In predicting the Long-term distribution of random variables, such as ship's motion, ocean wave data of the area under consideration are indispensable. Such wave data are normally expressed in terms of significant wave height and wave period. North Atlantic Wave Data by Walden are very famous. If wave data of certain area are available, Long-term distribution of random variables of a ship on voyage the area is obtained by combining the said wave data and the energy spectrum of random variables. Some years ago authors proposed an approximate calculation method of Long-term distribution of a random variable by using c-value1). This time C-value is called wave data index. Wave data index can be calculated for each area where wave data are given and once wave data index is prepared, the Long-term distribution of a random variable in the area can easily be calculated by combining the index and the standard deviation of the random variables. In this paper the authors present the result of calculation of wave data index of North Pacific Ocean. Authors use the data published by Shipbuilding Research Association, Japan (SR) in 1980. 2) Its source data are stored at National Oceanic and Atomospheric Administration, U.S.A. and Japan Meteorological Agency. The authors calculated wave data index for each of them and the results are illustrated so that the readers can easily compare the sea roughness between areas or seasons.


development. Wave data are generally tabulated in terms of significant wave heights and average wave periods like Table l. But such tables are consisting of many figures and it is hard to tell, for example. from tables of two different areas, which is The prediction of long-term distribution of random variables related to ocean waves is very Important in undertaking ocean severer.

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