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Icebreakers and ice strengthened ships

Antarctic Ships: Overview Historical: L'Astrolabe & Zelee | Aurora | Belgica | Discovery | Endurance | Erebus and Terror | Fram page2 | Nimrod | Terra Nova    Modern: Ice-strengthened and icebreakers | James Clark Ross | Kapitan Khlebnikov | Yamal

Ships then and now - a comparison

Nathaniel B. Palmer, US icebreaker, picture courtesy NSFIn the very earliest days of polar exploration, ice-strengthened ships were used. These were originally wooden and based on existing designs, but beefed up. Particularly around the waterline with double planking to the hull, strengthening cross members inside the ship and bands of iron around the outside and / or metal sheeting at the bows, stern and along the keel.

Such strengthening was designed to help the ship push through ice and also in case the ship was "nipped" by the ice. Nipped is an innocuous sounding word to describe a terrible and powerful event when ice floes around a ship driven by winds and tides (often many miles distant) push against the ship trapping it as if in a vice and causing damage - often damage enough to reduce the ship to match-wood.

Such damage might be repairable, it might cause the loss of the ship when the ice finally relented - the ship now no longer being able to float as happened to Shackleton's Endurance or it might cause the loss of the ship in as little as 15 minutes from first pressure being exerted. In the days of wooden ships, the only vessel that could survive such treatment was the Fram, built for Fridtjof Nansen. The Fram was prodigiously strong, but it's chief defence was that when squeezed from the sides it would respond by rising up due to a very rounded hull shape. Even the mighty Fram at one point looked to be be in danger when ice floes built up to such an extent that they might fall on it and prevent it rising when squeezed.

US icebreaker escorting a supply ships through an open channel filled with loose "brash" ice, phot use courtesy NSFThese days, ships that go to the polar regions are of course no longer made of wood, but of steel. They still need to be specially strengthened to work in ice conditions. An ordinary ship with no strengthening will not risk touching ice at all, no matter how gently. A modern ship weighing thousands of tonnes meeting an iceberg weighing perhaps as much again or up to thousands of times more can easily sustain enough damage to require major repairs or to sink her. Ice will easily hole a non-strengthened ship.

Ships therefore that have any chance of contacting ice are at least ice-strengthened if not being designed to plough through the ice as do ice-breakers.

Icebreakers are needed if there is a trade route to keep ice free, if there are military reasons for patrolling in areas with heavy sea ice or if you need to work in heavy ice condition, particularly in winter. Icebreakers are expensive to build, very expensive to run (often powered by gas turbines or a nuclear generator). They are uncomfortable to travel in on the open sea, all ships designed for the ice have rounded keels with no protuberances for stability and roll heavily in a even a light sea - and icebreakers are designed for the ice more than any other kind of ship. They are also uncomfortable to travel in when breaking through continuous thick ice due to constant vibration and jarring against the ice and the noise that it makes.

Icebreakers are therefore generally owned by those countries with an interest in the north-east and north-west passages in the Arctic.

Ice strengthening on the other hand is found much more commonly in ships designed for Arctic or Antarctic work. There is no actual universal definition of what needs to be done to a ship to be "officially ice strengthened" and it can be applied to all manner of ships, whether supply ships, tankers, container ships, warships etc. Commonly ice-strengthened ships can cope with continuous one year old ice about 50cm - 100cm thick.

Breaking ice by any ship is not a case of forcing the ice aside as is often assumed, but occurs by the ship riding up and over the ice in front of it, with the weight of the ship then breaking the ice.

James Clark Ross, British Antarctic Survey ice strengthened ship, picture courtesy BAS

Characteristics of ice-strengthened ships

Most of the ships that supply Antarctic bases are ice strengthened rather than full blown ice breakers

bulletDouble hull, with a gap between them, the gap may be air or filled with water ballast. If the outer hull is punctured the inner will hopefully not be.
bulletFlat hull shape with a rounded rather than pointed bow. This allows the front of the ship to drive forwards, rise above the ice and then let the weight of the ship break the ice.
bulletSpecially formulated hull polymer paints for strength and also low friction when in contact with ice.
bulletSpecial engine cooling arrangements so that the inlet for water taken on board to cool the engine doesn't get blocked with ice - likewise the water outlet.
bulletNo stabilizers or any other kind of hull protuberance that might get ripped off by ice
bulletHelicopter, for scientific work, but also for spotting leads and open water in the ice to guide the ship.
bulletRudder and propeller protected by the shape of the hull, so that ice moving backwards is less likely to cause damage.
bulletThicker than normal steel, particularly at the bow and at the level of the water-line
bulletReinforced "ice belt" that typically extends about 1m above and below the water line. This is where the hull has thicker steel and also has extra internal ribs to help the stiffening. These are usually twice as many of these ribs than in a comparable "normal" ship.
bulletPowerful bow and stern thrusters to help manoeuvring in tight spaces such as pack ice.

 

Kapitan Khlebnikov, Russian icebreaker

Characteristics of Ice Breakers

Ice breakers have the features of ice strengthened ships and then some of their own too

bulletHeavy for their size, to make them more effective at breaking through ice when they are pushed up above it by their engines.
bulletVery gradual upwards slope at the bow, particularly at the water line to allow the bow to ride up over ice before the weight breaks through.
bulletHull made from special steels designed for optimum strength at low temperatures
bulletExtra thick steel at the bow, the stern and at the waterline.
bulletAn "ice horn" to protect the rudder and propeller when in reverse, and an "ice knife" in front to protect it when in forwards motion.
bulletElectric propulsion to the propellers. Electric motors can apply torque when not actually turning or when only turning slowly, so hitting a large piece of ice will not stop the engine.
bulletExtra strong propellers with replaceable blades. There may also be a propeller inspection well to examine them in operation and the facility to change blades while at sea.
bulletVery powerful engines. The engine may be diesel possibly with extra power supplied by gas turbines for ice breaking or be nuclear powered.
bulletAir bubbling systems to assist ice-breaking. Air is forced under pressure from 2m or so below the water line where ice is met, helping to break it and move it out of the way.
bulletHeated water jets below the waterline to help when breaking through ice.
bulletAbility to rapidly move large amounts of water ballast within the ship to shift the weight when needing to break ice.
bulletHull divided by bulkheads into a series of watertight compartments in case the hull is holed.
bulletPowerful searchlights for use in dark winter conditions.

The Kapitan Khlebnikov icebreaker | Yamal, a nuclear powered icebreaker

 


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