The first edition of the Polar Class (PC) Rules, based on the IACS Unified Requirements for Polar Ships, was published in the January 2008 edition of the Ship Rules. The Polar Class notations cover design requirements for hull structure and machinery systems, and are intended for vessels operating Arctic or sub-Arctic waters during independent operation or with assistance from icebreakers.

The Polar Class Rules will replace the existing DNV Arctic Rules which have set standard for design of high ice class vessels to be operated in the Arctic since the mid 1980s, but the traditional DNV Arctic Rules will in a transition period still remain as an alternative to the new Polar Class notations. Even though the Polar Class notations requirements are released, a significant effort is currently put into further development of the Rules and to fill in the gaps which are present in the current Rules. As a consequence of this, the Rules are given as tentative, allowing application of the most recent knowledge gained during this ongoing revision process.

Morten Mejlænder-Larsen, Programme Director for Arctic shipping activities in DNV, says that the implementation of the final Unified Requirements for Polar Ships represents a big step ahead in the harmonization of rules for ice-strengthened vessels designed for Arctic operations.

DNV has actively participated in the development and implementation of the Polar Class requirements since the mid 1990s, which culminated in the 2006 approval by the Council of International Association of Classification Societies (IACS) and subsequently in the outset of the first Rule edition in 2008. At the same time, IACS formed revision groups for both hull and machinery requirements, and DNV is taking an active role in the further development of the Rules.

During the past years, the new Polar Class has received an increased amount of attention from ship owners and yards. Manufactures and designers are now preparing to apply the Polar Class rules, and DNV is putting a lot of effort in assisting customers and clients with the interpretation of the Polar Class requirements and in explaining the basic concepts of. The traditional DNV Arctic notations (POLAR and ICE) are generally well known and commonly accepted with regard to strength, cost and operability. With the introduction of the new Rules, the industry is again searching a more in-depth understanding of the applicability of the different Polar Classes with regard to capability and performance.

The Polar Class is divided into seven classes, ranging from the highest ice class PC1, which is to be linked to a vessel capable of operating safely anywhere in the Polar oceans at any time of year, to the classes PC6 and PC7, which are intended for Summer/Autumn operation in first year ice and which are comparable with the two highest Baltic ice classes.

The hull requirements are based on a rationally linked collision scenario between the vessel and an ice feature, usually referred to as a glancing impact. The loading is then further processed and applied together with predefined response criteria for scantling control. The Rules include specific requirements for local scantling, while design procedures for e.g. primary structure and appendages are in the current edition to be based on the current practice of each individual classification society. It is anticipated that most of the missing items in the current hull requirements will be covered in the next revision.

Contrary to most well-known rules from the past three decades, the Polar Class machinery requirements do define the ice interaction loads on the propellers. Equations to calculate minimum scantlings for propeller and shafting components e.g. propeller blade thicknesses, or shaft diameter are, however, not given in the current revision of the Rules. Consequently, designers, makers and Class Societies are forced to apply advanced analysis in their design and verification processes in order to verify Polar Class compliance against defined loads and permissible stresses for the components. In the new revision of the Rules, which is about to be finalized, many of the gaps which are present in the current revision will be removed.

The chairman of the IACS project team for updating the machinery requirements, Lasse Norhamo, DNV principal engineer, says: “The work on the revision of the machinery requirements has been on industry hearing and is now close to be finalized. In this revision, the detailed requirements for most of the lacking items in the first edition are introduced. It is expected that this will be adopted within this year.”