View source for Engineering:Icebreaker

{{Short description|Ship that is able to navigate through ice-covered waters}}
[[File:120106-G-IA651-272 (6668116881).jpg|thumb|upright=1.5|USCGC ''Healy'' (WAGB-20) at right breaks ice around the Russian-flagged tanker ''Renda'', {{Convert|250|mi|km}} south of Nome, Alaska.]]
An '''icebreaker''' is a special-purpose ship or [[Engineering:Boat|boat]] designed to move and [[Earth:Ice navigation|navigate]] through [[Earth:Ice|ice]]-covered waters, and provide safe [[Earth:Waterway|waterway]]s 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 [[Engineering:Hull (watercraft)|hull]], an ice-clearing shape, and the power to push through [[Earth:Sea ice|sea ice]].<ref name="riska" />

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 ([[Engineering:Propeller|propeller]]s, [[Engineering:Drive shaft|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.<ref name="chapter5" />

== 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 in 1383 to help clear the town moat.<ref>{{cite journal |last1=de Kraker |first1=Adrian M.J. |title=Ice and water. The removal of ice on waterways in the Low Countries, 1330–1800 |journal=Water History |volume=9 |issue=2 |pages=109–128 |date=6 June 2016 |doi=10.1007/s12685-016-0152-3 |doi-access=free }}</ref><ref>{{cite news |last1=Degroot |first1=Dagomar |title=Some places flourished in the Little Ice Age. There are lessons for us now. |url=https://www.washingtonpost.com/national/health-science/some-places-flourished-in-the-little-ice-age-there-are-lessons-for-us-now/2018/02/16/455fb2d8-0c25-11e8-8b0d-891602206fb7_story.html |access-date=11 November 2019 |newspaper={{wipe|The Washington Post}} |date=19 February 2019}}</ref>  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 [[Earth:Little Ice Age|Little Ice Age]] with growing use in the [[Place:Low Countries|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, [[Earth:Ypres|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.
[[File:Amsterdam_Ice_Breaker_1733.webp|thumb|upright=1.65|Two teams of horses and a team of workers drag an ice breaker through the canals of [[Place:Amsterdam|Amsterdam]] in 1733.]]

=== 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 [[Engineering:Waterline|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.
[[File:Krsk koch.JPG|thumb|upright=1.1|
left|A 17th-century Russian [[Engineering:Koch (boat)|koch]] in a museum]]
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 [[Engineering:Paddle|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 [[Place:Greenland|Greenland]] and [[Place:Svalbard|Svalbard]] in the Arctic. [[History:Vikings|Vikings]], however, operated their ships in the waters that were ice-free for most of the year, in the conditions of the [[Earth:Medieval Warm Period|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 [[Earth:Arctic Ocean|Arctic Ocean]] became known as Pomors ("seaside settlers"). Gradually they developed a special type of small one- or two-mast wooden [[Engineering:Sailing ship|sailing ship]]s, used for voyages in the ice conditions of the Arctic seas and later on Siberian rivers. These earliest icebreakers were called [[Engineering:Koch (boat)|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 [[Earth:Portage|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.<ref>{{cite web |url=http://ris.npolar.no/documents/Seminars/Lyr/Marchenko_N.pdf |title=Navigation in ice conditions. Experience of Russian sailors |first=Nataly |last=Marchenko |website=Norsk Polarinstitutt (Svalbard Science Forum) |date=21 November 2007 |archive-url=https://web.archive.org/web/20120723205454/http://ris.npolar.no/documents/Seminars/Lyr/Marchenko_N.pdf |archive-date=2012-07-23}}</ref>

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 ''[[Engineering:Fram (ship)|Fram]]'', used by [[Biography:Fridtjof Nansen|Fridtjof Nansen]] and other great {{wipe|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.

=== Steam-powered icebreakers ===
[[File:Paddle steamer City Ice Boat n-o 1.jpg|thumb|''City Ice Boat No. 1'' at the Delaware River. The paddle steamer was built in 1837.]]
An early ship designed to operate in icy conditions<ref>{{cite web|url=https://www.theatlantic.com/technology/archive/2012/01/7-things-you-should-know-about-nuclear-powered-drone-guided-icebreakers/251514/|title=7 Things You Should Know About (Nuclear-Powered, Drone-Guided) Icebreakers |work=The Atlantic |last=Madrigal |first=Alexis C. |date=17 January 2012 |access-date=22 December 2018}}</ref> was a {{convert|51|m|ft|adj=on|abbr=out}} wooden [[Engineering:Paddle steamer|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 {{convert|250|hp|lk=in|adj=on}} steam engines and her wooden paddles were reinforced with iron coverings.<ref name="arcticportal">{{cite web |url=http://www.pame.is/images/stories/AMSA/AMSA_Background_Research_Documents/History_and_Governance_of_Arctic_Shipping/2.6-History-and-Development-of-Arctic-Marine-Technology.pdf |title=AMSA Background Research Documents: History and Development of Arctic Marine Technology er|work=The Protection of the Arctic Marine Environment Working Group (PAME) | access-date=2011-07-03}}</ref>

With a rounded shape and strong metal hull, the Russian {{ship||Pilot|icebreaker|2}} 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 [[Place:Hamburg|Hamburg]] 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,<ref>{{cite web |url=http://filologdirect.narod.ru/history/2006_04_03.pdf |title=Prolonging the navigation |first=Pavel |last=Veselov |date=1993 |number=6 |pages=36–37 |language=ru |access-date=2018-12-27 |archive-url=https://web.archive.org/web/20110816091936/http://filologdirect.narod.ru/history/2006_04_03.pdf |archive-date=2011-08-16 |url-status=dead }}</ref> ''Eisbrecher I''.<ref>{{cite book |title= Port Engineering, Volume 1: Harbor Planning, Breakwaters, and Marine Terminals |edition= 4th |last= Bruun |first=P. |isbn=0-87201-843-1 |year=1989 |publisher= Gulf Publishing Company |pages= 1375}}</ref>
[[File:Yard no. 684, Ermack. Showing the icebreaker 'Ermack' in the ice (5256788069).jpg|thumb|''Yermak'' is considered the first true modern sea-going icebreaker.]]
The first true modern sea-going icebreaker<ref>{{cite web|url=https://www.bloomberg.com/news/2011-11-14/u-s-arctic-prospects-ride-new-icebreakers-commentary-by-david-fairhall.html |url-status=dead |title=U.S. Arctic Prospects Ride on New Icebreakers | work=Bloomberg |last=Farhall |first=David |date=13 November 2011 |access-date=22 December 2018 |archive-url=https://web.archive.org/web/20131023155436/http://www.bloomberg.com/news/2011-11-14/u-s-arctic-prospects-ride-new-icebreakers-commentary-by-david-fairhall.html |archive-date=23 October 2013}}</ref> was built at the turn of the 20th century. Icebreaker {{ship||Yermak|1898 icebreaker|2}}, was built in 1899 at the [[Company:Armstrong Whitworth|Armstrong Whitworth]] naval yard in {{wipe|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-[[Engineering:Reciprocating engine|reciprocating engine]]s delivered {{convert|10,000|hp}}. 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 {{convert|80|m|adj=on}} {{ship|CGS|N.B. McLean}} (1930) and {{ship|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 [[Place:Soviet Union|Soviet Union]], 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 ships.<ref name="segercrantz" /> Reciprocating steam engines were preferred in icebreakers due to their reliability, robustness, good torque characteristics, and ability to reverse the direction of rotation quickly.<ref name="laurell">{{cite book |last= Laurell |first= Seppo |title= Höyrymurtajien aika |publisher= Gummerus Kirjapaino Oy | location = Jyväskylä |year= 1992 |isbn= 951-47-6775-6}}</ref> During the steam era, the most powerful pre-war steam-powered icebreakers had a propulsion power of about {{convert|10,000|shp|kW|abbr=out}}.<ref name="segercrantz" />
[[File:Ymer (1940) 0011-1.jpg|thumb|''Ymer'' is the world's first diesel-electric icebreaker, built in 1933.]]
The world's first diesel-electric icebreaker was the 4,330-ton Swedish icebreaker {{ship||Ymer|1933 icebreaker|2}} in 1933. At {{convert|9,000|hp|abbr=on}} divided between two propellers in the stern and one propeller in the bow, she remained the most powerful Swedish icebreaker until the commissioning of {{ship||Oden|1957 icebreaker|2}} in 1957. ''Ymer'' was followed by the Finnish {{ship||Sisu|1938 icebreaker|2}}, the first diesel-electric icebreaker in Finland, in 1939.<ref>{{cite web |url=http://www.shipgaz.com/old/magazine/issues/2003/04/oldship_0403.php |archive-url=https://archive.today/20130809053724/http://www.shipgaz.com/old/magazine/issues/2003/04/oldship_0403.php |url-status=dead |archive-date=2013-08-09 |title="Ymer": The first diesel-electric icebreaker in the world |work=Scandinavian Shipping Gazette |access-date=2013-08-09 }}</ref><ref>{{cite web|url=http://hem.passagen.se/lars.g.gustafson/Ymer1932-eng.htm|archive-url=https://web.archive.org/web/20050107171141/http://hem.passagen.se/lars.g.gustafson/Ymer1932-eng.htm|url-status=dead|archive-date=7 January 2005|title=Photo from building of Icebreaker Ymer|publisher=Passagen|access-date=5 September 2013}}</ref> Both vessels were decommissioned in the 1970s and replaced by much larger icebreakers in both countries, the 1976-built {{ship||Sisu|1976 icebreaker|2}} in Finland and the 1977-built {{ship||Ymer|1976 icebreaker|2}} in Sweden.

In 1941, the United States started building the {{sclass2|Wind|icebreaker|4}}. 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.<ref name="USCG Icebreakers">{{cite web |url=http://www.uscg.mil/history/webcutters/Icebreakers.asp |title=Icebreakers and the U.S. Coast Guard |first=Donald L. |last=Canney |website=US Coast Guard Historian's Office |publisher=United States Coast Guard |access-date=2013-01-09}}</ref><ref name="Jane's(98)">{{cite book |year=1998 |title=Jane's Fighting Ships of World War II |publisher=Crescent Books (Random House) |page=[https://archive.org/details/janesfightingshi00fran/page/308 308] |isbn=0517-67963-9 |url-access=registration |url=https://archive.org/details/janesfightingshi00fran/page/308 }}</ref><ref name="Silverstone(66)">{{cite book |last=Silverstone |first=Paul H |year=1966 |title=U.S. Warships of World War II |publisher=Doubleday and Company |page=378 }}</ref> 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 {{convert|26500|kW|hp|abbr=on}}.<ref name="segercrantz" /> In the 2020s, they will be surpassed by the new Canadian polar icebreaker, CCGS ''John G. Diefenbaker'', which will have a combined propulsion power of {{convert|36000|kW|hp|abbr=on}}.

====Canada====
[[File:LSL HalifaxHarbour.jpg|thumb|The {{ship|CCGS|Louis S. St-Laurent}} is a Canadian Coast Guard icebreaker.]]
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 {{ship|CCGS|John A. Macdonald}} 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 {{convert|15,000|hp}} was arranged in three units transmitting power equally to each of three shafts.

Canada's largest and most powerful icebreaker, the {{convert|120|m|ft|adj=on}} {{ship|CCGS|Louis S. St-Laurent}}, was delivered in 1969. Her original three steam turbine, nine generator, and three electric motor system produces {{convert|27,000|shp|lk=in}}. 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 {{USCGC|Polar Sea|WAGB-11|6}} 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 a new class of polar icebreaker for the Coast Guard.<ref>{{Cite web|url=https://www.navaltoday.com/2020/11/04/canadas-largest-icebreaker-to-undergo-life-extension-upgrade/|title=Canada's largest icebreaker to undergo life extension upgrade|date=4 November 2020}}</ref>

=== Nuclear-powered icebreakers ===
[[File:USSR 1959 pc Lenin.jpg|thumb|left|A Soviet stamp of the ''Lenin'', the world's first nuclear-powered icebreaker.]]
The second Soviet nuclear icebreaker was NS {{ship||Arktika|1972 icebreaker|2}}, the lead ship of the {{sclass|Arktika|icebreaker|4}}. In service since 1975, she was the first surface ship to reach the [[Earth:North Pole|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.<ref name="segercrantz" />

In May 2007, [[Engineering:Sea trial|sea trial]]s were completed for the nuclear-powered Russian icebreaker NS {{ship||50 Let Pobedy}}. 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.<ref>{{cite journal |url=http://www.shipsmonthly.com/auto/newsdesk/20070403154825ships.html  |title=World's largest icebreaker |journal=Ships Monthly |date=May 2007 |archive-url=https://web.archive.org/web/20090227045255/http://shipsmonthly.com/auto/newsdesk/20070403154825ships.html |archive-date=2009-02-27}}</ref>

== 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 [[Earth:Ice navigation|navigation in ice]], they are usually not powerful enough to manage the ice by themselves. For this reason, in the [[Place:Baltic Sea|Baltic Sea]], the Great Lakes and the Saint Lawrence Seaway, and along the [[Earth:Northern Sea Route|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.<ref name="segercrantz">Segercrantz, H. (1989): Icebreakers — Their Historical and Technical Development. ''Interdisciplinary Science Reviews'', Vol 14, No. 1.</ref>
[[File:Otso escorting Mirva.jpg|thumb|right|Finnish icebreaker {{ship||Otso|icebreaker|2}} escorting a merchant ship in the Baltic Sea]]
Some icebreakers are also used to support scientific research in the [[Earth:Arctic Ocean|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.<ref name="segercrantz" /> Countries such as {{wipe|Argentina}} and {{wipe|South Africa}}, which do not require icebreakers in domestic waters, have research icebreakers for carrying out studies in the polar regions.

As [[Engineering:Offshore drilling|offshore drilling]] moves to the Arctic seas, icebreaking vessels are needed to supply cargo and equipment to the drilling sites and protect the [[Engineering:Drillship|drillship]]s and [[Engineering:Oil platform|oil platform]]s from ice by performing ice management, which includes for example breaking drifting ice into smaller floes and steering [[Earth:Iceberg|iceberg]]s away from the protected object.<ref name="segercrantz" /> 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.
[[File:CGC POLAR SEA DVIDS1082500.jpg|thumb|A United States Coast Guard icebreaker in McMurdo Sound in support of Operation Deep Freeze.]]
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 [[Earth:Antarctica|Antarctic]] oceans.<ref name=":1">{{Cite book|title=Coast Guard Polar Icebreakers|last=Scott|first=Nathan|publisher=Nova Science Publishers|year=2010|isbn=978-1-60692-987-2|location=New York|pages=1–20}}</ref> Every year, a heavy icebreaker must perform Operation Deep Freeze, clearing a safe path for resupply ships to the [[Organization:National Science Foundation|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.<ref>{{Cite journal|last=Atkinson|first=Peter|date=July 2018|title=Keeping it Working|url=http://web.b.ebscohost.com/ehost/pdfviewer/pdfviewer?vid=1&sid=d0c3171c-98bd-4b98-8dea-b2ed65441a69%40sessionmgr120|journal=Sea Power Magazine|volume= 61| issue = 6|pages=26–28}}</ref>

== Characteristics ==
=== Ice resistance and hull form ===
[[File:Icebreaker Botnica 13 March 2007.jpg|thumb|The Estonian icebreaker ''Botnica'' has a typical round icebreaker bow with small stem and flare angles. The explosion-welded ice belt and "reamers" are also visible.]]
Icebreakers are often described as ships that drive their sloping bows onto the ice and break it under the weight of the ship.<ref name="turunenpartanen">{{cite book |last1=Turunen |first1=Ari |last2=Partanen |first2=Petja |title=Raakaa voimaa—Suomalaisen jäänmurtamisen tarina |trans-title=Brute force - the Finnish Icebreaking Story |language=fi |publisher=Atena Kustannus Oy |location=Jyväskylä |year=2011 |isbn=978-951-796-762-4}}</ref> 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 [[Physics:Flexural strength|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.<ref name="nrc">National Research Council (2007): [http://www.nap.edu/openbook.php?record_id=11753 Polar Icebreakers in a Changing World: An Assessment of U.S. Needs]. The National Academies Press, Washington D.C.</ref>

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|thrust]] from the propellers equals the combined hydrodynamic and ice resistance of the vessel.<ref name="riska">{{cite web |last=Riska |first=K |title=Design of Ice Breaking Ships |url=http://www.eolss.net/Sample-Chapters/C05/E6-178-45-00.pdf |access-date=2012-10-27 |website=[[Biology:Encyclopedia of Life Support Systems|Encyclopedia of Life Support Systems]] (EOLSS)}}</ref> An alternative means to determine the icebreaking capability of a vessel in different ice conditions such as [[Earth:Pressure ridge (ice)|pressure ridges]] is to perform [[Ship model basin|model tests]] in an [[Ice tank|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 [[Engineering:Flare (ship)|flare]] at the waterline is as small as possible. As a result, icebreaking ships are characterized by a sloping or rounded [[Engineering:Stem (ship)|stem]] as well as sloping sides and a short parallel midship to improve maneuverability in ice.<ref name="nrc" /> However, the spoon-shaped bow and round hull have poor hydrodynamic efficiency and [[Engineering:Seakeeping|seakeeping]] characteristics, and make the icebreaker susceptible to [[Engineering:Slamming|slamming]], or the impacting of the bottom structure of the ship onto the sea surface.<ref name="riska" /> 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.<ref name="segercrantz" />
[[File:Swedish icebreaker Oden.jpg|thumb|The Swedish icebreaker ''Oden'' is built with a flat bow and a water deluge system designed to reduce friction between the hull and ice.]]
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 [[Engineering:Explosion welding|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.<ref name="segercrantz" />

=== 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.<ref name="chapter5">[http://www.ccg-gcc.gc.ca/Icebreaking/Ice-Navigation-Canadian-Waters/Ship-Design Chapter 5 Ship Design and Construction for Ice Operations]. Canadian Coast Guard. {{retrieved|access-date=2013-08-20}}</ref>
[[File:Eisbrecher - panoramio.jpg|thumb|left|Bow of the {{RV|Polarstern}}, a research icebreaker. The bow of an icebreaker is usually the most reinforced area of the ship.]]
Short and stubby icebreakers are generally built using transverse framing in which the shell plating is stiffened with frames placed about {{convert|400|to|1000|mm|ft|0}} apart as opposed to [[Engineering:Longitudinal framing|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.<ref name="chapter5" /> While the shell plating, which is in direct contact with the ice, can be up to {{convert|50|mm|in}} thick in older polar icebreakers, the use of high strength steel with yield strength up to {{convert|500|MPa|psi|abbr=on}} 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.<ref name="chapter5" /><ref>Norden, R. (1989): Extra high strength structural steels for ice breakers. Proceedings of the 10th International Conference on Port and Ocean Engineering under Arctic Conditions (POAC'89), Volume 2, page 839.</ref>

If built according to the rules set by a classification society such as [[Organization:American Bureau of Shipping|American Bureau of Shipping]], Det Norske Veritas or Lloyd's Register, icebreakers may be assigned an [[Engineering:Ice class|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 [[Engineering:Polar Class|Polar Class]] (PC) to replace classification society specific ice class notations.

=== Power and propulsion ===
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 [[Physics:Direct current|direct current]] (DC) generators and propulsion motors, but over the years the technology advanced first to [[Physics:Alternating current|alternating current]] (AC) generators and finally to frequency-controlled AC-AC systems.<ref name="segercrantz" /> 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 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.<ref name="segercrantz" />

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.<ref name="segercrantz" />

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 [[Engineering:Gas turbine|gas turbine]]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.<ref name="segercrantz" /> The diesel-electric power plant can produce up to {{convert|18000|hp|kW|abbr=on|order=flip}} while the gas turbines have a continuous combined rating of {{convert|60000|hp|kW|abbr=on|order=flip}}.<ref>[http://www.uscg.mil/pacarea/cgcpolarstar/history.asp CGC Polar Star History]. United States Coast Guard. {{retrieved|access-date=2013-08-24}}</ref>
[[File:Coast Guard Healy leaves dry dock (26142269466).jpg|thumb|View of the underside of {{USCGC|Healy|WAGB-20|6}} hull and propellers.]]
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 [[Engineering:River icebreaker|river icebreaker]]s have been built with four propellers in the stern. [[Engineering:Ducted propeller|Nozzles]] may be used to increase the thrust at lower speeds, but they may become clogged by ice.<ref name="segercrantz" /> Until the 1980s, icebreakers operating regularly in [[Earth:Pressure ridge (ice)|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.<ref name="art fleet">{{cite web |title=Arctia Fleet |url= http://www.arctia.fi/fleet |website=Arctia Shipping |access-date=2013-01-11}}</ref>

[[Engineering:Azimuth thruster|Azimuth thruster]]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 [[Engineering:Double acting ship|double acting ship]]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 [[Engineering:Oblique icebreaker|icebreakers that operate sideways]] to open a wide channel through ice.

====Nuclear-powered====
[[File:Аппаратная.jpg|thumb|Reactor head for the ''Yamal'', a nuclear-powered icebreaker.]]
The steam-powered icebreakers were resurrected in the late 1950s when the Soviet Union commissioned the first [[Engineering:Nuclear-powered icebreaker|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 {{convert|60000|kW|hp|abbr=on}} icebreakers to replace the aging ''Arktika'' class. The first vessel of this type entered service in 2020.

===Resonance method===
{{main|Earth:Resonance method of ice destruction}}
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.<ref>{{cite web|url=http://www.griffonhoverwork.com/news/latest-news/ice-breaking-hovercraft.aspx|title=Canadian Coast Guard Ice Breaking hovercraft|website=www.griffonhoverwork.com|access-date=2017-02-06|archive-url=https://web.archive.org/web/20170207031703/http://www.griffonhoverwork.com/news/latest-news/ice-breaking-hovercraft.aspx|archive-date=2017-02-07|url-status=dead}}</ref>

== See also ==
* {{annotated link|Engineering:Double acting ship}}
* {{annotated link|Engineering:Ice class}}
* {{slink|List of auxiliaries of the United States Navy#Icebreakers (AGB)}}
* {{annotated link|Engineering:Nuclear-powered icebreaker}}
* {{annotated link|Engineering:Polar Class}}
* {{annotated link|Engineering:River icebreaker}}

== References ==
{{Reflist|33em}}

== External links ==
* [http://englishrussia.com/?p=1838 Gallery of Russian icebreakers]
* [https://web.archive.org/web/20060414053608/http://www.canadiangeographic.ca/magazine/MA06/indepth/people.asp "Ice heroes"]: Read a Q&A with Canadian Coast Guard acting commanding officer.
* [https://web.archive.org/web/20060414053608/http://www.canadiangeographic.ca/magazine/MA06/indepth/people.asp Canadian Geographic]: View a Canadian Coast Guard slideshow.
* [http://www.travelnorthpole.com/2010/06/icebreakers-pushing-limits.html Pushing the Limits] Short history of Russian icebreakers by Roderick Eime
* [https://www.youtube.com/watch?v=x1XMZTzELaE Icebreaker at the North Pole]: Video of nuclear icebreaker ''Yamal'' visiting the North Pole in 2001
* [http://books.nap.edu/openbook.php?record_id=11753&page=R1 Book ''Polar Icebreakers in a Changing World: An Assessment of U.S. Needs'' (2007)]

{{ModernMerchantShipTypes}}


[[Category:Ship types]]

{{Sourceattribution|Icebreaker}}