The ratios of wave length to ship length were varied between 0.75 and 2.00, simulating wave height in the Bering Sea, where average wave height is 4.07m.in winter.
In addition to the above tests, wake measurements and the propeller test in open water were also conducted.
1.3 Test Results
On the basis of the test plans summarized above, each of the three research organizations conducted its own series of tests, using its own tanks. Not surprisingly, the tests provided copious data and prolific results on the performance of ships. Therefore, the following discussion will be restricted to the main results only.
* Test results in ice
The results of measurement of icebreaking resistance in each ship type appear in Figure B-3. Because icebreaking resistance is largely dependent on the shape of the bow, only one stern type, stern a, was combined with all three types of bow. To confirm the effect of the stern, some tests were also conducted with the combination A-b. No significant difference with A-a, however, was found for model A-b. The test results indicate that the ice resistance of bow B is apparently lower than the others. The next best bow type was C, with the worst resistance exhibited by the conventional wedge-type bow A.
An example of the torque coefficient obtained by the self-propulsion tests in level ice appears in Figure B-4. The solid lines in the figure are the results of an overload test conducted in open water. In the self-propulsion tests in level ice, interactions between the propeller and ice fragments generally raise the torque coefficient higher than in the results of the open-water overload test. A similar tendency was also obtained in this case. However, the results of self-propulsion tests with twin-propeller ships in ice were reported in some cases to be as high as twice the results for overload tests in calm water. The difference between twin-propeller and single-propeller models was found not to be significant in torque coefficient between the overload and the self-propulsion tests. One of the reasons is that the single-propeller markedly reduces interactions between the ice and the propeller in comparison with the twin-propeller. The frequency of the ice-propeller interactions during a ship-length run as a function of the Froude number is plotted in Figure B-5.
