Full-scale ice impact to an azimuthing thruster in laboratory conditions

Ships navigating in winter conditions frequently come in contact with ice blocks floating on the waterways. The ice blocks can collide with the propulsion machinery of the ship. Especially the interaction between ice and ship azimuthing propulsion call for greater understanding. Ice blocks can collide with the azimuthing propulsion units in many different ways, one of them being the propulsion unit hitting the ice block as the ship advances. This is an impact type loading case and the dynamics of the thruster and ship hull affect to the load response level obtained in this case. In a dynamic system, the damping is greatly affecting to the response level. To study the dynamics and damping in an ice impact event, a full-scale test opportunity was found in an azimuthing thruster test bench. An impact test with a full-scale thruster and ice blocks was carried out in the laboratory with velocities corresponding to realistic ship operating speeds. In addition, numerical analyses of the ice-structure interaction were carried out and structural response was compared with the impact test measurements. Comparison between the simulations and the tests gave valuable information about the thruster dynamics during the ice impact.