International Shipbuilding Progress - Volume 13, issue 137

Authors: van Lammeren, W.P.A. | Pangalila, F.V.A.

Article Type: Research Article

Abstract: The propulsive performance, the bending moments amidships and the motions of a ship model representing a 24,000 DWT bulkcarrier were measured in smooth water and in irregular long-crested waves, over a speed range corresponding to 10 knots through 16 knots. The model was tested with a conventional bow and with a 9% bulb added respectively. In the loaded condition and for the speed range considered with smooth watertests, no saving in power was measured for the model with the bulbous bow in comparison with the model with the conventional bow. In ballast, however, smooth water tests showed that …a reduction in power was obtained for speeds above 13 knots when the ship model was fitted with a bulb [3]. The waves in which the models were tested correspond to long-crested irregular head seas, windforce Beaufort 6 with a significant wave height of 2.90 m and an average period of 7.2 seconds. In the ballast condition for the sea described, the model with the bulbous bow still required less power than that with the conventional bow to attain speeds above 13 knots. Only small differences in bending moments due to rough seas were measured between the two models and hardly any difference in pitch angle. Smaller amplitudes of the relative motion of the bow were measured at the model with the bulbous bow when it was in loaded condition. In the ballast condition the average immersion of the propeller was reduced by the bulb. Show more

DOI: 10.3233/ISP-1966-1313701

Citation: International Shipbuilding Progress, vol. 13, no. 137, pp. 3-13, 1966

Authors: English, J.W.

Article Type: Research Article

Abstract: The division of thrust in a lateral thrust unit between the rotor and the ships hull is considered and shown to be of the utmost importance in the design of a thrust unit. The importance of duct inlet roundings is discussed and efficient intake shapes are derived for a unit employing ducting of uniform cross-sectional area and hence having no flow contraction or diffusion. Suggestions based on practical considerations are made for modifying these shapes. These allow for added ship resistance due to the presence of the openings and the use of the unit for slow speed manoeuvring. The question …of closing doors for the unit is also discussed and finally suggestions are made for testing full scale units in certain suitable cases. Show more

DOI: 10.3233/ISP-1966-1313702

Citation: International Shipbuilding Progress, vol. 13, no. 137, pp. 14-28, 1966

Authors: Bluston, H.S.

Article Type: Research Article

Abstract: Methods are given for obtaining the optimum source distribution for a large, linear, sonar array. An ‘optimum’ distribution is defined here as one which minimizes the pattern beam width for a given side lobe level. Numerical results are given for various arrays having between 11 and 201 elements and a - 20 db side lobe level, and it is shown that these results can be used over a wide range of steering angles θ c and element spacings d / λ . It is then shown that there are bounds on …d / λ for a given θ c and tables are given for these bounds. Finally, comparisons are made of the patterns due to an ‘optimum’, ‘modified optimum’ and uniform distribution for a 201 element broadside sonar array. Show more

DOI: 10.3233/ISP-1966-1313703

Citation: International Shipbuilding Progress, vol. 13, no. 137, pp. 29-37, 1966