Instruct: Given a question, retrieve passages that can help answer the question.
Query: What is the biggest icebreaker ship in existence?
The icebreakers have also been used for a number of scientific expeditions in the Arctic. On August 17, 1977, Arktika was the first surface vessel in the world to reach the North Pole. Since 1989, some icebreakers have been used for Arctic tourist cruises.
SS "Manhattan" was an oil tanker constructed at the Fore River Shipyard in Quincy, Massachusetts that became the first commercial ship to cross the Northwest Passage in 1969. Having been built as an ordinary tanker in 1962, she was refitted for this voyage with an icebreaker bow in 1968–69. Registered in the United States at the time, she was the largest US merchant vessel as well as the biggest icebreaker in history. 
Double acting ship is a type of icebreaking ship designed to run ahead in open water and thin ice, but turn around and proceed astern (backwards) in heavy ice conditions. In this way, the ship can operate independently in severe ice conditions without icebreaker assistance but retain better open water performance than traditional icebreaking vessels.
In May 2007, sea trials 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 was intended to be the sixth and last of the "Arktika" class, and currently is the world's largest icebreaker.
Trans Viking Icebreaking & Offshore is an icebreaker shipping company. A joint venture between Viking Supply Ships and Rederi Transatlantic the company operates three icebreakers on contract with the Swedish Maritime Administration for icebreaking in the Baltic Sea from January through March. Commercial management is handled by VSS while Transatlantic is responsible for technical management.
"Avance" was offered to the city of Stockholm in 1907, but the Swedish buyers decided that she was too expensive and broke off the deal. Maintaining the icebreaker turned out to be more expensive than what was anticipated, and in 1909 the city of Turku purchased the majority of the shipping company's shares.
After the newest and most powerful state-owned icebreakers, "Voima" and "Jääkarhu", were handed over to Soviet Union as war reparations, Finland was left with four old steam-powered icebreakers and the small diesel-electric "Sisu", which had been rejected due to the extensive damage it had sustained in the war. The newest steam-powered icebreaker, "Tarmo", was almost 40 years old and along with the others long overdue for replacement — even the largest Finnish icebreakers were not wide and powerful enough to assist the biggest post-war cargo ships. There was also a severe shortage of coal and occasionally the Finnish icebreakers had to rely on firewood. The steam-powered icebreakers were completely overhauled for the last time in 1951–1952 when they finally received modern navigation equipment — even as late as 1952 some had neither gyrocompass, sonar nor radar — and their crew spaces were rebuilt to modern standards. There were talks about converting the furnaces of "Sampo" from coal to oil, but it was not deemed necessary as the old icebreaker was due to decommissioning in the near future.
Since even ships of ice class 1A Super are assumed to rely on icebreaker assistance from time to time, a research was conducted recently about introducing a new ice class exceeding all existing ice classes, 1A Super+, for ships capable of independent operation in all ice conditions and therefore reducing the need of icebreaker assistance in some ports. These ships could also be granted "icebreaker status" and their higher operating costs could be partially covered by government subsidies from the same funds that are used to cover the cost of icebreaker assistance. the new ice class has not been implemented in the Finnish-Swedish ice class rules.
The Coast Guard has acknowledged that it is not just "Louis S. St. Laurent" that is old, and needs replacing, all its icebreakers are old. Some critics have argued that with global warming, and the scramble for Arctic nations to document claims to a share of the Arctic Ocean seafloor, Canada lacked sufficient icebreakers. In 2018 the Coast Guard started to publicly search for existing large, capable icebreakers it could purchase. On August 13, 2018, the Coast Guard confirmed it would be buying and retrofitting three large, icebreaking, anchor-handling tugs, , and from Viking Supply Ships.
The result was, in many respects, the most advanced icebreaker in the world at the time. Although bow propellers had been a common feature in icebreakers around the world for decades, it was incorrectly believed that they helped with the actual icebreaking process by reducing the pressure under the ice in front of the ship. However, extensive research and recent experiences had shown that bow propellers improved the icebreaking capability because their flushing effect reduced the friction between the broken ice floes and the hull of the ship. The drawback of a single bow propeller was that it would lubricate only one side of the hull. As a result, the new Finnish icebreaker was designed with two bow propellers which would produce a more powerful and, more importantly, symmetric flushing effect. Furthermore, a vessel with four propellers would be extremely maneuverable and capable of even moving sideways. Prior to the new Finnish icebreaker, only the 1947-built Canadian ferry "Abegweit" had been fitted with such propulsion arrangement. While the new ship was not the most powerful icebreaker in the world at the time, the power-to-displacement and power-to-beam ratios of the new Finnish icebreaker put her in a class of her own among icebreaking ships.
The construction of the first Finnish post-war icebreaker was awarded to Wärtsilä in 1948, but due to lack of funding the keel of the ship was not laid down at the Hietalahti shipyard until 29 May 1951. The working name of the newbuilding was "Into", but when she was launched on 27 November 1952, the new Finnish icebreaker was christened "Voima" by Sylvi Kekkonen, wife of the Prime Minister and future President of Finland, Urho Kekkonen. Her name, Finnish for "strength", had previously been given to one of the icebreakers that had been handed over to the Soviet Union after the war. The official sea trials were completed on 12 February 1954 and on the following day "Voima" was handed over to the Finnish Maritime Administration.
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.
While the existing Finnish icebreaker fleet was owned and operated solely by Arctia, the new icebreaker was initially intended to be owned by the Finnish Transport Agency and the operator would be selected through public tendering process. The new model was adopted from Sweden where the operation of state-owned icebreakers has been open for competition for years. Arctia, which practically has a monopoly in the icebreaker business in Finland, has been criticized for higher prices when compared to Swedish icebreakers as well as potentially subsidizing unprofitable offshore operations by charging premium charter from the Finnish Transport Agency for the multipurpose vessels. In October 2014, the newly appointed Finnish Minister of Transport Paula Risikko (National Coalition Party) questioned her predecessors' decision to order the icebreaker for an expert organization operating under the jurisdiction of the Ministry of Transport and Communications instead of the state-owned shipping company which was established to own and manage the Finnish state-owned icebreaker fleet. In November 2014, the Ministry of Transport and Communications proposed the Finnish Transport Agency that the new icebreaker should be sold to Arctia. On 5 March 2015, it was officially announced that the Finnish Government had agreed to sell the new icebreaker to Arctia Icebreaking, a subsidiary of Arctia, for 128 million euro. Although the contract was officially signed on 20 April 2015, the ownership will be transferred when the vessel has been delivered in 2016. According to the contract, the shipping company is obliged to have the new icebreaker available for tendering procedures for Baltic Sea icebreaking services until the end of 2020.
Although icebreaking cargo ships had been built in the past, their hull forms were always compromises between open water performance and icebreaking capability. A good icebreaking bow, designed to break the ice by bending it under the ship's weight, has very poor open water characteristics and is subjected to slamming in heavy weather. However, a hydrodynamically efficient bulbous bow greatly increases the ice resistance, making it unsuitable for icebreakers. As a result, the total efficiency of icebreaking ships is 20–40% less than that of good open water vessels of similar size mainly due to the bow form.
The hull form of the ship, a result of intensive model tests in both open water and model ice, was very different from that of conventional merchant vessels, being more akin to polar icebreakers than traditional cargo ships. However, in addition to good icebreaking and manoeuvring capabilities in various ice conditions the vessel had to be able to operate in open water without bottom slamming or shipping of green water occurring in rough seas. Despite the compromises the ship had impressive icebreaking capability — the SA-15 class ships were designed to break level ice up to one metre () in thickness with a snow layer of in continuous motion without icebreaker assistance. The ships were also the first freighters in ten years to be built to the highest Soviet ice class notation available for merchant ships, ULA.
The following icebreaking supply ships have been used in the Caspian oil fields:The following lists include icebreakers owned and/or operated by both government-owned as well as commercial entities.The following ships are anchor handling tug supply vessels, platform supply vessels, research vessels, patrol vessels or other multipurpose vessels with significant icebreaking capability.
Three icebreaking anchor handling tug supply vessels were chartered by the Swedish Maritime Administration for escort icebreaking duties in the Baltic Sea until 2015.
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. Naval architects 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.
Today, most icebreakers are needed to keep trade routes open where there are either seasonal or permanent ice conditions. While the merchant vessels calling ports in these regions are strengthened for navigation in ice, they are usually not powerful enough to manage the ice by themselves. For this reason, in the Baltic Sea, the Great Lakes and the Saint Lawrence Seaway, and along the Northern Sea Route, the main function of icebreakers is to escort convoys of one or more ships safely through ice-filled waters. When a ship becomes immobilized by ice, the icebreaker has to free it by breaking the ice surrounding the ship and, if necessary, open a safe passage through the ice field. In difficult ice conditions, the icebreaker can also tow the weakest ships.
The development of the oblique icebreaker concept began in 1997, when Kværner Masa-Yards Arctic Technology Centre (MARC) established a project to develop new ways of assisting large tankers in ice conditions. Traditionally, escorting large ships up to wide required two conventional icebreakers with a beam of , a practice that was not very efficient and economical. Analysis of Finnish harbour statistics and icebreaker logbooks showed that with a beam of , the icebreaker would be wide enough to provide assistance to most merchant ships in need of towing. The larger ships, fewer in number, could then be assisted with an unconventional method. The result was an asymmetrical, triangle-shaped vessel with three azimuth thrusters in the "corners" pushing the icebreaker with a 50-degree angle of attack — almost sideways — in ice. Model tests in an ice tank showed that the proposed concept was viable and that the resistance of a large cargo ship was considerably reduced in both level ice as well as frozen brash ice when operating behind the oblique icebreaker. The concept has been patented.
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 river icebreakers have been built with four propellers in the stern. Nozzles 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.
Azimuth thrusters 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 though ice.
On 24 May 1956, Wärtsilä and Sudoimport, the Soviet foreign trade organization with a monopoly for the foreign trade of ships, signed a shipbuilding contract for the construction of two polar icebreakers. While only half as powerful as the 44,000hp "Lenin", the new icebreakers featured the most powerful diesel-electric power plant ever installed on a ship at the time. The Soviet negotiators had additional requirements for deep draught and fuel consumption, which Wahlforss promised Wärtsilä to reach. In practice, the demands put the company's engineering expertise to a tough test. At the end, however, Wärtsilä could deliver what Wahlforss had promised. Few years later, Wärtsilä received a follow-up order for three more icebreakers of the same design.
The hull form of the ship, a result of intensive model tests in both open water and model ice, was very different from that of conventional merchant vessels, being more akin to polar icebreakers than traditional cargo ships. However, in addition to good icebreaking and manoeuvring capabilities in various ice conditions the vessel had to be able to operate in open water without bottom slamming or shipping of green water occurring in rough seas. Despite the compromises the ship had impressive icebreaking capability — the SA-15 class ships were designed to break level ice up to one metre () in thickness with a snow layer of in continuous motion without icebreaker assistance. These ships were also the first freighters in ten years to be built to the highest Soviet ice class notation available for merchant ships, ULA.
The development of the icebreaker designated as LK-25 dates back to the first long-term plans for rebuilding the Russian icebreaker fleet after the dissolution of the Soviet Union. As part of these plans that were published in the early 1990s, a number of both conventional and nuclear-powered icebreaker designs were proposed, ranging from 7-megawatt auxiliary icebreakers (LK-7) operating near large ports to 110-megawatt nuclear icebreakers (LK-110N) capable of breaking ice up to thick. Of these, the 25-megawatt line icebreakers (LK-25) were intended to escort merchant ships and lead convoys through freezing seas, and operate as auxiliary ships in complex convoys along the Northern Sea Route. During the summer season, they could also escort ships independently over shallow waters in the Arctic.
In 2001 Fortum ordered two double acting Aframax tankers from Sumitomo Heavy Industries Ltd., Japan, to replace the company's older tankers that, because of their lower ice class, had traffic restrictions during the worst part of the winter and could not deliver their cargo all the way to the refineries in Porvoo and Naantali because they were not given icebreaker assistance. When this happened, the oil had to be transported to smaller ships of higher ice class at the edge of the ice — a practice that was both uneconomical and hazardous. The new ships are equipped with one pulling-type 16 MW Azipod unit — the most powerful ice-strengthened pod ABB has ever produced — and have the highest Finnish-Swedish ice class, 1A Super. They are designed to be capable of independent navigation and icebreaking in Baltic ice conditions with a possibility to operate also in the Pechora Sea. The ships follow the double acting principle with a bulbous bow for open water performance and stern designed with icebreaking performance in mind. The first double acting tanker, "Tempera", was delivered in 2002 and its sister ship, "Mastera", in 2003. The icebreaking capability of the vessels proved to be superior to other ships — in shuttle service between Primorsk, Russia, and the Finnish refineries the tankers required no icebreaker assistance and even acted as icebreakers for other merchant ships. The ships can break level ice up to thick at when operating astern.
The hull form of the SA-15 class ships, a result of intensive model tests in both open water and model ice, is very different from that of conventional merchant vessels, being more akin to polar icebreakers than traditional cargo ships. The bow design puts equal emphasis on both icebreaking and seakeeping characteristics, meaning that in addition to good icebreaking and manoeuvring capabilities in various ice conditions the vessel must be able to operate in open water without bottom slamming or shipping of green water occurring in rough seas. The sides are flared to prevent the ship from stopping or being damaged when operating in compressive ice fields. The aft part of the hull, while a compromise between good reversing qualities in the ice and low level of propeller-induced vibrations in the stern, is also designed to prevent pieces of ice from coming in contact with the propeller. The ships are also equipped with stern notches similar to those found in icebreakers, but instead of towing other ships they are meant to be used to allow safe assistance from icebreakers in particularly difficult ice conditions.
Russia currently operates all existing and functioning nuclear-powered icebreakers. The first one, NS , was launched in 1957 and entered operation in 1959, before being officially decommissioned in 1989. It was both the world's first nuclear-powered surface ship and the first nuclear-powered civilian vessel.