Changing the bow and propeller type had no major effect on turning ability. The ratios of turning circle to ship length and of advanced distance to ship length were about 3:0, respectively.
The thrust increase coefficients, obtained from the seakeeping tests in waves, are shown in Figure B-10. The thrust increase coefficient was highest for bow B, particularly in the short wave range. This is because bow B has a relatively blunt entrance angle around the load waterline. In contrast, bow C had the lowest value for the coefficient, and therefore for resistance increase in waves, because of its small entrance angle around the load waterline.
1.4 Development of a New Ship Type and the Model Tests
The test results of various combinations of bows A, B and C and sterns a and b can be summarized as follows.
* Bow B had the best performance in terms of ice resistance.
* Turning performance in ice was poor in all cases. That of bow B was particularly poor.
* Although stern b was the better of the two in terms of capability of repelling ice from the propeller disk, stern a offered the better propulsion performance.
* Although little difference between bow types was found in terms of propulsion performance in calm water, bow A was the best, followed by B and then C.
* Thrust increase in waves was lowest for bow C, followed by A and then B.
Taking all of these results into account, new forms of bow and stern were designed and tested.
The body plan of the newly designed ship is illustrated in Figure B-11. A new bow type was developed that incorporates the low-resistance performance of bow B and the calm-water performance of bow A. This bow has a stem angle of 25°(same as that of bow A) but a larger entrance angle of load waterline than bow A, to ensure excellent icebreaking capability of the stem part. To improve turning ability in ice, inclined frame lines and knuckles at the sides around the load waterline were adopted between S.S.81/2 and 9, and reamers were added along the knuckle lines as well.
