Author(s): Pekka Kannari
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Keywords: No Keywords
Abstract: During winter 1986 full-scale tests with the Baltic icebreaker KARHU were conducted by the Wartsila Arctic Research Centre. The ice conditions in the Gulf of Bothnia included level ice up to 85 cm and pressure ridges up to 20 metres thick. The icebreaker KARHU is a 7500 hp, four-screw icebreaker, capable of breaking ice of about 90 cm in continuous mode. The vessel was fitted with a nozzle propeller on the port side stern shaft, while the starboard screw was left unducted. This unique testing set-up allowed simultaneous comparisons between an open propeller and a nozzle propeller in exactly the same ice conditions. In addition to the normal shaft measurements, one blade of each stern propeller and the supports of the nozzle were instrumented with strain gauges. The hydrodynamic forces and moments, and the ice loads acting on the propulsion system could be measured. This type of instrumentation on a full-scale icebreaker has not been reported before. An underwater video monitoring system was fitted on both sides, which permitted visual observation of the behaviour of ice blocks at the propellers. The open propeller and the nozzle propeller could be observed simultaneously. Model tests were conducted at the Wartsila Arctic Research Centre with the same set-up as in the full-scale tests. The blades of the model propellers were instrumented and the behaviour of the propulsion motors was simulated. Both the visual and measured data were compared with the full-scale results and the correlation was very good. The paper describes the testing set-up, the instrumentation and the tests in both full and model scale. Some examples of the results are presented and a comparison with the model tests is made.
Year: 1988