On the Prediction System of the Ship Motion for Ship Routing

Abstract

For increasing the safety of a ship voyage, the right information should be offered to a ship's master on her safety affected by environmental conditions such as meteorological and sea state which will be foreseen to be encountered as the ship route is determined. This paper presents a prediction system of ship motion from this point of view. To use this system effective, some experimental computations must be made by a crew himself for various conditions, and so this system is designed to use a shipborne computer. From the prognostic weather map recieved by a facsimile, read a pressure pattern around the wide area where the ship will be, guess a wind field to be, and compute the wave spectra, then evaluating the ship motion from these spectra. These spectra are treated as the sum of the wind sea spectra determined from the narrow time-space information and the swell forecasted from the wide time-space information. The region where the evaluation of ship motion is predicted is bounded by the range which the ship runs before and after 12 hours from the prediction time, and by the sector lies between ±30°from the planned ship's route. The ship motion is cvaluated as the sum of a roll and a pitch, both multiplied by appropriate evaluation coefficients respectively. Morever, these coefficients are to be chosen whether a roll is more important or a pitch due to a route and a type of a ship. The problem which appears in constructing this system's hardware is the input and output parts; man-machine communication part. On the input part, a coordinate reading equipment is developed to read the data from the weather map. As the output part, X-Y plotter is used to express the result in a intuitively clear way. The example obtained by this system is shown as Table 1, and the results are obtained quite satisfactorily in spite of the relatively rough approximation in the software design.