Abstract 



Sea state forecasts are based on a combination of empirical 

 knowledge and theoretical relationships of wind and ocean waves. 

 Because the sea surface wave pattern usually consists of a locally 

 produced sea and superimposed swell) two separate procedures of fore- 

 casting are necessary, both generally based on oceanic weather maps: 

 forecasts of waves generated by the direct action of wind, and sea 

 swell forecasting. After combination of these two Independent pheno- 

 mena, one may estimate the actual state of the sea surface pattern 

 at a given locality. 



Chapter I of this report communicates some results obtained by 

 observations on the composite nature of wind generated waves. The 

 characteristics of dominating waves in the fully developed state at 

 different wind velocities are discussed. 



A conspicuous feature of the rough sea is the phenomenon of 

 interference. Observed periods, lengths and heights of waves vary 

 through wide ranges, and in this complex wave motion outsize waves 

 occur, as a consequence of interference patterns. An attempt is 

 made to explain some striking features of composite wave motion by 

 principles of interference. 



Chapter II deals with the growth of the dominating waves. Re- 

 lationships are derived between the waves, the wind velocity and the 

 area of water over which the wind blows (fetch), or the length of 

 time that the wind has blown (duration). The numerical application 

 of these relationships requires the knowledge of the amount of 

 energy available for the growth of waves under various conditions. 

 In this report a first attempt Is made to estimate the difference 



