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Ice navigation is a specialist area ofnavigation involving the use of maritime skills to determine and monitor the position ofships in cold waters, whereice is a hazard to the safety of navigation.[1] The presence ofsea ice requires a ship to exercise caution, for example by avoidingicebergs, slowly sailing through alead, or by working with anicebreaker to follow a course through the ice to a destination.[2] Additionally ships must also deal with the extreme cold of the climate in regions such as thepoles; this involves removal of ice accumulation from the ship, as well as protecting thecrew from the elements while working on the deck.[3] Ships and their crews operating in ice will follow established rules ofseamanship, as well as complying with national and international regulations such as thePolar Code.
Ice strengthened vessels are typically used for navigation in ice regions, where additional hull strengthening and other design elements ensure operation in areas of high ice concentration.[4]
Ice navigation occurs wherever a waterborne vessel transits throughsea ice. One of the more common regions for ice navigation is theBaltic Sea, where vessels visiting theBaltic States will make their way throughfirst year ice in thewinter months, often with anicebreaker, or with ice reports, charts and data provided by meteorological offices.[5][6] Other areas include theArctic Ocean, where increasing numbers of ships are transiting the region in the summer months forcruising and to transport cargo, as a result ofoil andgas extraction in areas such asYamal.[7] The problems of increased shipping inpolar regions presents additional challenges, including maritime safety concerns in the event that ice navigation is not carried out carefully.[7] Ships will also pass through ice when navigating in theAntarctic, although most ships are eitherresearch vessels orcruise ships that have been especially ice strengthened. Other significant maritime regions where ships will navigate through Ice include theSaint Lawrence Seaway, aroundGreenland and the Canadian coast, theNorth Atlantic during iceberg season and through theNorthwest Passage.[8]
The accumulation of ice on thesuperstructure is a dangerous phenomenon. When the temperature is below −2.2 °C (28.0 °F) slight icing will occur at winds of 5 Bft, moderate icing at 7 Bft, and severe icing at 8 Bft. When sailing in fresh water, icing will occur from 0 °C (32 °F) and below. The more common causes of ice formation on the superstructure are from spray by wave crests and ship-generated spray. Other possibilities are snow fall, sea fog, a drastic fall in ambient temperature and also freezing raindrops in contact with the cold steel. The heading of the vessel relative to the wind and seas will determine which parts of the superstructure will ice first. Icing can immobilise equipment such as anchors or cause a dangerous list if the windward side of the vessel ices more heavily.
Aradar can be useful in detecting ice, but the returning signal which bounces off ice (even icebergs) is very faint, much lower than from ships. Conventional marine radars are designed for target detection and avoidance. Enhanced marine radars provide a higher definition image of the ice that the vessel is transmitting and will result in a much clearer image. This image can be used to identify the quantity and sort of ice that has to be dealt with. In standard radar, sea clutter affects the ability to see in the near vicinity of the vessel. AnX-band radar set to a short pulse can give improved results.[9]