Ice class

Ice class refers to a notation assigned by a classification society or a national authority to denote the additional level of strengthening as well as other arrangements that enable a ship to navigate through sea ice. Some ice classes also have requirements for the ice-going performance of the vessel.

The first requirements for merchant ships to be escorted by icebreakers were set in Finland in 1890, after winter traffic to the port of Hanko was started. In the past, different classification organizations had different standards, rules, and ice classes. Converting between the Baltic and Arctic systems is not usually done. Recently, the two different class systems have been defined by the International Association of Classification Societies (IACS) and the International Maritime Organization (IMO).

Not all ships are built to an ice class. Building a ship to an ice class means that the hull must be thicker, and more scantlings (aggregate of girders, beams, and bulkheads resulting in stronger structural integrity) must be in place. Sea chests (openings in the hull for seawater intake) may need to be arranged differently depending on the class. Sea bays may also be required to ensure that the sea chest does not become blocked with ice. Most of the stronger classes require several forms of rudder and propeller protection. Two rudder pintles are usually required, and strengthened propeller tips are often required in the stronger ice classes. More watertight bulkheads, in addition to those required by a ship's normal class, are usually required. In addition, heating arrangements for fuel tanks, ballast tanks, and other tanks vital to the ship's operation may also be required depending on the class.

Product tanker Ternvik escorted to the port of Oulu by the Finnish icebreaker Sisu]] In the Finnish-Swedish ice class rules, merchant ships operating in first-year ice in the Baltic Sea are divided into six ice classes based on requirements for hull structural design, engine output and performance in ice according to the regulations issued by the Swedish Maritime Administration and the Finnish Transport Safety Agency (TraFi). International classification societies have incorporated the Finnish-Swedish ice class rules to their own rulebooks and offer equivalent ice class notations that are recognized by the Finnish and Swedish authorities.

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