Modeling of ship resistance in compressive ice

Dynamic ice fields are one of the greatest hazards for maritime traffic in winter conditions. Converging ice cover, driven by the wind and current stresses, is able to trap even the most powerful vessels, yet little is known about the effects and forces involved. This thesis seeks to derive a simplified method evaluating the added resistance due to compression in the level ice field. In order to model the additional resistance, different topics such as ice conditions and speeds in the Baltic Sea, ice breaking pattern around the vessel and pressures generated in ship-ice interaction, are studied in depth. Natural sea ice is highly heterogeneous and causes high scatter in any measurement values. This study seeks to find the average added resistance in the compressive ice field by defining the average values for ice properties. Method presented is limited to vessels with long, vertical parallel mid ship section such as tankers and bulkers. Results of the calculation model are compared with two different datasets. First consisting of AIS (Automatic Identification System) data analysis of reported compressive situations from winters 2009/2010 and 2010/2011. Second data set is obtained from model ice tests. Correlation with both data sets is visible. Results demonstrate that additional resistance tends to decrease at higher vessel speeds, while level ice resistance increases. In moderate ice going speeds, converging ice field can more than double the total resistance of the vessel