Ice Impact Loads on Blades of Cycloidal Propellers

Cycloidal propellers, also known as vertical axis propellers, have so far seen limited use in ice-covered waters. However, as these kind of propulsors are becoming more common with new manufactures emerging, the ice loads on propeller blades also becomes an important topic. It should be noted that currently there are no public methods or classification rules for calculating ice loads on cycloidal propellers. The paper focuses on the Baltic Sea ice conditions, and the Finnish-Swedish ice class rules are used as a basis for the studied cases. For merchant ships travelling in the Baltic Sea, the most frequent ice impact scenario is the case where the ship is travelling in a brash ice channel. In comparison to the traditional screw propeller, there are some distinct differences when considering cycloidal propeller. Due to lower hydrodynamic loading of the blades, the rotational speed of cycloidal propeller is lower. Also, the axis of rotation is vertical, and the blades are usually longer than in a comparable screw propeller. When considering the impact load scenario, it is probable that it is quite different from the milling-type ice load scenario, which is basis for the ice load calculation of screw propellers. In the milling-type load scenario, ice is not only crushed, but partly also cracked and spalled. However, in cycloidal propeller case, the blade shape is blunter, and the impact is expected to be more crushing type. VTT ice impact load model, which solves the impact in time domain, is used to analyse a realistic propeller case to give better understanding on the ice load magnitudes for the blade. Results are compared to a similar size screw propeller. Lastly, limitations and further work are described. For example, the hydrodynamic non-contact loads during the ice interaction, can be estimated in future studies with the help of CFD.