This bow form has a stem angle close to 25 degrees (same as bow A) and smaller entrance angle of waterline than bow A; a small fore/buttock line angle near the fore shoulder; knuckle near station 8-1/2; and reamer along the knuckle line. The reamer bulges as much as 5% of the ship's half-width. The reamer and shorter parallel fore part are installed to provide better turning capability in ice. To verify the effect of the reamer, the reamer was built as a separate, removable part in the model; when the reamer is fitted the bow is called Dr, and when the reamer was removed it is called simply D. A new stern "d" was designed to improve turning performance. This stern d has a shorter parallel part and its frame lines between S.S.1/2 and S.S.3 form moderate angles with the load waterline. Moreover, the knuckle in stern b was moderated in stern d to get better propulsive performance.
Four kinds of model tests were conducted on ship forms D-d and Dr-d: Resistance test, self-propulsion test and turning test in level ice, and resistance test in an ice ridge. In addition to these, resistance and self-propulsion tests were carried out in calm water. As an example, we show here the results of the turning test in level ice (Figure 4.1-20). This illustration compares the results for the new ship forms with those of bows A and B. As the diagram shows, Dr-d, the ship design incorporating the reamer, demonstrates the best turning performance. A comparison between models A-a and A-d clearly shows the effect of the stern form on turning performance. Along with the pronounced effects of the reamer, the short parallel part of the stern d, whose frame lines formed moderate angles with the load waterline, significantly improves the turning performance. Note that the turning performance of previous bows A and C (not shown) are roughly equivalent, while that of B is poorer.
Figure 4.1-20 Results of the turning test in level ice
Based on the summarized results of the model tests, each hull form was evaluated. Ideally, the evaluation should have been conducted through a sophisticated numerical simulation as described in Section 4.4, fully utilizing the various performance data for each hull form. Unfortunately, simulations could not be used because the requisite environmental data, particularly the detailed information on ice conditions, were not ready at the time that this research was conducted. Instead, a qualitative evaluation was made for each hull form based on model test results, taking account of the relative importance of each aspect of performance in ice and open water.
The evaluation of the hull form was made for five items based on the test results: propulsion performance in level ice, manoeuvrabilty in level ice, ridge-passing capability, power requirement in calm water and seakeeping qualities.
