ABSTRACT
Consequently, it is of utmost importance for the vessels operating in the conditions defined above, that they can withstand the load resulting from the ice-structure interaction. The latter may however be in conflict with the economical feasibility of the structural design. Previous studies have indicated that a significant increase in structural weight can
1 INTRODUCTION
The growing interest in arctic sea-based transportation has increased in recent years due to the vast amount of expected natural resources to be found therein. In the context of sea-based transportation the arctic environment may be defined as a sea area with cold climate and at least partial ice-coverage for a period of time. Thus, areas within the arctic circle may be considered as such, but as a sole criterion this does not suffice since areas within the Barents Sea are ice free on a year round basis while the Baltic or the Caspian Sea is ice covered during the winter period. Besides the general presence of ice, which increases the resistance of the vessel and induces local loads to the structure, the cold climate represents another challenge for the vessel’s structure and systems. In other words, the knowledge of current and future ice and metocean condition at the site in question is limited. Prediction models are associated with high uncertainties and
occur as a result of higher ice classes. In a study of the structural integrity of cargo containment systems in LNG carriers (Kwon et al., 2008), an increase of about 4-6% was found when changing scantling compliance from Baltic Class Ice 1A to IACS Polar Class 7. This is a significant increase in weight, especially since the classes are considered to have equal performance. An increase of this degree will for a merchant vessel result in a proportional reduction in payload capacity. This poses a challenge in a conceptual engineering phase, as equivalency between classifications does not necessarily translate to similar structural mass and therefore cost. In an attempt to find an approach to this complex problem, a method was suggested in a report for the Krylov Shipbuilding Research Institute (Appolonov et al. 2007). It suggests a system of determining classification equivalency, by comparing class requirements for frame cross sectional area, with one spacing plate flange width, in the ice belt. In the report it is noted, that the problem of estimating ice strengthening structure weight is especially important for ships of new types that do not have close analogies, such as large Arctic tankers and LNG carrier. Another approach comparing class equivalency was performed by the Helsinki University of technology and Lloyd’s Register (Bridges et al, 2005) by comparing the principal scantlings between the Russian Register Rules and the IACS unified requirements, for a selected case study in the Russian Varandey region. Similar to the Appolonov et al. (2007) only the ice-strengthened regions are considered and thereby the influence on the possible changes in local and global scantlings outside these regions have been neglected.
