バルクキヤリヤーの脚荷吃水設定法

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In the previous papers, the authors made some statistical investigations of bow bottom emergence of a ballasted bulk carrier in rough seas. Here, they present the results of a study on determination of fore and after draughts of ballasted bulkcarriers in rough seas with consideration of the criteria of slamming and propeller racing. The authors carried out the theoretical calculations of response operators of relative bow motion and relative stern motion of a bulk carrier selected as a typical ship form, in regular head waves under nine different ballasted conditions which were determined by combining three different fore draughts and three different after draughts. Then, they estimated theoretically the probabilities of occurrence of slam and propeller emergence among rough seas corresponding to the average sea states of the North Atlantic under various wind velocities, by using the derived response operators and the wave spectra which were assumed so as to represent the sea states realistically. And finally they made the estimation of the critical fore draught with respect to slamming and the critical after draught with respect to propeller racing. These theoretical estimations were made for geometrically similar ships having different lengths. The critical fore draught and the critical after draught are given in charts as functions of ship length with parameters of sea state and ship speed. By investigating those results, the following facts were found: (a) When the fore draught being constant, the larger after draught causes little increase of relative bow motion and probability of occurrence of bow emergence or slam. Therefore, the frequencies of bow emergence and slam are almost dependent on the fore draught only. (b) When the after draught being constant, the larger fore draught causes a little increase of relative stern motion and probability of occurrence of propeller emergence. Therefore, the propeller emergence is almost dependent on the after draught only. (c) The probabilities of occurrence of slamming and propeller racing decrease considerablly with increase of ship length. (d) The probability of occurrence of slamming decreases considerablly with decrease of ship speed, whereas the probability of occurrence of propeller racing does not, but somewhat increases with that. Probabilities of occurrence of slamming and propeller racing calculated by the theoretical method are largely dependent on the values of threshold velocity and critical propeller emergence respectively. Therefore, the reliabilities of calculated probabilities are almost dependent on the reliabilities of the values of those. It is necessary to make further studies on threshold velocity and critical propeller emrgence. However, the results obtained here would be available for the purpose of determination of fore and after draughts of ballasted bulk carriers in rough seas at the view point of comparative design for ships of different lengths.
社団法人日本船舶海洋工学会の論文
1967-02-28

バルクキヤリヤーの脚荷吃水設定法

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