In the present paper, as the first stage of developing an onboard system for supporting decision making of ship navigators, a practical method to predict height, length and directions of waves in real-time onboard using measured ship motion data is developed. This method is based on the comparison between calculated ship motions by a strip method and measured ship motions of five degrees of freedom except for surging. To confirm the accuracy of this method, experiments using a real ferryboat in a Japanese domestic route are carried out. The results show a fairly good agreement between the obtained wave characteristics by the system and the observed ones by sailors.
In the design of a ship, the sailing performances of the ship in waves are carefully surveyed for wide points of views, for example stability, seakeeping and so on. The results of the surveys are given to the ship as a stability booklet and other detailed documents. Navigator, however, usually operate their ships in rough seas on the basis of own skill obtained in long experience. In the real navigating situation in very severe rough seas, it is sometimes difficult for navigators to use such detailed materials mentioned above for safety navigation. Therefore, it is important and helpful to develop some tools to monitor the ship motions and seas on board automatically and to report dangerous situation to navigator. In this study, the authors develop a practical method to identify the height, frequency and direction of encounter waves from measured data of ship motions and ship speed. This method will be one of key technologies for developing an onboard information system for supporting decision making of officers of a ship in heavy seas.
Many methods to identify encounter waves onboard have been developed by many researchers.
