Full-Scale Research on the Hull Form Improvement by Bulge

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Fishing boats suffer from much capsizing as compared with other vessels. It may be pointed out that the stability of fishing boats tend to be poor as the bases of the severe operations and the poor management of loading condition as well as the problem with the restrictions of principal dimensions of ship. According to the recent capsizing of the trawler "Ryuho-maru V", Ministry of Land, Infrastructure and Transport of Japan forced to check the stability of existing fishing boats and to improve the stability if not enongh. As for the improvement of the stability, the fitting of a bulge on sidewall of the vessel is one of the best solutions. However, the bulge generally makes a significant increase of hull resistance and loss of speed. In this research, we have investigated into the effect of the bulge on the ship's performances not only on the stability, based on the model experiments and the full-scale experiments of original and enlarged fisheries research ship "Ushio-maru". The principal results are summarized as the followings.(1) The mechanism of the hull resistance by a bulge has been clarified based on the view point of flow field around hull, and the suitable method to design the bulge form has been proposed using Rankine's source method. This technique has been applied to the actual elongation design of "Ushio-maru", and it has been confirmed by the experimental model tests as well as the full-scale trials.(2) The manoeuvring and sea-keeping performance of the bulge-fitted hull form has been also investigated based on theoretical and experimental tests. As the results, the well-designed bulge does not affect on these performances.