出版社：The Japan Society of Naval Architects and Ocean Engineers
摘要：When a ship is travelling in a following sea, of which the wave length is almost twice the ship's length, with an advance speed nearly equal to the wave celerity, the ship is violently turned against the helm of rudder. This phenomenon is called the broaching-to, and feared by the seamen for a long time. There exist some different notions as regards the immediate cause of occurrence of this phenomenon. The widely supported notions are as follows a) reduction of rudder effectiveness in the following seas, b) instability of course keeping of a ship travelling on the downhill slope of wave, and c) the action of turning moment due to the cross flow component of the orbital motion of water particle.In this paper, the authors discuss the propriety of the traditional notions stated just above by examining them with the hydrodynamic data obtained from the restrained model tests. As a result of the examination, the authors conclude that any of the above stated causes is. not the immediate cause of occurrence of the broaching-to phenomenon.In order to understand the characteristics of the ship motion travelling in a following sea, a simulation study of surge, sway and yaw motions is executed. As the result, it is found that the violent turn of a ship travelling on the downhill slope of the following wave is excited by the wave turning 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 around 20 and 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 of course keeping generated by the helm of rudder. This notion is verified by analysis of the broaching-to phenomenon observed at a full-scale experiment in the sea.
