A tugboat (tug) is a boat that maneuvers vessels by pushing or towing them. Tugs move vessels that either should not move themselves, such as ships in a crowded harbor or a narrow canal,or those that cannot move by themselves, such as barges, disabled ships, 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 have diesel engines. Many tugboats have firefighting monitors, allowing them to assist in firefighting, especially in harbors.
Types of tugboats
Seagoing tugboats are in three basic categories:
Historically tugboats were the first seagoing vessels with steam propulsion, providing freedom from the restraint of the wind. As such, they were employed in harbors to assist ships in docking and departure.
River tugs 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.
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) and 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 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.
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 WWII 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, 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: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 fiction
To date there have been three children's shows revolving around anthropomorphic tugboats. In the late 1980s, 13 episodes were made of TUGS. It had an American spinoff called Salty's Lighthouse. One of the creators of that series went on to make Theodore Tugboat. On Tugs, the models were able to move their heads and eyes and didn't have motors. On Theodore Tugboat, the models have motors and moving eyes.
Little Toot (1939) is a children's story that tells the 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.
The children's book Scuffy the Tugboat, 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, concerned the dangers faced by the crews of Dutch tug salvage tugs. The novella Stella, concerning the dangers faced by the captains of rescue tugs in the English Channel during WWII, was made into a film entitled The Key in 1958. The novel The Captain, about the captain of a rescue tug during a Murmansk Convoy, sold over a million copies. Its sequel, The Commodore, features the narrator captaining a fleet of tugs in peace-time.
Canadian writer Farley Mowat wrote the book The Grey Seas Under telling 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 Annie was the subject of a series of Saturday Evening Post magazine stories featuring the character of a 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.
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 Armadores II
Tugboat Angelina C
Tugboat Emilio Panfido
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