Figure B-4 Torque coefficients derived from the self-propulsion tests in level ice
Although variance in the data is large, it can be said that the frequency of the interactions is smaller with stern b than with stern a. This is because stern b has excellent ice-repelling performance, keeping ice fragments away from the propeller.
Examples of the trajectories of the ships in turning tests appear in Figure B-6. Generally, the tactical diameter in ice is larger than that in open water. The size of the tank is so limited that it is extremely difficult to complete turns in common ice model basins. Therefore, the turning ability was judged by the sideways deviation from the original route within the time taken to travel a certain distance, as shown by the trajectories in Figure B-6. The difference in turning test results for each ship type is indicated in the next section, together with the test results for the new ship type.
To evaluate performance when moving through a ridge, the energy necessary to penetrate into and pass over a ridge was calculated from the resistance tests in a ridge. In Figure B-7 (a), examples of measurement of resistance in ridges are shown. Because the model speeds were kept constant, the energy consumed in passing through a ridge can be obtained simply by integration of the resistance during passing over a ridge, multiplied by the model speed. (Figure B-7(b)). The sudden rise in energy consumed at the center of the figure represents the energy consumed to break into the ridge.