While the Arctic is warming at twice the rate of the rest of the planet, ice conditions there as well as on northern seas and lakes will require icebreakers for many years to come. The same will be true for the high latitudes of the Southern Hemisphere.
The icebreaking ship has basically a very strong hull with the largest possible engines to power her through ice. Historically her primary function has been to keep shipping lanes open for as long as possible. In recent times these ships have been increasingly needed, however, as platforms for polar research activities and resource development—all functions often at odds with the vessels' primary mission.
Development of the seagoing steam engine and screw propulsion in the mid-1800s made possible the first practical icebreakers. The ships worked by virtue of brute force pushing against or ramming the ice. This limited the thickness of ice that could be broken; hitting it head on is where ice is strongest. The substance is relatively weak if it is pushed down or lifted up.
To take advantage of this, early designs used a curved bow that would ride up on the ice sheet, allowing the weight of the ship to crush down on it. Later, larger icebreakers were fitted with a steel "ice knife" in the stem that fractured the ice. In addition, to avoid being trapped, larger ships have the ability to wallow. They can move large quantities of water from side to side as well as fore and aft to weaken the surrounding ice. Special hull coatings also help reduce friction between ship and ice. Some ships have air bubbling systems that flow large quantities of air through small openings in the forward part of the hull. Air injected into the water floats up beneath the ice, further weakening it.
The icebreakers' propellers have to be very robust. Their massive screws generally are made of stainless steel with replaceable blades. The ship's propeller helps the breaker work by milling the ice, breaking up larger chunks that pass astern. This often results in damage, so icebreakers carry a supply of spare blades.
Icebreakers are operated by 15 nations, with Finland, Russia, and Canada having the largest fleets. Finland, as the leading builder of these ships, has constructed most of the Russian non-nuclear icebreakers.
The most powerful breakers are the six (four still in service) Russian nuclear-powered Arktika-class ships. With a displacement of 25,000 tons and 75,000 horsepower from two reactors, these triple-screw ships can break through 9.2 feet of ice at a steady three knots. Five of them have the curved bow, ice knife, heeling and trim tanks, and air bubbling system. The most recent ship, 50 Lyet Pobyedi (50 Years of Victory), joined the fleet in 2007. Under construction since the late 1980s, she has several new features including a more efficient spoon-shaped bow.
The Coast Guard's Polar Star (WAGB-10), built in 1976, and the 1978-completed Polar Sea (WAGB-11) are the United States' most powerful icebreakers. Using a combination of diesel engines and gas turbines that produce 60,000 horsepower, they can continuously break ice up to 6 feet thick. Both are showing their age and will have to be taken out of service in the next few years. The Polar Star is already in standby status and would require shipyard work to become active. Presently there are no firm plans to replace the ships.
Three years ago, the Coast Guard put a new icebreaker, the Healy (WAGB-20), into service. Not quite as strong as the Polar-class, the Healy has 30,000 horsepower and can continuously work ice up to 4.5 feet thick. The Coast Guard also has a few smaller icebreaking vessels for use on the Great Lakes where winter ice shortens the navigation season.
In addition to icebreakers there are ice-strengthened vessels. Their hull plating is thicker and frame spacing closer together than conventional ships of the same size. The top group of these vessels can safely operate in ice up to about 2 feet thick. They do not break ice per se but can navigate through most first-year sea ice. For thicker, harder multiyear ice, they still require assistance of icebreakers.
Icebreakers are very expensive ships to build and operate. They are increasingly supporting offshore operations (e.g., seafloor hydrocarbons and mining) as well as scientific research. Few of the older vessels are adequately configured for this work, however the Healy, Germany's Polarstern, and Sweden's Oden all have significant support capabilities for polar research. Also the U.S. National Science Foundation has long-term charters for two ice-strengthened ships, the Nathaniel B. Palmer and Lawrence M. Gould, which are dedicated to polar research tasks.