浅水域の船首沈下(bow squat)の簡易推定

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When a ship is proceeding into the shallow water, ship’s sinkage and bow trim are increased. These tendencies become larger as the bottom clearance is decreased. This phenomenon is generally called as squat, and this sometimes makes the bottom touch or aground in harbour or fairway, and then caused the serious marine disaster such as oil prolusions. The researches of squat have been developed particularly in western countries where many canal and river water ways are provided. There are many methods for predicting the squat. However, the prediction methods that are mainly proposed based on potential theory are complicated and not sufficient in accuracy. In this paper, the simple prediction formula of bow squat is presented based on experimental model tests as well as theoretical approach. Firstly, the increment of sinkage and trim in shallow water is investigated, where it is found that that the Tuck’s simple sinkage model (2) is available for predicting the increment of midship sinkage in stead of the absolute value of sinkage. Meanwhile, the increment of bow trim in shallow water has been introduced from the experimental model tests because of the difficulty of theoretical approach. Finally, adding the bow sinkage in deep water, the simple prediction model of bow squat is proposed here. As the bow squat can be easily calculated from ship’s particulars LPP, B, d, Cb, ship’s speed U, water depth h and width, this formula will help for the evaluation of safety keel clearance on board.
2009-09-25

浅水域の船首沈下(bow squat)の簡易推定

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