Ice tank tests of a highly skewed propeller and a conventional ice-class propeller in four quadrants

Recent work to update regulations for ice-class ships has resulted in, amongst other things, new methods for dimensioning ice-class propellers. These methods have focussed on the more traditional propeller geometry and arrangements so that unconventional designs, such as highly skewed propeller blades and azimuthing propellers, have been excluded and must be treated as special cases. Also, elements of the design methods are based on limited empirical sources and as such need testing, verification, and perhaps modification. -- To address some of these issues, an experimental investigation was undertaken in the ice tank at the Institute for Marine Dynamics (IMD) using two different propeller models. A model of the propeller on the passenger ferry MV Caribou was tested specifically to investigate a highly skewed propeller under ice loading over a range of operating and ice conditions. The second propeller tested was a more conventional ice-class propeller from the R-Class icebreaker. The R-Class propeller model was tested over a wide range of operating conditions to give loading characteristics in all four quadrants. Such extreme loading might be experienced by fixed and controllable pitch propellers in off-design conditions, and by azimuthing propellers. The set of experiments involving the R-Class propeller were done over a range of ice strength conditions to examine nominal ice strength variation effects on the propeller loads. Based on the experimental results it is concluded that a highly skewed propeller behaves in a similar manner to that of a conventional ice-class propeller. In addition, the tests conducted in all four quadrants of propeller operation concluded propellers do not experience the greatest loads in quadrant 1, which is currently used as the design criterion. Rather, the largest loads are experienced in quadrants 2 and 3 and modifications to current design proposals should consider this detail.