Each hull form was numerically ranked in performance from 1 to 5 for each evaluation item. The items are weighted with coefficients that reflect the estimated basis of the number of NSR running days in ice-covered water (from the Bering Sea to Kara Strait) and the number of days in open water (from a port in Japan to the Bering Sea and from the Kara Strait to a port in Europe), as well as the priority of each type of performance in operations in ice-covered waters. The highest total score determined the optimum hull form. Nine 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 others that could not be evaluated directly from the test data were estimated by the available data of similar hull forms.
The results of the evaluation are given in Table 4.1-7. Under this evaluation, the hull form with the highest total evaluation points is Dr-d, reflecting its superior navigational performance in ice. The relatively poor open water performance of the hull form Dr-d was compensated by its excellent performance in ice. It should be noted that this result partially reflects the greater weighting conferred on ice performance in this evaluation. In contrast, for instance, the hull form C-a did well in the open-water evaluation, but its poor performance in ice led to a low total evaluation score.
Based on the above evaluation results, attention was focused on Dr-d as the most appropriate hull form for an icebreaking freighter for the expected requirements of NSR coastal navigation; its performance in ice and open water are summarized in Figure 4.1-21. Given normal rating of 85% of the maximum output of 24,000HP and sea margin of 15%, it is estimated that this vessel will reach speeds of 18.1 knots in open water. In level ice, similarly at 85% of maximum output, the Dr-d ship type is estimated to be capable of continuous icebreaking of ice with 1.2m thickness at a speed of 3.3 knots.