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Summary of Working Paper No. 110-1998

I.1.8 Influence of Ice Compression on Feasible Navigation on the Northern Sea Route. Part II.

By K. Juurmaa, T. Heideman, and A. Uuskallio, Kvaerner Masa-Yards Arctic Research Centre, Helsinki, Finland; M. Patey and L. Kosomaa, Helsinki University of Technology, Espoo, Finland

Part II of the INSROP Project I.1.8 was initiated to find better ways than the subjective ball scale to describe the ice compression and its influence on the ice resistance. The selected way to proceed was to analyse existing full scale measurements and to try to repeat the corresponding measurements in model scale under controlled conditions. The only full scale results found were those of the Russian icebreaker Lenin. Based on these the resistance increase under different severity of ice compression was determined.

The model tests were performed in the ice laboratory of the Helsinki University of Technology. Two models were used for the testing. One was a model of an icebreaker similar to the full scale reference vessel icebreaker Lenin and the other was a model of an arctic cargo vessel. The model test results with the ice breaker model showed that a useful measure to describe the ice compression is Compaction Factor. This is the ratio between the areas of an uncompressed ice field and the area of a compressed ice field. It is assumed that the forces within the ice field are transferred through compaction. This is a fact at least in larger scale and in ice fields that are broken due to compression. Based on the comparison between full and model scale results, it seems that Compaction Factors in the range of 1.20 - 1.53 are comparable to ice compression of 2 balls on the 0 - 3 balls scale.

The results with the model of the arctic cargo vessel proved to be somewhat doubtful. Based on these results the Compaction Factor has lower influence on the resistance increase with the cargo vessel than with the icebreaker. The tests were performed with a segmented model and that offers an opportunity for further analysis of the forces acting on the vessel. It is recommended that this analysis and possible further testing will be performed at a later stage.