall of the Kort nozzle. The thrust:power ratio is enhanced because the water approaches the propeller in a linear configuration and exits the nozzle the same way. The Kort nozzle is named after its inventor, but many brands exist.

A new type of tugboat has been invented in the Netherlands. The so-called carousel tug consists of a design wherein the flexibility and effectiveness of the tugboat's maneuvers is determined not by the propulsion system, but by a steel construction on deck, consisting of two steel rings. The inner ring is fixed to the ship, and the second ring rotates freely and carries a hook or winch. The ship can therefore maneuver freely and independently of the towed ship, and since the towing point rotates towards the point nearest to the towed ship, the tug can capsize only with difficulty. One prototype exists presently, but the first new tugs are expected to sail in spring 2007.

Types of tugboats

There are two groups of tugboats, either Inland or Oceangoing.

Inland tugboats come in two categories: Harbor or Harbour tugs are the most typical of the tugboats that people recognize. They are used worldwide to move ships in and out of berth and to move industrial barges around waterfront business complexes. Their job has remained the same, but their design and engineering has changed much over the decades. Harbor tugs have evolved from paddle wheelers to the conventional tug known by all, and now to the Ship Docking Moduals and tractor tugs in the modern industry.

River tugs are also referred to as towboats or pushboats. They are designed as large squared-off vessels with flat bows for connecting with the rectangular stern of the barges. They are large and powerful, most commonly seen on the big rivers of the world. They are capable of pushing huge fleets of barges that are lashed together into "tows". Some tows can be up to 1,000 feet long and 205 feet wide. Smaller push boats are often seen handling only a few barges on inland waters. Despite their size, they are designed to push their tow rather than tow from the stern.

Oceangoing tugboats come in four categories:

The conventional tug is the standard seagoing tugboat with a model bow that tows its payload on a hawser; hawser is the nautical term for a long steel cable or large synthetic fiber rope. It operates independently and is used to tow various loads, e.g., cargo barges, ships, oil rigs, etc. This is the most versatile method of towing since the conventional tugboat is able to move its load three ways: Pushing from behind, secured to the side of the towed vessel, or by towing astern, all achieved by the use of various lines and cables in various configurations. They are importantly recognized as the design of choice for salvage and assistance of wrecked ships and in the rescue and safe return of disabled ships from the high seas.

The notch tug is a conventional tug which is assigned to tow and push a specific barge, usually built to the shape and specifications of that tugboat. A notch tug has a large towing winch on its stern, but it gets its name from the deep notch built into the stern of the barge. This notch is built in the exact shape of the tug's forward hull and can be quite deep, up to 90 feet, sometimes more. The tugboat fits snugly into the notch of the barge, and with the use of various lines can be secured firmly enough to push the barge at much higher speeds than it would if it were towing. The towing hawser remains rigged during pushing. In the event that the seas get too rough to push safely, the tug merely releases any securing lines and backs out of the notch while extending its towing hawser. Once in calmer waters, the tug can maneuver back into the notch and resume pushing. Voith Schneider Propeller in action

See also

• Azipod
• Towboat

References

• On Tugboats: Stories of Work and Life Aboard / Virginia Thorndike - Down East Books, 2004.
• Under Tow: A Canadian History of Tugs and Towing / Donal Baird - Vanwell Publishing, 277 p., 2003 - ISBN 1551250764
• Primer of Towing / George H. Reid - Cornell Maritime Press, 1992.
• South Park- Episode 83, Russell Crow Beats people up around the world and has a tugboat as a companion.

External links

• Voith-Schneider Propeller
• Novatug Carrousel Tug

Some pictures of tugboats and tugboat building

• 18 m. Steel Tug Boat Dilovası pn dry dock and harbor
• 25 m. Steel Tug Boat Dogancay on the sea
• Huge propellers of 32 m. Steel Tug Boat Captain Emre Omur
• Hull of 32 m. Tug Boat Sheba
• You can find some more tugboat examples from here
• NYC's Annual Tugboat Races