A tug (tugboat) is a boat or ship that maneuvers vessels by pushing or towing them. Tugs move vessels that either should not move by themselves, such as ships in a crowded harbor or a narrow canal, or those that could not move by themselves, such as barges, disabled ships, log rafts, or oil platforms. Tugboats are powerful for their size and strongly built, and some are ocean-going. Some tugboats serve as icebreakers or salvage boats. Early tugboats had steam engines, but today most have diesel engines. Many tugboats have firefighting monitors, allowing them to assist in firefighting, especially in harbors.
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Types of tugboats
Deep-sea tugs
Seagoing tugs (deep-sea tugs or ocean tugboats) fall into four basic categories:
- The standard seagoing tug with model bow that tows its "payload" on a hawser.
- The "notch tug" which can be secured in a notch at the stern of a specially designed barge, effectively making the combination a ship. This configuration is dangerous to use with a barge which is "in ballast" (no cargo) or in a head- or following sea. Therefore, "notch tugs" are usually built with a towing winch. With this configuration, the barge being pushed might approach the size of a small ship, with interaction of the water flow allowing a higher speed with a minimal increase in power required or fuel consumption.
- The "integral unit", or "integrated tug and barge" (ITB), comprises specially designed vessels that lock together in such a rigid and strong method as to be certified as such by authorities (classification societies) such as the American Bureau of Shipping, Lloyd's Register of Shipping, Indian Register of Shipping, Det Norske Veritas or several others. These units stay combined under virtually any sea conditions and the tugs usually have poor sea-keeping designs for navigation without their barges attached. Vessels in this category are legally considered to be ships rather than tugboats and barges must be staffed accordingly. These vessels must show navigation lights compliant with those required of ships rather than those required of tugboats and vessels under tow.
- "Articulated tug and barge" (ATB) units also utilize mechanical means to connect to their barges. The tug slips into a notch in the stern and is attached by a hinged connection. ATBs generally utilize Intercon and Bludworth connecting systems. ATBs are generally staffed as a large tugboat, with between seven and nine crew members. The typical American ATB operating on the east coast customarily displays navigational lights of a towing vessel pushing ahead, as described in the 1972 ColRegs.
Harbour tugboats
Compared to seagoing tugboats, harbour tugboats are generally smaller and their width-to-length ratio is often higher, due to the need for a lower draught. In smaller harbours these are often also termed lunch bucket boats, because they are only manned when needed and only at a minimum (captain and deckhand), thus the crew will bring their own lunch with them. The number of tugboats in a harbour varies with the harbour infrastructure and the types of tugboats. Things to take into consideration includes ships with/without bow thrusters and forces like wind, current and waves and types of ship (e.g. in some countries there is a requirement for certain numbers and sizes of tugboats for port operations with gas tankers).
River tugboats
River tugs are also referred to as towboats or pushboats. Their hull designs would make open ocean operation dangerous. River tugs usually do not have any significant hawser or winch. Their hulls feature a flat front or bow to line up with the rectangular stern of the barge, often with large pushing knees.
Tugboat propulsion
Tugboat engines typically produce 500 to 2,500 kW (~ 680 to 3,400 hp), but larger boats (used in deep waters) can have power ratings up to 20,000 kW (~ 27,200 hp). Tugboats usually have an extreme power:tonnage-ratio; normal cargo and passenger ships have a P:T-ratio (in kW:GRT) of 0.35 to 1.20, whereas large tugs typically are 2.20 to 4.50 and small harbour-tugs 4.0 to 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 diesel-electric locomotives. For safety, tugboats' engines often feature two of each critical part for redundancy.
A tugboat's power is typically stated by its engine's horsepower and its overall bollard pull. The largest commercial harbour tugboats in the 2000s-2010s, used for towing container ships or similar, had around 60-65 tons of bollard pull, which is described as 15 tons above "normal" tugboats.
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 and was 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 Aquamaster or Schottel system, many brands exist: Steerprop, Wärtsilä, Berg Propulsion, etc. These 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.
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-to-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 recent Dutch innovation is the Carousel Tug, winner of the Maritime Innovation Award at the Dutch Maritime Innovation Awards Gala in 2006. The Carousel Tug adds a pair of interlocking rings to the body of the tug, the inner ring attached to the boat, with the outer ring attached to the towed ship by winch or towing hook. Since the towing point rotates freely, the tug is very difficult to capsize.
The Voith Schneider propeller (VSP), also known as a cycloidal drive is a specialized marine propulsion system. It is highly maneuverable, being able to change the direction of its thrust almost instantaneously. It is widely used on tugs and ferries.
From a circular plate, rotating around a vertical axis, a circular array of vertical blades (in the shape of hydrofoils) protrude out of the bottom of the ship. Each blade can rotate itself around a vertical axis. The internal gear changes the angle of attack of the blades in sync with the rotation of the plate, so that each blade can provide thrust in any direction, very similar to the collective pitch control and cyclic in a helicopter.
Tugboats in popular culture
Tugboat Annie was the subject of a series of Saturday Evening Post magazine stories featuring the female captain of the tugboat Narcissus in Puget Sound, later featured in the films Tugboat Annie (1933), Tugboat Annie Sails Again (1940) and Captain Tugboat Annie (1945). The Canadian television series The Adventures of Tugboat Annie was filmed in 1957.
Film and television
To date, there have been four children's shows revolving around anthropomorphic tugboats.
- In the late 1980s, 13 episodes were made of TUGS, a series depicting the life of tugboats in the 1920s.
- An American adaptation followed: Salty's Lighthouse.
- One of the creators of that series went on to make Theodore Tugboat.
- Animated preschool series Toot the Tiny Tugboat started broadcasting on Channel 5 Milkshake! in 2014 and on Cartoonito in 2015, with a Welsh language version airing on S4C Cyw.
"Tugger" is a tugboat in the animated series South Park. He appears in the episode "The New Terrance and Phillip Movie Trailer" as a sidekick for Russell Crowe in a fictitious television series entitled Fightin' Round The World with Russell Crowe. Tugger follows Crowe as he engages various people in physical conflicts, providing emotional support and comic relief. At one point Tugger even attempts to commit suicide, upon being forced to hear Russell Crowe's new musical composition.
Literature
(Alphabetical by author)
- The children's book Scuffy the Tugboat, written by Gertrude Crampton and illustrated by Tibor Gergely and first published in 1946 as part of the Little Golden Books series, follows the adventures of a young toy tugboat who seeks a life beyond the confines of a tub inside his owner's toy store.
- The Dutch writer Jan de Hartog wrote numerous nautical novels, first in Dutch, then in English.
- The novel Hollands Glorie, written prior to World War II, was made into a Dutch miniseries in 1978 and concerned the dangers faced by the crews of Dutch salvage tugs.
- The novella Stella, concerning the dangers faced by the captains of rescue tugs in the English Channel during World War II, was made into a film entitled The Key in 1958.
- The novel The Captain (1967), about the captain of a rescue tug during a Murmansk Convoy, sold over a million copies.
- Its 1986 sequel, The Commodore, features the narrator captaining a fleet of tugs in peace-time.
- Little Toot (1939), written and illustrated by Hardie Gramatky, is a children's story of an anthropomorphic tugboat child, who wants to help tow ships in a harbour near Hoboken. He's rejected by the tugboat community and dejectedly drifts out to sea, where he accidentally discovers a shipwrecked liner and a chance to prove his worth.
- Farley Mowat's book The Grey Seas Under tells the tale of a legendary North Atlantic salvage tug, the Foundation Franklin. He later wrote The Serpent's Coil, which also deals with salvage tugs in the North Atlantic.
Tugboat races
Vintage Tugboat races have been held annually in Olympia, Washington since 1974 during the Olympia Harbor Days Maritime Festival (www.HarborDays.com). Tugboat races are held annually on Elliott Bay in Seattle, on the Hudson River at the New York Tugboat Race, the Detroit River, and the Great Tugboat Race and Parade (2012 event was on June 29-30) on the St. Mary's River.
Tugboat ballet
Since 1980, an annual tugboat ballet has been held in Hamburg harbour on the occasion of the festival commemorating the anniversary of the establishment of a port in Hamburg. On a weekend in May, eight tugboats perform choreographed movements for about an hour to the tunes of waltz and other sorts of dancing music.
Tugboat moors at container ship
Source of the article : Wikipedia
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