An icebreaker is a special-purpose ship or boat designed to move and navigate through ice-covered waters. Although the term usually refers to icebreaking ships, it may also refer to smaller vessels (e.g., icebreaking boats that were used on the canals of Great Britain in the days of commercial carrying).
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 ice-covered waters.
To pass through ice-covered water, an icebreaker uses its great momentum and power to drive its bow up onto the ice, breaking the ice under the immense weight of the ship. Because a buildup of broken ice in front of a ship can slow it down much more than the breaking of the ice itself, the speed of the ship is increased by having a specially designed hull to direct the broken ice around or under the vessel. The external components of the ship's propulsion system (propellers, propeller shafts, etc.) are at even greater risk of damage than the vessel's hull, so the ability for an icebreaker to propel itself onto the ice, break it, and clear the debris from its path successfully is essential for its safety.
Sailing ships in the polar waters
Even in the earliest days of polar exploration, ice-strengthened ships were used. 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, 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. Although such wind and tidal forces may be exerted many miles away, the ice transmits the force.
The first boats to be used in the polar waters were that of the indigenous Arctic people. The kayak is the most famous type of a small human-powered boat with a covered deck, and one or more cockpits, each seating one paddler who strokes a double-bladed paddle. Such boats, of course, 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 the most part of the year, in the conditions of the Medieval Warm Period.
In the 11th century Russians started settling the coasts of the White Sea, named so for being ice-covered for over half of a year. The ethnic subgroup of Russians 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 kochs. Koch's hull was protected by a belt of ice-floe resistant flush skin-planking (made of oak or larch) 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 alike that of Pomor boats, for example the famous Fram, used by Fridtjof Nansen and other great Norwegian Polar explorers. Fram is said to be the wooden ship to have sailed farthest north (85°57'N) and farthest south (78°41'S), and perhaps the strongest wooden ship ever built.
The first steam-powered icebreaking boat was the City Ice Boat No. 1, built by the city of Philadelphia in 1837. She was a wooden paddle steamer intended to break ice in the harbor. This ice-clearing boat relied mainly on the strengthened hull and the power of the engine.
The first European steam-powered icebreaker, as well as the first metal-hull icebreaker was the Russian Pilot, built in 1864 on orders of merchant and shipbuilder Mikhail Britnev. It had the bow altered to achieve an ice-clearing capability (20° raise from keel line). This allowed the Pilot to push itself 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 1864-1890 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 the Pilot, Mikhail Britnev built a second similar vessel "Boy" ("Battle" in Russian) in 1875 and a third "Booy" ("Buoy" in Russian) in 1889.
The cold winter of 1870-1871 led to the international recognition of Britnev's design. That year the Elbe River and the port of Hamburg freezed, which caused a prolonged halt of navigation and huge commercial losses. In such circumstances, Germans purchased the Pilot's design from Britnev for some 300 rubles. Thus the German Eisbrecher I appeared in 1871, and other European countries soon followed the suit.
With its rounded shape and strong metal hull, Pilot had all the main features present in the modern icebreakers, and that's why it is often considered the first true icebreaker. Another contender for this title is icebreaker Yermak, built in England for Russia according to the design of Admiral Stepan Makarov and under his supervision. Makarov borrowed the main principles from Pilot and applied them for creation of the first polar icebreaker, which was able to run over and crush pack ice. Between 1899-1911 Yermak sailed in heavy ice conditions for more than 1000 days.
At the beginning of the 20th century, several other countries began to operate purpose-built icebreakers. Most were coastal icebreakers, but Russia, and later, the Soviet Union, also built several oceangoing icebreakers of around 10,000 ton displacement, eventually converting to diesel engine propulsion.
Several technological advances were introduced into icebreaking technology over the years, but it was not until the introduction of nuclear power in the Soviet icebreaker Lenin in 1959 that icebreakers developed their full potential. NS Lenin was launched in 1957 and completed in 1959. It was both the world's first nuclear powered surface ship and the first nuclear powered civilian vessel. Lenin was put into operation in 1959 and officially decommissioned in 1989.
In May 2007, sea trials were completed for the nuclear-powered Russian ice-breaker NS 50 Years Since Victory (Russian: 50 лет Победы, transliterated as 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 (now St Petersburg), and the ship was launched in 1993 as the NS Ural. This icebreaker was intended to be the sixth and last of the Arktika class, and currently is the world's largest icebreaker.
Function of icebreakers
Icebreakers are needed to keep trade routes open where there are either seasonal or permanent ice conditions. Icebreakers are expensive to build and very expensive to run, whether the icebreaker is powered by gas turbines, diesel-electric powerplant or nuclear energy. They are uncomfortable to travel in on the open sea: almost all of them have thick, rounded keels, and with no protuberances for stability, they can roll even in light seas. They are also uncomfortable to travel in when breaking through continuous thick ice due to constant motion, noise, and vibration.
A modern icebreaker typically has shielded propellers both at the bow and at the stern, as well as side thrusters; pumps to move water ballast from side to side; and holes on the hull below the waterline to eject air bubbles, all designed to allow an icebreaker stuck amidst thick ice to break free. Many icebreakers also carry aircraft (formerly seaplanes but now helicopters) to assist in reconnaissance and liaison.
Design and construction
Icebreakers are constructed with a double hull and watertight compartments in case of a breach. The ship's hull is thicker than normal, especially at the bow, stern, and waterline, using special steel that has optimum performance at low temperatures. The thicker steel at the waterline typically extends about 1 m above and below the waterline and is reinforced with extra internal ribbing, sometimes twice the ribbing of a normal ship. The bow is rounded rather than pointed, allowing the vessel to ride up over the ice, breaking it with the weight of the vessel. The hull has no appendages likely to be damaged by the ice, and the rudder and propeller are protected by the shape of the hull. The propeller blades are strengthened, and the vessel has the ability to inspect and replace blades while at sea.
The optimal shape for moving through ice makes icebreakers uncomfortable in open water and gives them poor fuel efficiency.
In open-water travel, icebreakers tend to roll side to side to the discomfort of the crew. Some new icebreakers, such as the USCGC Healy, make use of anti-roll tanks. Anti-roll tanks are incompletely filled ballast tanks which span the beam of the vessel. Ballast water in these tanks is allowed to move side to side, or slosh, as a free surface. Retarding baffles inside the anti-roll tank slow the side-to-side flow of water. By varying the water level inside the anti-roll tank, the natural frequency of the slosh is used to counteract the rolling of the vessel. Anti-roll tanks by their nature decrease a ship's stability and must always be used with caution. Use of computer-controlled valves allow for better control of these anti-roll tanks.
A greater concern is how well a ship cuts through waves. The ability of a ship to cut through waves can greatly affect its fuel efficiency and even its safety in a storm. Most ships use a sharp or bulbous bow to cut through waves and help prevent waves from slamming the bow of the ship. However, icebreakers have a round sled-like bow. They tend to slam into waves, which can be risky in high seas.
Recent advances in ship propulsion have produced new experimental icebreakers. Electrically driven propellers are mounted to steerable pods under the ship. These Azimuthing Podded Propulsors, or Azi-pods, improve fuel efficiency, ship steering, and ship docking and remove the need for rudders. Azipods also allow a ship to travel backwards as easily as it travels forwards; this allows double acting icebreakers, a type of unique merchant ship where the stern is shaped like an icebreaker's bow. Traveling forward normally, a double acting icebreaker uses a conventional ship bow for a more comfortable ride. When ice is encountered, the ship turns around and travels backwards through the ice. The MT Mastera and MT Tempera are two vessels using this new technology.
In the 1980s, hovercraft were shown to be effective as icebreakers on rivers. Instead of displacing or crushing the ice from above, they work by injecting a bubble of air under the ice sheet, causing it to break off under its own weight and be swept downstream by the current. The purpose is usually not to provide navigation channels but rather to prevent ice dams from forming and causing local flooding.
2014 will see the introduction of the first Ice Catcher vessel from Russian Steel company Lakursk. Full beam turrets capture the ice (upwards of 10m) which the vessels use to cool anti-generator propulsion engines at a 5/2 ratio. Norwegian Shipping Incoporated have developed a similar Ice Capture prototype shceduled for delivery 2019 (Ougzhan Shipyard, China).
- Navigation in ice conditions. Experience of Russian sailors by Nataly Marchenko at ris.npolar.no (Svalbard Science Forum)
- Prolonging the navigation by Pavel Veselov. 1993. № 6. pp. 36-37. (Russian)
- Bruun P (1989). Port Engineering, Volume 1: Harbor Planning, Breakwaters, and Marine Terminals (4th ed. ed.). Gulf Publishing Company. pp. 1375. ISBN 0872018431.
- "World's largest icebreaker," Ships Monthly. May 2007.
- "Icebreakers and ice strengthened ships". http://www.coolantarctica.com/Antarctica%20fact%20file/ships/icebreaker.htm. Retrieved 2007-11-25.
- 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.
- Pushing the Limits 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)
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