Icebreaker Kapitan Khlebnikov In The Ross Sea, Antarctica From Helicopter

An icebreaker is a special-purpose ship or boat designed to move and navigate through ice-covered waters, and provide safe waterways for other boats and ships. Although the term usually refers to ice-breaking ships, it may also refer to smaller vessels, such as the icebreaking boats that were once used on the canals of the United Kingdom.

For a ship to be considered an icebreaker, it requires three traits most normal ships lack: a strengthened hull, an ice-clearing shape, and the power to push through sea ice.

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 (propellers, 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 Belgium town of Bruges 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 with growing use in the Low Country where significant amounts of trade, and transport of people and goods took place. In the course of fifteenth century the use of ice breakers in Flanders (Oudenaarde, Kortrijk, Leper, 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.

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 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 indigenous Arctic people. Their kayaks are small human-powered boats with a covered deck, and one or more cockpits, each seating one paddler who strokes a single or double-bladed paddle. Such boats have no icebreaking capabilities, but they are light and well fit to carry over the ice.

In the 9th and 10th centuries, the Viking expansion reached the North Atlantic, and eventually Greenland and Svalbard in the Arctic. Vikings, however, operated their ships in the waters that were ice-free for most of the year, in the conditions of the Medieval Warm Period.

In the 11th century, in North-Russia the coasts of the White Sea, named so for being ice-covered for over half of a year, started being settled. The mixed ethnic group of the Karelians and the Russians in the North-Russia that lived on the shores of the Arctic Ocean became known as Pomors ("seaside settlers"). Gradually they developed a special type of small one- or two-mast wooden sailing ships, used for voyages in the ice conditions of the Arctic seas and later on Siberian rivers. These earliest icebreakers were called kochi. The koch's hull was protected by a belt of ice-floe resistant flush skin-planking along the variable water-line, and had a false keel for on-ice portage. If a koch became squeezed by the ice-fields, its rounded bodylines below the water-line would allow for the ship to be pushed up out of the water and onto the ice with no damage.

In the 19th century, similar protective measures were adopted to modern steam-powered icebreakers. Some notable sailing ships in the end of the Age of Sail also featured the egg-shaped form like that of Pomor boats, for example the ''Fram'', used by Fridtjof Nansen and other great Norwegian Polar explorers. ''Fram'' was the wooden ship to have sailed farthest north (85°57'N) and farthest south (78°41'S), and one of the strongest wooden ships ever built.

Steam-powered icebreakers

An early ship designed to operate in icy conditions was a wooden paddle steamer, ''City Ice Boat No. 1'', that was built for the city of Philadelphia by Vandusen & Birelyn in 1837. The ship was powered by two steam engines and her wooden paddles were reinforced with iron coverings.

With a rounded shape and strong metal hull, the Russian of 1864 was an important predecessor of modern icebreakers with propellers. The ship was built on the orders of merchant and shipbuilder Mikhail Britnev

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