6. A Consideration on the Mechanism of Occurrence of Broaching-to Phenomena

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When a ship is traveling in the following seas, of which the wave length is almost twice the ship's length, at an advance speed nearly equal to the wave celerity, the ship is violently turned against the hard-over helm. This phenomenon is called the broaching-to, and has been feared by the seamen. Several different causes are now advocated with regard to the occurrence of the broaching-to ; a) decrease in rudder force in the following seas, b) loss of directional stability when a ship travels on the down slope of a wave, and c) generation of turning moment due to the cross flow component of the orbital motion of wave particles. In this paper, the authors discuss the propriety of the traditional notions stated just above by examining them with the hydrodynamic data obtained through the captive model tests. As a result of the examination, the authors conclude that any of the above stated causes is not the primary cause of the occurrence of the broaching-to phenomenon. In order to understand the characteristics of the lateral motion of a ship traveling in the following seas, simulation studies of surge, sway and yaw motions were performed. As the result, it is found that the violent turn of a ship traveling on the down slope of the following wave is excited by the wave exciting yaw moment when the ship has an advance speed equal to or slightly lower than the wave celerity, and moreover the encounter angle of the ship to the wave is approximately equal to 20 or 30 degrees. Consequently, the authors conceive that the broaching-to phenomenon occurs when the wave exciting yaw moment becomes remarkably high compared with the hydrodynamic moment induced by the hard-over helm. This notion is verified by analysis of broaching-to phenomena observed at full-scale experiments in the sea.
社団法人日本船舶海洋工学会の論文

6. A Consideration on the Mechanism of Occurrence of Broaching-to Phenomena

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