Мұзды суларда жүзуге арналған кемелер

Ship that is able to navigate through ice covered waters

An icebreaker is a special purpose ship or boat designed to move and navigate through ice covered waters, and provide safe waterways for other boats and ships. Although the term usually refers to ice breaking ships, 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. The efforts of the ice breaking barge were successful enough to warrant the town purchasing four such ships. Ice breaking barges continued to see use during the colder winters of the Little Ice Age with growing use in the Low Country where significant amounts of trade, and transport of people and goods took place. In the course of fifteenth century the use of ice breakers in Flanders (Oudenaarde, Kortrijk, Ieper, 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.

Ice strengthened ships were used in the earliest days of polar exploration. These were originally wooden and based on existing designs, but reinforced, particularly around the waterline with double planking to the hull and strengthening cross members inside the ship. Bands of iron were wrapped around the outside. Sometimes metal sheeting was placed at the bows, at the stern, and along the keel. Such strengthening was designed to help the ship push through ice and also to protect the ship in case it was "nipped" by the ice. Nipping occurs when ice floes around a ship are pushed against the ship, trapping it as if in a vise and causing damage. This vise like action is caused by the force of winds and tides on ice formations. The first boats to be used in the polar waters were those of the Eskimos. Their kayaks are small human powered boats with a covered deck, and one or more cockpits, each seating one paddler who strokes a single or double bladed paddle. Such boats have no icebreaking capabilities, but they are light and well fit to carry over the ice. 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 sailing ships, used for voyages in the ice conditions of the Arctic seas and later on Siberian 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 Norwegian 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.

An early ship designed to operate in icy conditions was a wooden paddle steamer, City Ice Boat No. 1, that was built for the city of Philadelphia by Vandusen & Birelyn in 1837. The ship was powered by two steam engines and her wooden paddles were reinforced with iron coverings. With a rounded shape and strong metal hull, the Russian Pilot 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 Yermak, 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 scrapped 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 CGS N. B. McLean (1930) and CGS D'Iberville (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.

Before the first diesel electric icebreakers were built in the 1930s, icebreakers were either coal or oil fired steam ships. During the steam era, the most powerful pre war steam powered icebreakers had a propulsion power of about Both vessels were decommissioned in the 1970s and replaced by much larger icebreakers in both countries, the 1976 built Sisu in Finland and the 1977 built Ymer in Sweden. 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 .

Russia currently operates all existing and functioning nuclear powered icebreakers. The first one, NS Lenin, 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. The second Soviet nuclear icebreaker was NS Arktika, the lead ship of the In service since 1975, she was the first surface ship to reach the North Pole, on August 17, 1977. Several nuclear powered icebreakers were also built outside the Soviet Union. Two shallow draft Taymyr class nuclear icebreakers were built in Finland for the Soviet Union in the late 1980s.

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. Some icebreakers are also used to support scientific research in the Arctic and Antarctic. In addition to icebreaking capability, the ships need to have reasonably good open water characteristics for transit to and from the polar regions, facilities and accommodation for the scientific personnel, and cargo capacity for supplying research stations on the shore. 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.

Icebreakers are often described as ships that drive their sloping bows onto the ice and break it under the weight of the ship. In reality, this only happens in very thick ice where the icebreaker will proceed at walking pace or may even have to repeatedly back down several ship lengths and ram the ice pack at full power. More commonly the ice, which has a relatively low flexural strength, is easily broken and submerged under the hull without a noticeable change in the icebreaker's trim while the vessel moves forward at a relatively high and constant speed. 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. 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. Short and stubby icebreakers are generally built using transverse framing in which the shell plating is stiffened with frames placed about apart as opposed to longitudinal framing used in longer ships. Near the waterline, the frames running in vertical direction distribute the locally concentrated ice loads on the shell plating to longitudinal girders called stringers, which in turn are supported by web frames and bulkheads that carry the more spread out hull loads. 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.

Since the Second World War, most icebreakers have been built with diesel electric propulsion in which diesel engines coupled to generators produce electricity for propulsion motors that turn the fixed pitch propellers. The first diesel electric icebreakers were built with direct current (DC) generators and propulsion motors, but over the years the technology advanced first to alternating current (AC) generators and finally to frequency controlled AC AC systems. 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. 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 through ice.

The steam powered icebreakers were resurrected in the late 1950s when the Soviet Union commissioned the first nuclear powered icebreaker, Lenin, in 1959. It had a nuclear turbo electric powertrain in which the nuclear reactor was used to produce steam for turbogenerators, which in turn produced electricity for propulsion motors. Starting from 1975, the Russians commissioned six Arktika class nuclear icebreakers. Soviets also built a nuclear powered icebreaking cargo ship, Sevmorput, which had a single nuclear reactor and a steam turbine directly coupled to the propeller shaft. Russia, which remains the sole operator of nuclear powered icebreakers, is currently building icebreakers to replace the aging Arktika class. The first vessel of this type entered service in 2020.

A hovercraft can break ice by the resonance method. This causes the ice and water to oscillate up and down until the ice suffers sufficient mechanical fatigue to cause a fracture.