Is Ice Class the same as Ice Category?

As a follow on from the posts on the Polar Code here is a quick guide to Ice Class and Category.Sea ice

Polar Class and Ice Category Compared

Polar class, sometimes referred to as ‘Ice class’ is a Classification Society designation, whilst Ice Category is a IMO Polar Code designation.

What is Polar Class?

The Unified Requirements for Polar Class ships apply to ships constructed of steel and intended for independent navigation in ice-infested polar waters

Click here for IACS unified requirements>

What are the Polar Class descriptions?

These are based on WMO Sea Ice Nomenclature.

  • 1: Year-round operation in all polar waters
  • 2: Year-round operation in moderate multi-year ice conditions
  • 3:Year-round operation in second-year ice which may include multiyear ice inclusions
  • 4: Year-round operation in thick first-year ice which may include old ice inclusions
  • 5: Year-round operation in medium first-year ice which may include old ice inclusions
  • 6: Summer/Autumn operation in medium first-year ice which may include old ice inclusions
  • 7: Summer/Autumn operation in thin first-year ice which may include old ice inclusions

What are the Ice Categories?

  • Category A ship: A ship designed for operation in polar waters in at least medium first-year ice, which may include old ice inclusions
  • Category B ship: A ship not included in category A, designed for operation in polar waters in at least thin first-year ice, which may include old ice inclusions.
  • Category C ship: A ship designed to operate in open water or in ice conditions less severe than those included in categories A and B.

Some Ice Definitions

Ice free watersSea Ice pattern

This means that no ice is present. If ice of any kind is present this term will not be used.

Open water

A large area of freely navigable water in which sea ice is present in concentrations less than 1/10. No ice of land origin is present.

Ice of land origin

means ice formed on land or in an ice shelf, found floating in water.

Sea ice

Any form of ice found at sea which has originated from the freezing of sea water.

First-year ice

Sea ice of not more than one winter growth developing from young ice. It has  a thickness from 0.3 m to 2.0 m.

Medium first-year ice

First-year ice of 70 cm to 120 cm thickness.

Old ice

Sea ice which has survived at least one summer’s melt; typical thickness up to 3 m or more. It is subdivided into residual first-year ice, second-year ice and multi-year ice.


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