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An icebreaker is a special-purpose
ship A ship is a large watercraft, vessel that travels the world's oceans and other Waterway, navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally disti ...
or
boat A boat is a watercraft of a large range of types and sizes, but generally smaller than a ship, which is distinguished by its larger size or capacity, its shape, or its ability to carry boats. Small boats are typically used on inland waterways s ...
designed to move and navigate through
ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...
-covered waters, and provide safe
waterway A waterway is any Navigability, navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other ways. A first distinction is ...
s for other boats and ships. Although the term usually refers to ice-breaking
ship A ship is a large watercraft, vessel that travels the world's oceans and other Waterway, navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally disti ...
s, it may also refer to smaller vessels, such as the icebreaking boats that were once used on the
canals of the United Kingdom The canals of the United Kingdom are a major part of the network of inland waterways in the United Kingdom. They have a History of the British canal system, varied history, from use for irrigation and transport, through becoming the focus of the ...
. 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 Sea ice arises as seawater freezes. Because ice is less density, dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world' ...
. 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 trim. 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 (
propeller A propeller (often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon a working flu ...
s, propeller shafts, 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.


History


Earliest icebreakers

Prior to ocean-going ships, ice breaking technology was developed on inland canals and rivers using laborers with axes and hooks. The first recorded primitive icebreaker ship was a barge used by the Belgian town of
Bruges Bruges ( , ; ; ) is the capital and largest city of the province of West Flanders, in the Flemish Region of Belgium. It is in the northwest of the country, and is the sixth most populous city in the country. The area of the whole city amoun ...
in 1383 to help clear the town moat. 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 The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. Mat ...
with growing use in the Low Country where significant amounts of trade and transport of people and goods took place. In the 15th century the use of ice breakers in
Flanders Flanders ( or ; ) is the Dutch language, Dutch-speaking northern portion of Belgium and one of the communities, regions and language areas of Belgium. However, there are several overlapping definitions, including ones related to culture, la ...
(
Oudenaarde Oudenaarde (; ; in English sometimes ''Oudenarde'') is a Belgium, Belgian City status in Belgium, city and Municipalities of Belgium, municipality in the Flemish Region, Flemish Provinces of Belgium, province of East Flanders. The municipality ...
,
Kortrijk Kortrijk ( , ; or ''Kortrik''; ), sometimes known in English as Courtrai or Courtray ( ), is a Belgian City status in Belgium, city and Municipalities in Belgium, municipality in the Flemish Region, Flemish Provinces of Belgium, province of We ...
, Ieper,
Veurne Veurne (; , ) is a City status in Belgium, city and Municipalities in Belgium, municipality in the Belgium, Belgian Provinces of Belgium, province of West Flanders. The municipality comprises the town of Veurne proper and the settlements of , , ...
,
Diksmuide (; ; ) is a Belgian city and municipality in the Flemish province of West Flanders. The municipality comprises the city of proper and the former communes of Beerst, Esen, Kaaskerke, Keiem, Lampernisse, Leke, Nieuwkapelle, Oostkerke ...
and
Hulst Hulst () is a Municipalities of the Netherlands, municipality and city in southwestern Netherlands in the east of Zeelandic Flanders. History Hulst received City rights in the Netherlands, city rights in the 12th century. Hulst Siege of 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.


Sailing ships in the polar waters

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 The waterline is the line where the hull of a ship meets the surface of the water. A waterline can also refer to any line on a ship's hull that is parallel to the water's surface when the ship is afloat in a level trimmed position. Hence, wate ...
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
Eskimo ''Eskimo'' () is a controversial Endonym and exonym, exonym that refers to two closely related Indigenous peoples: Inuit (including the Alaska Native Iñupiat, the Canadian Inuit, and the Greenlandic Inuit) and the Yupik peoples, Yupik (or Sibe ...
s. Their
kayaks ] A kayak is a small, narrow human-powered watercraft typically propelled by means of a long, double-bladed paddle. The word ''kayak'' originates from the Inuktitut word '' qajaq'' (). In British English, the kayak is also considered to be ...
are small human-powered boats with a covered deck, and one or more cockpits, each seating one
paddler Canoeing is an activity which involves paddling a canoe with a single-bladed paddle. In some parts of Europe, canoeing refers to both canoeing and kayaking, with a canoe being called an 'open canoe' or Canadian. A few of the recreational forms ...
who strokes a single or double-bladed
paddle A paddle is a handheld tool with an elongated handle and a flat, widened end (the ''blade'') used as a lever to apply force onto the bladed end. It most commonly describes a completely handheld tool used to propel a human-powered watercraft by p ...
. 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 Viking expansion was the historical movement which led Norsemen, Norse explorers, traders and warriors, the latter known in modern scholarship as Vikings, to sail most of the North Atlantic, reaching south as far as North Africa and east as fa ...
reached the
North Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...
, and eventually
Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...
and
Svalbard Svalbard ( , ), previously known as Spitsbergen or Spitzbergen, is a Norway, Norwegian archipelago that lies at the convergence of the Arctic Ocean with the Atlantic Ocean. North of continental Europe, mainland Europe, it lies about midway be ...
in the Arctic.
Vikings Vikings were seafaring people originally from Scandinavia (present-day Denmark, Norway, and Sweden), who from the late 8th to the late 11th centuries raided, pirated, traded, and settled throughout parts of Europe.Roesdahl, pp. 9� ...
, however, operated their ships in the waters that were ice-free for most of the year, in the conditions of the
Medieval Warm Period The Medieval Warm Period (MWP), also known as the Medieval Climate Optimum or the Medieval Climatic Anomaly, was a time of warm climate in the North Atlantic region that lasted from about to about . Climate proxy records show peak warmth occu ...
. In the 11th century, in North Russia the coasts of the
White Sea The White Sea (; Karelian language, Karelian and ; ) is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the nort ...
, 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 The Arctic Ocean is the smallest and shallowest of the world's five oceanic divisions. It spans an area of approximately and is the coldest of the world's oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, ...
became known as Pomors ("seaside settlers"). Gradually they developed a special type of small one- or two-mast wooden
sailing ship A sailing ship is a sea-going vessel that uses sails mounted on Mast (sailing), masts to harness the power of wind and propel the vessel. There is a variety of sail plans that propel sailing ships, employing Square rig, square-rigged or Fore-an ...
s, used for voyages in the ice conditions of the Arctic seas and later on
Siberia Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...
n rivers. These earliest icebreakers were called
kochi Kochi ( , ), List of renamed Indian cities and states#Kerala, formerly known as Cochin ( ), is a major port city along the Malabar Coast of India bordering the Laccadive Sea. It is part of the Ernakulam district, district of Ernakulam in the ...
. 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 Portage or portaging ( CA: ; ) is the practice of carrying water craft or cargo over land, either around an obstacle in a river, or between two bodies of water. A path where items are regularly carried between bodies of water is also called a '' ...
. 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 The Age of Sail is a period in European history that lasted at the latest from the mid-16th (or mid-15th) to the mid-19th centuries, in which the dominance of sailing ships in global trade and warfare culminated, particularly marked by the int ...
also featured the egg-shaped form like that of Pomor boats, for example the '' Fram'', used by
Fridtjof Nansen Fridtjof Wedel-Jarlsberg Nansen (; 10 October 1861 – 13 May 1930) was a Norwegian polymath and Nobel Peace Prize laureate. He gained prominence at various points in his life as an explorer, scientist, diplomat, humanitarian and co-founded the ...
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.


Steam-powered icebreakers

An early ship designed to operate in icy conditions was a wooden
paddle steamer A paddle steamer is a steamship or steamboat powered by a steam engine driving paddle wheels to propel the craft through the water. In antiquity, paddle wheelers followed the development of poles, oars and sails, whereby the first uses were wh ...
, ''City Ice Boat No. 1'', that was built for the city of
Philadelphia Philadelphia ( ), colloquially referred to as Philly, is the List of municipalities in Pennsylvania, most populous city in the U.S. state of Pennsylvania and the List of United States cities by population, sixth-most populous city in the Unit ...
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 of 1864 was an important predecessor of modern icebreakers with propellers. The ship was built on the orders of merchant and shipbuilder
Mikhail Britnev Mikhail Osipovich Britnev (; 1822–1889) was a Russian shipowner and shipbuilder, who created the first metal- hull icebreaker named ''Pilot'' in 1864.Barents Sea The Barents Sea ( , also ; , ; ) is a marginal sea of the Arctic Ocean, located off the northern coasts of Norway and Russia and divided between Norwegian and Russian territorial waters.World Wildlife Fund, 2008. It was known earlier among Russi ...
for centuries. ''Pilot'' was used between 1864 and 1890 for navigation in the
Gulf of Finland The Gulf of Finland (; ; ; ) is the easternmost arm of the Baltic Sea. It extends between Finland to the north and Estonia to the south, to Saint Petersburg—the second largest city of Russia—to the east, where the river Neva drains into it. ...
between
Kronstadt Kronstadt (, ) is a Russian administrative divisions of Saint Petersburg, port city in Kronshtadtsky District of the federal cities of Russia, federal city of Saint Petersburg, located on Kotlin Island, west of Saint Petersburg, near the head ...
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 Hamburg (, ; ), officially the Free and Hanseatic City of Hamburg,. is the List of cities in Germany by population, second-largest city in Germany after Berlin and List of cities in the European Union by population within city limits, 7th-lar ...
to freeze over, causing a prolonged halt to navigation and huge commercial losses. Carl Ferdinand Steinhaus reused the altered bow ''Pilot''s 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 Sir W G Armstrong Whitworth & Co Ltd was a major British manufacturing company of the early years of the 20th century. With headquarters in Elswick, Tyne and Wear, Elswick, Newcastle upon Tyne, Armstrong Whitworth built armaments, ships, locomot ...
naval yard in
England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
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 engine A reciprocating engine, more often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common features of al ...
s 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 The St. Lawrence River (, ) is a large international river in the middle latitudes of North America connecting the Great Lakes to the North Atlantic Ocean. Its waters flow in a northeasterly direction from Lake Ontario to the Gulf of St. Lawren ...
. Icebreakers were built in order to maintain the river free of ice jam, east of
Montréal Montreal is the List of towns in Quebec, largest city in the Provinces and territories of Canada, province of Quebec, the List of the largest municipalities in Canada by population, second-largest in Canada, and the List of North American cit ...
. 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 The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
, also built several oceangoing icebreakers up to 11,000 tons in displacement.


Diesel-powered icebreakers

Before the first diesel-electric icebreakers were built in the 1930s, icebreakers were either coal- or oil-fired
steam ship A steamship, often referred to as a steamer, is a type of steam-powered vessel, typically ocean-faring and seaworthy, that is propelled by one or more steam engines that typically move (turn) propellers or Paddle steamer, paddlewheels. The fir ...
s. Reciprocating steam engines were preferred in icebreakers due to their reliability, robustness, good torque characteristics, and ability to reverse the direction of rotation quickly. During the steam era, the most powerful pre-war steam-powered icebreakers had a propulsion power of about . The world's first diesel-electric icebreaker was the 4,330-ton Swedish icebreaker in 1933. At divided between two propellers in the stern and one propeller in the bow, she remained the most powerful Swedish icebreaker until the commissioning of in 1957. ''Ymer'' was followed by the Finnish , the first diesel-electric icebreaker in Finland, in 1939. Both vessels were decommissioned in the 1970s and replaced by much larger icebreakers in both countries, the 1976-built in Finland and the 1977-built 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 . In the late 2020s, they will be surpassed by the new Canadian polar icebreakers and , which will have a combined propulsion power of .


Canada

In Canada, diesel-electric icebreakers started to be built in 1952, first with HMCS ''Labrador'' (was transferred later to the Canadian Coast Guard), using the USCG Wind-class design but without the bow propeller. Then in 1960, the next step in the Canadian development of large icebreakers came when was completed at Lauzon, Quebec. A considerably bigger and more powerful ship than ''Labrador'', ''John A.Macdonald'' was an ocean-going icebreaker able to meet the most rigorous polar conditions. Her diesel-electric machinery of was arranged in three units transmitting power equally to each of three shafts. 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.


Nuclear-powered icebreakers

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
currently operates all existing and functioning
nuclear-powered Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced b ...
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. The second Soviet nuclear icebreaker was NS , the lead ship of the . In service since 1975, she was the first surface ship to reach the
North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True North Pole to distingu ...
, 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. In May 2007,
sea trial A sea trial or trial trip is the testing phase of a watercraft (including boats, ships, and submarines). It is also referred to as a "shakedown cruise" by many naval personnel. It is usually the last phase of construction and takes place on op ...
s were completed for the nuclear-powered Russian icebreaker NS . The vessel was put into service by
Murmansk Murmansk () is a port city and the administrative center of Murmansk Oblast in the far Far North (Russia), northwest part of Russia. It is the world's largest city north of the Arctic Circle and sits on both slopes and banks of a modest fjord, Ko ...
Shipping Company, which manages all eight Russian state-owned nuclear icebreakers. The keel was originally laid in 1989 by Baltic Works of
Leningrad Saint Petersburg, formerly known as Petrograd and later Leningrad, is the List of cities and towns in Russia by population, second-largest city in Russia after Moscow. It is situated on the Neva, River Neva, at the head of the Gulf of Finland ...
, and the ship was launched in 1993 as NS ''Ural''. This icebreaker is intended to be the sixth and last of the ''Arktika'' class.


Function

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 Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...
, the
Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...
and the
Saint Lawrence Seaway The St. Lawrence Seaway () is a system of rivers, locks, canals and channels in Eastern Canada and Northern United States that permits oceangoing vessels to travel from the Atlantic Ocean to the Great Lakes of North America, as far inland ...
, and along the
Northern Sea Route The Northern Sea Route (NSR) (, shortened to Севморпуть, ''Sevmorput'') is a shipping route about long. The Northern Sea Route (NSR) is the shortest shipping route between the western part of Eurasia and the Asia-Pacific region. Ad ...
, 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.Segercrantz, H. (1989): Icebreakers — Their Historical and Technical Development. ''Interdisciplinary Science Reviews'', Vol 14, No. 1. Some icebreakers are also used to support scientific research in the
Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...
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. Countries such as
Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
and
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
, which do not require icebreakers in domestic waters, have research icebreakers for carrying out studies in the polar regions. As
offshore drilling Offshore drilling is a mechanical process where a wellbore is drilled below the seabed. It is typically carried out in order to explore for and subsequently extract petroleum that lies in rock formations beneath the seabed. Most commonly, the ter ...
moves to the Arctic seas, icebreaking vessels are needed to supply cargo and equipment to the drilling sites and protect the
drillship A drillship is a merchant vessel designed for use in exploratory offshore drilling of new oil and gas wells or for scientific drilling purposes. In recent years the vessels have been used in deepwater and ultra-deepwater applications, equipped ...
s and
oil platform An oil platform (also called an oil rig, offshore platform, oil production platform, etc.) is a large structure with facilities to extract and process petroleum and natural gas that lie in rock formations beneath the seabed. Many oil platforms w ...
s from ice by performing ice management, which includes for example breaking drifting ice into smaller floes and steering
iceberg An iceberg is a piece of fresh water ice more than long that has broken off a glacier or an ice shelf and is floating freely in open water. Smaller chunks of floating glacially derived ice are called "growlers" or "bergy bits". Much of an i ...
s 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 The United States Coast Guard (USCG) is the maritime security, search and rescue, and Admiralty law, law enforcement military branch, service branch of the armed forces of the United States. It is one of the country's eight Uniformed services ...
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
Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...
oceans. Every year, a heavy icebreaker must perform
Operation Deep Freeze Operation Deep Freeze is the code name for a series of United States missions to Antarctica, beginning with "Operation Deep Freeze I" in 1955–56, followed by "Operation Deep Freeze II", "Operation Deep Freeze III", and so on. (There was an init ...
, clearing a safe path for resupply ships to the
National Science Foundation The U.S. National Science Foundation (NSF) is an Independent agencies of the United States government#Examples of independent agencies, independent agency of the Federal government of the United States, United States federal government that su ...
'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.


Characteristics


Ice resistance and hull form

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 Flexural strength, also known as modulus of rupture, or bend strength, or transverse rupture strength is a material property, defined as the Stress (mechanics), stress in a material just before it Yield (engineering), yields in a flexure test. T ...
, 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.National Research Council (2007)
Polar Icebreakers in a Changing World: An Assessment of U.S. Needs
The National Academies Press, Washington D.C.
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 architect This is the top category for all articles related to architecture and its practitioners. {{Commons category, Architecture by occupation Design occupations Occupations Occupation commonly refers to: *Occupation (human activity), or job, one's rol ...
s 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 Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...
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 A flare, also sometimes called a fusée, fusee, or bengala, bengalo in several European countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illuminatio ...
at the waterline is as small as possible. As a result, icebreaking ships are characterized by a sloping or rounded
stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...
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 Seakeeping ability or seaworthiness is a measure of how well-suited a watercraft is to conditions when underway. A ship or boat which has good seakeeping ability is said to be very seaworthy and is able to operate effectively even in high sea stat ...
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.


Structural design

Icebreakers and other ships operating in ice-filled waters require additional structural strengthening against various loads resulting from the contact between the hull of the vessel and the surrounding ice. As ice pressures vary between different regions of the hull, the most reinforced areas in the hull of an icegoing vessel are the bow, which experiences the highest ice loads, and around the waterline, with additional strengthening both above and below the waterline to form a continuous ice belt around the ship.Chapter 5 Ship Design and Construction for Ice Operations
Canadian Coast Guard.
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. While the shell plating, which is in direct contact with the ice, can be up to thick in older polar icebreakers, the use of high strength steel with
yield strength In materials science and engineering, the yield point is the point on a stress–strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and w ...
up to in modern icebreakers results in the same structural strength with smaller material thicknesses and lower steel weight. Regardless of the strength, the steel used in the hull structures of an icebreaker must be capable of resisting brittle fracture in low ambient temperatures and high loading conditions, both of which are typical for operations in ice-filled waters. If built according to the rules set by a
classification society A ship classification society or ship classification organisation is a non-governmental organization that establishes and maintains technical standards for the construction and operation of Shipping, ships and Offshore platform, offshore structure ...
such as
American Bureau of Shipping The American Bureau of Shipping (ABS) is an American maritime classification society established in 1862. Its stated mission is to promote the security of life, property, and the natural environment, primarily through the development and verific ...
,
Det Norske Veritas Det Norske Veritas (DNV), formerly DNV GL, is an international accredited registrar and classification society headquartered in Høvik, Norway. DNV provides services for several industries, including maritime, oil and gas, renewable energy, e ...
or
Lloyd's Register Lloyd's Register Group Limited, trading as Lloyd's Register (LR), is a technical and professional services organisation and a maritime classification society, wholly owned by the Lloyd’s Register Foundation, a UK charity dedicated to research ...
, icebreakers may be assigned an
ice class Ice class refers to a notation assigned by a classification society or a national authority to denote the additional level of strengthening as well as other arrangements that enable a ship to navigate through sea ice. Some ice classes also have ...
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 The Russian Maritime Register of Shipping (RMRS) () maintains a ship registration, ship register of the Russia, Russian Federation, based in Saint Petersburg, and is a marine classification society. Its activities aim to enhance safety of naviga ...
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.


Power and propulsion

Since the
Second World War World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, 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 Direct current (DC) is one-directional electric current, flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor (material), conductor such as a wire, but can also flow throug ...
(DC) generators and propulsion motors, but over the years the technology advanced first to
alternating current Alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC), which flows only in one direction. Alternating current is the form in w ...
(AC) generators and finally to frequency-controlled AC-AC systems. In modern diesel-electric icebreakers, the propulsion system is built according to the power plant principle in which the main generators supply electricity for all onboard consumers and no auxiliary engines are needed. 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 propeller Controllability is an important property of a control system and plays a crucial role in many regulation problems, such as the stabilization of unstable systems using feedback, tracking problems, obtaining optimal control strategies, or, simply p ...
s. 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 The United States Coast Guard (USCG) is the maritime security, search and rescue, and Admiralty law, law enforcement military branch, service branch of the armed forces of the United States. It is one of the country's eight Uniformed services ...
, have a combined diesel-electric and mechanical propulsion system that consists of six diesel engines and three
gas turbine A gas turbine or gas turbine engine is a type of Internal combustion engine#Continuous combustion, continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas gene ...
s. 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 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 thruster An azimuth thruster is a configuration of marine propellers placed in pods that can be rotated to any horizontal angle (azimuth), making a rudder redundant. These give ships better maneuverability than a fixed propeller and rudder system. Type ...
s 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 ship A double acting ship is a type of icebreaking ship designed to travel forwards 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 cond ...
s, 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.


Nuclear-powered

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 Project 22220 icebreakers to replace the aging ''Arktika'' class. The first vessel of this type entered service in 2020.


See also

* * * Resonance method of ice destruction that can be used by
hovercraft A hovercraft (: hovercraft), also known as an air-cushion vehicle or ACV, is an amphibious craft capable of travelling over land, water, mud, ice, and various other surfaces. Hovercraft use blowers to produce a large volume of air below the ...


References


External links


Gallery of Russian icebreakers

"Ice heroes"
Read a Q&A with Canadian Coast Guard acting commanding officer.
Canadian Geographic
View a Canadian Coast Guard slideshow.

Short history of Russian icebreakers by Roderick Eime
Icebreaker at the North Pole
Video of nuclear icebreaker ''Yamal'' visiting the North Pole in 2001
Book ''Polar Icebreakers in a Changing World: An Assessment of U.S. Needs'' (2007)
{{Authority control Ship types