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An icebreaker is a special-purpose ship or boat designed to move and Ice navigation through ice-covered waters, and provide safe for other boats and ships. Although the term usually refers to ice-breaking , it may also refer to smaller vessels, such as the icebreaking boats that were once used on the canals of the United Kingdom.
For a ship to be considered an icebreaker, it requires three traits most normal ships lack: a strengthened hull, an ice-clearing shape, and the power to push through sea ice.
Icebreakers clear paths by pushing straight into frozen-over water or pack ice. The bending strength of sea ice is low enough that the ice breaks usually without noticeable change in the vessel's . In cases of very thick ice, an icebreaker can drive its bow onto the ice to break it under the weight of the ship. A buildup of broken ice in front of a ship can slow it down much more than the breaking of the ice itself, so icebreakers have a specially designed hull to direct the broken ice around or under the vessel. The external components of the ship's propulsion system (, Drive shaft, etc.) are at greater risk of damage than the vessel's hull, so the ability of an icebreaker to propel itself onto the ice, break it, and clear the debris from its path successfully is essential for its safety.
Ice breaking barges continued to see use during the colder winters of the Little Ice Age with growing use in the Low Countries where significant amounts of trade and transport of people and goods took place. In the 15th century the use of ice breakers in Flanders (Oudenaarde, Kortrijk, Ypres, Veurne, Diksmuide and Hulst) was already well established. The use of the ice breaking barges expanded in the 17th century where every town of some importance in the Low Country used some form of icebreaker to keep their waterways clear.
Before the 17th century the specifications of icebreakers are unknown. The specifications for ice breaking vessels show that they were dragged by teams of horses and the heavy weight of the ship pushed down on the ice breaking it. They were used in conjunction with teams of men with axes and saws and the technology behind them didn't change much until the industrial revolution.
In the 9th and 10th centuries, the Viking expansion reached the North Atlantic, and eventually Greenland and Svalbard in the Arctic. Vikings, however, operated their ships in the waters that were ice-free for most of the year, in the conditions of the Medieval Warm Period.
In the 11th century, in North Russia the coasts of the White Sea, named so for being ice-covered for over half of a year, started being settled. The mixed ethnic group of the Karelians and the Russians in the North-Russia that lived on the shores of the Arctic Ocean became known as Pomors ("seaside settlers"). Gradually they developed a special type of small one- or two-mast wooden , used for voyages in the ice conditions of the Arctic seas and later on rivers. These earliest icebreakers were called kochi. The koch's hull was protected by a belt of ice-floe resistant flush skin-planking along the variable water-line, and had a false keel for on-ice portage. If a koch became squeezed by the ice-fields, its rounded bodylines below the water-line would allow for the ship to be pushed up out of the water and onto the ice with no damage.
In the 19th century, similar protective measures were adopted to modern steam-powered icebreakers. Some notable sailing ships in the end of the Age of Sail also featured the egg-shaped form like that of Pomor boats, for example the Fram, used by Fridtjof Nansen and other great Norway Polar explorers. Fram was the wooden ship to have sailed farthest north (85°57'N) and farthest south (78°41'S), and one of the strongest wooden ships ever built.
With a rounded shape and strong metal hull, the Russian of 1864 was an important predecessor of modern icebreakers with propellers. The ship was built on the orders of merchant and shipbuilder Mikhail Britnev. She had the bow altered to achieve an ice-clearing capability (20° raise from keel line). This allowed Pilot to push herself on the top of the ice and consequently break it. Britnev fashioned the bow of his ship after the shape of old Pomor boats, which had been navigating icy waters of the White Sea and Barents Sea for centuries. Pilot was used between 1864 and 1890 for navigation in the Gulf of Finland between Kronstadt and Oranienbaum thus extending the summer navigation season by several weeks. Inspired by the success of Pilot, Mikhail Britnev built a second similar vessel Boy ("Breakage" in Russian) in 1875 and a third Booy ("Buoy" in Russian) in 1889.
The cold winter of 1870–1871 caused the Elbe River and the port of Hamburg to freeze over, causing a prolonged halt to navigation and huge commercial losses. Carl Ferdinand Steinhaus reused the altered bow Pilots design from Britnev to make his own icebreaker, Eisbrecher I. The first true modern sea-going icebreaker was built at the turn of the 20th century. Icebreaker , was built in 1899 at the Armstrong Whitworth naval yard in England under contract from the Imperial Russian Navy. The ship borrowed the main principles from Pilot and applied them to the creation of the first polar icebreaker, which was able to run over and crush pack ice. The ship displaced 5,000 tons, and her steam-reciprocating engines delivered . The ship was decommissioned in 1963 and Ship breaking in 1964, making her one of the longest serving icebreakers in the world.
In Canada, the government needed to provide a way to prevent flooding due to ice jam on the St. Lawrence River. Icebreakers were built in order to maintain the river free of ice jam, east of Montréal. In about the same time, Canada had to fill its obligations in the Canadian Arctic. Large steam icebreakers, like the (1930) and (1952), were built for this dual use (St. Lawrence flood prevention and Arctic replenishment).
At the beginning of the 20th century, several other countries began to operate purpose-built icebreakers. Most were coastal icebreakers, but Canada, Russia, and later, the Soviet Union, also built several oceangoing icebreakers up to 11,000 tons in displacement.
In 1941, the United States started building the . Research in Scandinavia and the Soviet Union led to a design that had a very strongly built short and wide hull, with a cut away forefoot and a rounded bottom. Powerful diesel-electric machinery drove two stern and one auxiliary bow propeller. These features would become the standard for postwar icebreakers until the 1980s.
Since the mid-1970s, the most powerful diesel-electric icebreakers have been the formerly Soviet and later Russian icebreakers Ermak, Admiral Makarov and Krasin which have nine twelve-cylinder diesel generators producing electricity for three propulsion motors with a combined output of . In the late 2020s, they will be surpassed by the new Canadian polar icebreakers and , which will have a combined propulsion power of .
Canada's largest and most powerful icebreaker, the , was delivered in 1969. Her original three steam turbine, nine generator, and three electric motor system produces . A multi-year mid-life refit project (1987–1993) saw the ship get a new bow, and a new propulsion system. The new power plant consists of five diesels, three generators, and three electric motors, giving about the same propulsion power.
On 22 August 1994 Louis S. St-Laurent and became the first North American surface vessels to reach the North Pole. The vessel was originally scheduled to be decommissioned in 2000; however, a refit extended the decommissioning date to 2017. It is now planned to be kept in service through the 2020s pending the introduction of two new polar icebreakers, and , for the Coast Guard.
In May 2007, were completed for the nuclear-powered Russian icebreaker NS . The vessel was put into service by Murmansk Shipping Company, which manages all eight Russian state-owned nuclear icebreakers. The keel was originally laid in 1989 by Baltic Works of Leningrad, and the ship was launched in 1993 as NS Ural. This icebreaker is intended to be the sixth and last of the Arktika class.
As offshore drilling moves to the Arctic seas, icebreaking vessels are needed to supply cargo and equipment to the drilling sites and protect the and from ice by performing ice management, which includes for example breaking drifting ice into smaller floes and steering away from the protected object. In the past, such operations were carried out primarily in North America, but today Arctic offshore drilling and oil production is also going on in various parts of the Russian Arctic. The United States Coast Guard uses icebreakers to help conduct search and rescue missions in the icy, polar oceans. United States icebreakers serve to defend economic interests and maintain the nation's presence in the Arctic and Antarctic regions. As the icecaps in the Arctic continue to melt, there are more passageways being discovered. These possible navigation routes cause an increase of interests in the polar hemispheres from nations worldwide. The United States polar icebreakers must continue to support scientific research in the expanding Arctic and Antarctica oceans. Every year, a heavy icebreaker must perform Operation Deep Freeze, clearing a safe path for resupply ships to the National Science Foundation's facility McMurdo in Antarctica. The most recent multi-month excursion was led by the Polar Star which escorted a container and fuel ship through treacherous conditions before maintaining the channel free of ice.
When an icebreaker is designed, one of the main goals is to minimize the forces resulting from crushing and breaking the ice, and submerging the broken floes under the vessel. The average value of the longitudinal components of these instantaneous forces is called the ship's ice resistance. who design icebreakers use the so-called h- v-curve to determine the icebreaking capability of the vessel. It shows the speed ( v) that the ship is able to achieve as a function of ice thickness ( h). This is done by calculating the velocity at which the thrust from the propellers equals the combined hydrodynamic and ice resistance of the vessel. An alternative means to determine the icebreaking capability of a vessel in different ice conditions such as pressure ridges is to perform model tests in an ice tank. Regardless of the method, the actual performance of new icebreakers is verified in full scale ice trials once the ship has been built.
In order to minimize the icebreaking forces, the hull lines of an icebreaker are usually designed so that the flare at the waterline is as small as possible. As a result, icebreaking ships are characterized by a sloping or rounded stem as well as sloping sides and a short parallel midship to improve maneuverability in ice. However, the spoon-shaped bow and round hull have poor hydrodynamic efficiency and seakeeping characteristics, and make the icebreaker susceptible to slamming, or the impacting of the bottom structure of the ship onto the sea surface. For this reason, the hull of an icebreaker is often a compromise between minimum ice resistance, maneuverability in ice, low hydrodynamic resistance, and adequate open water characteristics. Some icebreakers have a hull that is wider in the bow than in the stern. These so-called "reamers" increase the width of the ice channel and thus reduce frictional resistance in the aftship as well as improve the ship's maneuverability in ice. In addition to low friction paint, some icebreakers utilize an explosion-welded abrasion-resistant stainless steel ice belt that further reduces friction and protects the ship's hull from corrosion. Auxiliary systems such as powerful water deluges and air bubbling systems are used to reduce friction by forming a lubricating layer between the hull and the ice. Pumping water between tanks on both sides of the vessel results in continuous rolling that reduces friction and makes progress through the ice easier. Experimental bow designs such as the flat Thyssen-Waas bow and a cylindrical bow have been tried over the years to further reduce the ice resistance and create an ice-free channel.
If built according to the rules set by a classification society such as American Bureau of Shipping, Det Norske Veritas or Lloyd's Register, icebreakers may be assigned an ice class based on the level of ice strengthening in the ship's hull. It is usually determined by the maximum ice thickness where the ship is expected to operate and other requirements such as possible limitations on ramming. While the ice class is generally an indication of the level of ice strengthening, not the actual icebreaking capability of an icebreaker, some classification societies such as the Russian Maritime Register of Shipping have operational capability requirements for certain ice classes. Since the 2000s, International Association of Classification Societies (IACS) has proposed adopting an unified system known as the Polar Class (PC) to replace classification society specific ice class notations.
Although the diesel-electric powertrain is the preferred choice for icebreakers due to the good low-speed torque characteristics of the electric propulsion motors, icebreakers have also been built with diesel engines mechanically coupled to reduction gearboxes and controllable pitch propellers. The mechanical powertrain has several advantages over diesel-electric propulsion systems, such as lower weight and better fuel efficiency. However, diesel engines are sensitive to sudden changes in propeller revolutions, and to counter this mechanical powertrains are usually fitted with large flywheels or hydrodynamic couplings to absorb the torque variations resulting from propeller-ice interaction.
The 1969-built Canadian polar icebreaker CCGS Louis S. St-Laurent was one of the few icebreakers fitted with steam boilers and turbogenerators that produced power for three electric propulsion motors. It was later refitted with five diesel engines, which provide better fuel economy than steam turbines. Later Canadian icebreakers were built with diesel-electric powertrain.
Two Polar-class icebreakers operated by the United States Coast Guard, have a combined diesel-electric and mechanical propulsion system that consists of six diesel engines and three . While the diesel engines are coupled to generators that produce power for three propulsion motors, the gas turbines are directly coupled to the propeller shafts driving controllable pitch propellers. The diesel-electric power plant can produce up to while the gas turbines have a continuous combined rating of . CGC Polar Star History. United States Coast Guard. The number, type and location of the propellers depends on the power, draft and intended purpose of the vessel. Smaller icebreakers and icebreaking special purpose ships may be able to do with just one propeller while large polar icebreakers typically need up to three large propellers to absorb all power and deliver enough thrust. Some shallow draught have been built with four propellers in the stern. Ducted propeller may be used to increase the thrust at lower speeds, but they may become clogged by ice. Until the 1980s, icebreakers operating regularly in ridged ice fields in the Baltic Sea were fitted with first one and later two bow propellers to create a powerful flush along the hull of the vessel. This considerably increased the icebreaking capability of the vessels by reducing the friction between the hull and the ice, and allowed the icebreakers to penetrate thick ice ridges without ramming. However, the bow propellers are not suitable for polar icebreakers operating in the presence of harder multi-year ice and thus have not been used in the Arctic.
remove the need of traditional propellers and rudders by having the propellers in steerable gondolas that can rotate 360 degrees around a vertical axis. These thrusters improve propulsion efficiency, icebreaking capability and maneuverability of the vessel. The use of azimuth thrusters also allows a ship to move astern in ice without losing manoeuvrability. This has led to the development of double acting ships, vessels with the stern shaped like an icebreaker's bow and the bow designed for open water performance. In this way, the ship remains economical to operate in open water without compromising its ability to operate in difficult ice conditions. Azimuth thrusters have also made it possible to develop new experimental icebreakers that operate sideways to open a wide channel through ice.
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