Propulsion shaft line ice-induced dynamic torque response calculation and comparison to full scale

Winter and arctic conditions set specific requirements for ship design in the form of icecovered water. One major aspect is propeller and propulsion design for ice conditions. The propeller-ice interaction has been widely studied over the years and there are current regulations among classification societies to ensure safety of ice-going vessel propulsion design. The design process involves propeller dimensioning for ice loads as well as rest of the propulsion line. The propeller-ice interaction causes torque loading to the propulsion system. This is dynamic in nature and is somehow to be dealt with in design phase. In this paper, the principle of dynamic propulsion shaft line model is presented, the model is validated with ship design torsional vibration analysis calculations and the time domain response calculation is performed with ice class requirements, and these results are compared with full scale measurements. In full scale tests, the propulsion shaft line input torque from propulsion motor was measured simultaneously with rotating speed. By comparing the measured and simulated dynamic response, it is possible to backward determine the magnitude of ice torque excitation. In conclusion, the propulsion shaft line dynamic ice-induced torque response in the measurements was significant, even so that the ice class required excitation level for simulation was underestimating the torque response level encountered in measurements.