Level Ice Clearing in Model and Full Scale Using Azimuthing Propulsion

Abstract

Marine vessels and offshore structures functioning in Earth's frigid zones require ice management to continue their routine operations. Icebreakers are the most influential vessel in assisting marine operations in Polar Regions. The present study is set to analyze the clearance area of level ice using Azimuthing propeller jet in bollard condition, by means of full-scale and model scale experiments. Moreover channel widening and heeling test is performed to analyze the escorting ability of an icebreaker with only using propeller jets. Scope of the current investigation can be incorporated in designing new icebreakers and maintaining desired channel width based on propeller jets effect. Propeller jets can be used to break level ice, when the ship is stationary or moving, where the amount and capacity of breaking or clearing the ice are based on the thrust of the propeller, angle between the propeller jet axis and free surface, and thickness of the ice as well as propeller running time. This paper presents a comparison between full-scale experiments data (carry out in the Gulf of Bothnia, March 2017) and model scale trials performed in Aker Arctic testing facility on the level ice sheet. These experiments were based on image data from external camera and propeller flow parameters, where the area, as well as coordinate calculation, were within 3% of the accuracy from the acquired images. Full-scale ice thicknesses utilized in the experiments were selected and confirmed from surveillance videos. Model-scale images were corrected using Hugin software while ImageJ was used to calculate ice clearance parameters. Propeller thrust and area analysis show 10-22 % of the variation in the results of the model and full-scale experiments for 16 mm thick model ice. 16 mm thick model ice results are much closer to full-scale trials than 25 mm thick model ice. Test results at 30° and 90° pod angles could be extrapolated to design a prototype vessel. Channel widening shows worthy outcome, with the use of Azipods at a speed of 8 kn channel width of 36 m can be attain by positioning the stern Azipods at 30° puller configuration. Changing the pod inclination by 30% will increase the channel width to 20%. In the widening of new level ice channel, 30° pod angle is the most suitable.