Abstract
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.As the first stage of developing such a onboard navigating assistant system for supporting decision making of navigators, the authors proposed a simple and practical method to identify height, frequency and direction of encounter waves. This method is based on the comparison between response function database and measured ship motions. To confirm the accuracy of this method, experiments using a ferry model in tank and a real passenger/vehicle ferry operated in a Japanese domestic route are carried out in the present paper. Both of them showed a good agreement in accuracy between the obtained wave characteristics by the system and the observed ones.
