As for the energy to pass through a ridge, the bow Dr was in the same level with the bow A.
Fig. B-14 shows the horsepower calculated from the model test results in calm water. Horsepower of the reamer-mounted Dr-d was higher than in any of the other three designs. The form factor derived from the calm-water resistance tests was highest for Dr-d, and the high form factor resulted in high horsepower. This high form factor was partly caused by the unfavorable distribution of displacement of the aft body. Although this could not be confirmed directly, the separation of flow at the reamers might lead to a somewhat higher form factor. By effectively modifying the reamer shape, with careful consideration of viscous flow field around the aft body, the Dr design with reamers can be expected to yield a notable improvement in its horsepower.
1.5 Evaluation of Hull Forms
Once all of the above results were in, each hull form was evaluated. Preferably, this evaluation would have been conducted using operation simulations as shown in Section 4.4. Unfortunately, detailed environmental data, particularly data about ice conditions in the NSR, were not yet ready at the time this research was conducted. Simulation tests were therefore not possible, and the evaluation of the hull forms was made only qualitatively. The hull forms were evaluated according to five criteria: propulsion performance in level ice, turning ability in level ice, passing capability in a ridge, propulsion performance in calm water and seakeeping performance in waves. Evaluation was conducted by placing each hull form in one of five ranks using the test data to derive a score. Each criterion was weighted according to order of precedence, and the hull forms were finally evaluated by the total score. The weighting factor was determined by the important elements of the NSR navigation from Europe to Japan, such as the proportion of ice navigation (from the Kara Strait to the Bering Strait) to navigation in open water (from the Kara Strait to Europe and from the Bering Strait to Japan), the priorities of the performance elements in ice, etc. Nine combinations of hull forms (A-a, A-b, B-a, C-a, A-d, B-d, D-a, D-d and Dr-d) were evaluated, and the hull forms lacking in the model test data in this project were evaluated according to the data for the similar hull forms available in other sources.
The results of the evaluation are given in Table B-5. Under this way of evaluation, the hull form with the highest total evaluation points is Dr-d, reflecting Dr-d's superior total performance in ice. It will be said that the relatively poor performance in open water was compensated by its excellent performance in ice, although this result partially reflects the greater weighting conferred on ice performance in this evaluation.