Icebreaker - Definition


Icebreaker - Definition

For other uses, see Icebreaker (disambiguation).

US Coast Guard icebreakers near , February 2002

US Coast Guard icebreakers near McMurdo Station, February 2002

An icebreaker is a special purpose ship designed to move through ice covered marine environments. 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. The specially designed hull causes the broken ice to be pushed out of the way thus allowing the icebreaker to proceed forward. An icebreaker needs a specially strengthened hull 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 sustain enough damage to require major repairs or to sink her. Ice will easily hole a non-strengthened ship. This result was graphically displayed in the sinking of the RMS Titanic.

Contents

1 History

2 Function of icebreakers

3 Future of Icebreakers

4 Some icebreakers

4.1 Argentina
4.2 Australia
4.3 Canada
4.4 Finland
4.5 Germany
4.6 International
4.7 Japan
4.8 Russia
4.9 Sweden
4.10 United States

History

Even in 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. 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, in case the ship was "nipped" by the ice. Nipped describes the event when ice floes around a ship are push 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.

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 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.

Future of Icebreakers

The shape which allows icebreakers to move through ice also make the ship uncomfortable in open water and have poor fuel effiency.

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 with the round; sled-like bow used to ride up on the ice; tend to slam into waves and 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 removes the need for rudders. Azipods also allow a ship to travel backwards as easily as it travels forward. The double acting icebreaker is unique beacuse 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 drives backward through the ice.