Why are ice classes needed?

the Ship Classification Societies "ice class" has a fundamental basis on the safety of the ship hull and the essential propulsion machinery. The class defines sufficient installed power for a safe operation in ice covered waters. The classification also defines certain hull structure against certain level ice, which in the Baltic Sea conditions is defined using the first year ice definition. The classifications also defines the requirements for the propeller shaft as a minimum power for maintaining ship speed in a re-frozen (covered by e.g. brash ice) fairway navigation channel.

When the ice conditions became difficult, traffic restricions are imposed. The restrictions pertain to the availability of icebreaker assistance. Some of the restrictions are about safety independent of assistance standards; some are caused by the availability of icebreaker services. The traffic restrictions are based on Ice Class Rules.