Polar Class (PC) refers to the ice class assigned to a ship by a classification society based on the Unified Requirements for Polar Class Ships developed by the International Association of Classification Societies (IACS). Seven Polar Classes are defined in the rules, ranging from PC 1 for year-round operation in all polar waters to PC 7 for summer and autumn operation in thin first-year ice.
The IACS Polar Class rules should not be confused with International Code for Ships Operating in Polar Waters (Polar Code) by the International Maritime Organization (IMO).
The development of the Polar Class rules began in the 1990s with an international effort to harmonize the requirements for marine operations in the polar waters in order to protect life, property and the environment. The guidelines developed by the International Maritime Organization (IMO), which were later incorporated in the Polar Code, made reference to the compliance with Unified Requirements for Polar Ships developed by the International Association of Classification Societies (IACS). In May 1996, an "Ad-Hoc Group to establish Unified Requirements for Polar Ships (AHG/PSR)" was established with one working group concentrating on the structural requirements and another working on machinery-related issues. The first IACS Polar Class rules were published in 20007.
Prior to the development of the unified requirements, each classification society had their own set of ice class rules ranging from Baltic ice classes intended for operation in first-year ice to higher vessel categories, including icebreakers, intended for operations in polar waters. When developing the upper and lower boundaries for the Polar Classes, it was agreed that the highest Polar Class vessels (PC 1) should be capable of operating safely anywhere in the Arctic or the Antarctic waters at any time of the year while the lower boundary was set to existing tonnage operating during the summer season, most of which followed the Baltic ice classes with some upgrades and additions. The lowest Polar Class (PC 7) was thus set to the similar level with the Finnish-Swedish ice class 1A. The definition of operational conditions for each Polar Class was intentionally left vague due to the wide variety of ship operations carried out in polar waters.
Polar Class notations
The IACS has established seven different Polar Class notations, ranging from PC 1 (highest) to PC 7 (lowest), with each level corresponding to operational capability and strength of the vessel. The descriptions given in the rules are intended to guide owners, designers and administrations in selecting the appropriate Polar Class to match the intended voyage or service of the vessel. Ships with sufficient power and strength to undertake "aggressive operations in ice-covered waters", such as escort and ice management operations, can be assigned an additional notation "Icebreaker".
The lowest Polar Classes (PC 6 and PC 7) are roughly equivalent to the two highest Finnish-Swedish ice classes (1A Super and 1A, respectively). However, unlike the Baltic ice classes intended for operation only in first-year sea ice, even the lowest Polar Classes consider the possibility of encountering multi-year ice ("old ice includions").
|Polar Class||Ice description (based on WMO Sea Ice Nomenclature)|
|PC 1||Year-round operation in all polar waters|
|PC 2||Year-round operation in moderate multi-year ice conditions|
|PC 3||Year-round operation in second-year ice which may include multi-year ice inclusions.|
|PC 4||Year-round operation in thick first-year ice which may include old ice inclusions|
|PC 5||Year-round operation in medium first-year ice which may include old ice inclusions|
|PC 6||Summer/autumn operation in medium first-year ice which may include old ice inclusions|
|PC 7||Summer/autumn operation in thin first-year ice which may include old ice inclusions|
In the Polar Class rules, the hull of the vessel is divided longitudinally into four regions: "bow", "bow intermediate", "midbody" and "stern". All longitudinal regions except the bow are further divided vertically into "bottom", "lower" and "icebelt" regions. For each region, a design ice load is calculated based on the dimensions, hull geometry and ice class of the vessel. This ice load is then used to determine the scantlings and steel grades of structural elements such as shell plating and frames in each location. The design scenario used to determine the ice loads is a glancing impact with ice.
In addition to structural details, the Polar Class rules have requirements for machinery systems such as the main propulsion, steering gear, and systems essential for the safety of the crew and survivability of the vessel. For example, propeller-ice interaction should be taken into account in the propeller design, cooling systems and sea water inlets should be designed to work also in ice-covered waters, and the ballast tanks should be provided with effective means of preventing freezing.
It should be noted that while the rules generally require the ships to have suitable hull form and sufficient propulsion power to operate independently and at continuous speed in ice conditions corresponding to their Polar Class, the ice-going capability requirements of the vessel are not clearly defined in terms of speed or ice thickness. In practice, this means that the Polar Class of the vessel does reflect the actual icebreaking capability of the vessel.
Polar Class ships
The IACS Polar Class rules apply for ships contracted for construction on or after 1 July 2007. This means that while vessels built prior to this date may have an equivalent or even higher level of ice strengthening, they are not officially assigned a Polar Class and may not in fact fulfill all the requirements in the unified requirements. In addition, particularly Russian ships and icebreakers are only assigned ice classes according to the requirements of the Russian Maritime Register of Shipping which maintains its own ice class rules parallel to the IACS Polar Class rules.
Although a number of ships have been built to the two lowest Polar Classes which correspond to the two highest Baltic ice classes, there are only a handful of vessels assigned ice class PC 5 or higher. While the 2012-built drillship Stena IceMAX has a hull strengthened according to PC 4 requirements, the vessel is not capable of independent operation in ice and as a whole has ice class PC 6. The South African polar research vessel S. A. Agulhas II, also delivered in 2012, was the first ice-capable vessel built to ice class PC 5. The Canadian-flagged icebreaking bulk carrier Nunavik, operated by Fednav and used to transport copper and nickel from the Nunavik Nickel Project, was built to ice class PC 4 in 2014. The new Finnish icebreaker Polaris was built in 2016 to the same ice class with additional notation "Icebreaker(+)" where the last notation refers to additional structural strengthening based on analysis of the vessel's operational profile potential ice loading scenarios. The Netherlands-based ZPMC-Red Box Energy Services operates two PC 3 class deck cargo ships, Audax and Pugnax, which were built in 2016. In addition, China and Norway are currently building an icebreaking polar research vessel to the same ice class.
As of 2017[update], there are no ships in operation or under construction to ice classes higher than PC 3. The proposed Canadian polar icebreaker, CCGS John G. Diefenbaker, is designed to ice class PC 2 Icebreaker(+).
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