The reamer bulged to as much as 2.5% of the width of the ship.To verify the effect of the reamers on turning ability, the reamer was built as a separate, removable part of the model. When reamers were fitted, the bow was called Dr, and without the reamers it was called D. To boost the turning ability, inclined frame lines around the load waterline were adopted between S.S. 1/2 and 3 and a short parallel body was also adopted. Also, based on the stern b, which had an excellent capability of repelling ice from the propeller disk, in the newly designed stern d, the propulsion performance was improved by adopting inclined knuckle lines.
Four kinds of test in ice model basins were carried out on the new ship types Dr-d and D-d: resistance and self-propulsion tests in level ice, turning test in level ice and resistance test in a ridge. Resistance and self-propulsion tests in calm water were also conducted. All of these tests were entrusted to NKK and MHI.
The results of the resistance tests in level ice appear in Figure B-12. The resistance in bow D fell between those of bow A and B. Interestingly, the ship with a reamer, Dr, showed no significant difference with D in terms of ice resistance. This is probably because the width of the reamers was restricted to only 2.5% of the ship width, width of the parallel part of the ship. Local width of the ship at the reamer was not wider than the channel width formed by the icebreaking process, as the channel is slightly wider than the ship width. The reamers' contribution to the resistance could therefore be low. Note that ship width B used in the non-dimensional coefficient of resistance does not include the reamers.
The turning test results of the newly designed ship in level ice, together with those of bows A and B, are shown in Fig. B-13. As the figure shows, model Dr-d, the new model with reamers, exhibits the best turning ability. The turning ability of bows A and C (not shown) were roughly equal, with the poorest ability turned in by bow B.
