This paper presents the key results of a comprehensive study into the nature and magnitude of the mechanisms which contribute to the loads on both open and ducted propellers in the presence of ice. Both model test and full scale trials measurements and visual observations were employed. The nature of the principal components of ice loading are identified and their parametric dependencies are presented. Differences between the interaction of open and ducted propellers with ice are explained and the load limiting effect claimed for the ducted propeller is addressed. The model test results are correlated with equivalent full scale events with remarkably good agreement. The study represents a major advance towards the prediction of design loads for Arctic marine propulsion systems.
When a vessel operates in an ice regime, especially in thick ice broken ice travels along the hull underneath the vessel and is subsequently milled by the propeller. This results in significantly higher forces and moments than are generated in an open water environment and the propeller and propulsion train must be designed for these conditions. The traditional approach to design of ice class propellers and propulsion systems has been to increase the open water design loads using an ice torque factor (Browne and Van der Pas, 1989). This is a function of the ice class of the vessel, which is synonymous with the severity of ice conditions expected in service. The ice torque factor is determined from measurements of shaft loading and propulsion system service experience from earlier vessels. However, it suffers similarly to other purely empirical approaches in that it is no better than the limited data on which it is based and cannot be extrapolated with confidence to cover new propulsion systems and significantly different operating conditions.