Icebreaker

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

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 vice and causing damage. This vice 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. All ships designed for the ice have rounded keels and with no protuberances for stability they roll heavily in a even a light sea. They are also uncomfortable to travel in when breaking through continuous thick ice due to constant noise and vibration caused by jarring against the ice.