An icebreaker is a special purpose ship designed to move and navigate through ice covered marine environments.
For a ship to be considered an icebreaker it requires three components, an ice strengthened hull, an ice clearing shape, and the power to push through. An ordinary ship with no strengthening will not risk touching ice at all, no matter how gently. An icebreaker needs a specially strengthened hull to work in ice conditions. These ships break ice by using their momentum and power to push the bow up on the ice. The weight of the ship causes the ice to be pushed down which in turn causes the ice to split and break off in chunks. An icebreaker's specially designed hull must direct the ice around the vessel or under the ice to allow the icebreaker to proceed forward. A buildup of broken ice will stop a vessel much faster than breaking the ice itself. At a greater risk of damage from ice is a ship's propulsion system. Essential to an icebreaking vessel is the ability to propel itself onto the ice, breaking it, and then successfully clearing the ice debris from its path.
Even in the 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 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. Nipped describes the event 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 transmitted through ice formations that, although many miles distant, transmit the pressure.
At the beginning of the 20th Century several 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 tonnes displacement. Several technological advances were introduced over the years, but it was not until the introduction of nuclear power (icebreaker Lenin, 1959) that icebreakers developed their full potentials.
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, or is a nuclear powered icebreaker. 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 caused by banging against the ice.
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 water bubbles, all designed to allow an icebreaker stuck amidst thick ice to break free. Many icebreakers also carry aircraft (formerly seaplanes and now helicopters) to assist in reconnaissance and liaison.
The shape which allows icebreakers to move through ice also makes them uncomfortable in open water and means they have poor fuel efficiency.
Icebreakers tend to roll side to side causing discomfort to the crew. Some new icebrakers such as the USCGC Healy make use of roll tanks. Roll tanks use computer controlled pumps to rapidly shift ballast water side to side to keep the vessel upright.
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 bow to cut through waves and help prevent waves from slamming the bow of the ship. Icebreakers have a round sled-like bow, however; they tend to slam into waves, which can be a risk 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, ship docking, and remove the need for rudders. Azipods also allow a ship to travel backwards as easily as it travels forwards. The double acting icebreaker is unique because its stern is shaped like an icebreaker's bow. Normally travelling forward, 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.
Canadian Coast Guard
- MV Caribou (Gulfspan ferry)
- MV Joseph and Clara Smallwood (Gulfspan ferry)
Finnish Maritime Administration
Last updated: 05-07-2005 10:05:34
Last updated: 05-13-2005 07:56:04