Summary of Working Paper No. 66-1996

I.1.10: Ice Environment and Ship Hull Loading along the NSR

By Mikko Lensu, Stephanie Heale, Kaj Riska and Pentti Kujala Helsinki University of Technology, Finland

The Northern Sea Route (NSR) can seldom be transited without encountering ice. This introduces two kinds of uncertainties to navigation: the transit times cannot be exactly defined and a ship runs a certain risk of ice damage. The objective of the project has been to combine ice conditions to transit and damage calculations. The ice conditions are described in terms of distributions for the relevant ice features: ice thickness distribution, floe size distribution, ridge size and spacing distribution, and distributions for lead width and orientation. Based on these it is possible to make calculations for the probabilities of transit times and damages for a certain composition of the ice cover and for a certain set of ship parameters. These distributions can be used as a basis of risk and cost analyses. As a default SA-15 ships strengthened to ULA class have been used. For ice conditions the NSR has been subdivided into seven sea areas and relevant data have been gathered from public sources. The monthly expected ice conditions, transit times and damage probabilities for each sea area are presented. Transit time attains a minimum in October and from January to July a SA-15 ship cannot proceed through at least one of the sea areas without assistance. For a SA-15 ULA class ship the damage probabilities are up to four magnitudes less than if SA-15 was assumed to be of UL class and from August to December the damage probability for the ULA class is virtually zero.

The weakest link of the approach is that the ice conditions are not know in such detail that is required for the transit and damage models. Several simplifications of the theory have been necessary and the better known thickness statistics of the Baltic Sea has been scaled up to obtain an estimate of ice thickness variation along the NSR. As the vast Russian data resources are opening the situation will meliorate in the near future. However, this data is bound to be of the conventional type, following the WMO and Russian traditions, and the need to revise the ice codes to meet the already available theoretical tools is strongly felt.