generated at the rough sea surface, until the net energy supply by 

 wind equals the energy losses by dissipation in the composite ocean 

 wave pattern. Until now, it has not been possible to observe a 

 continuous growth of certain waves after they have attained a cer- 

 tain height, length and maximum steepness. These waves broke heavily 

 in stormy weather and they did not disappear or increase when the 

 fetch increased or the duration of wind became longer. But when ex- 

 ceeding a certain fetch longer and flatter waves rather soon emerged 

 at this rough sea surface with its steep wave motion, and these waves 

 probably grew independently of the rough sea as individual waves. 

 The superposition of these longer waves with a phase velocity great- 

 er than the wind velocity, and the characteristic "sea" with a phase 

 velocity smaller than the wind velocity finally led in the fully de- 

 veloped sea to significant fluctuations of wave periods (time inter- 

 vals between succeeding crests at a fixed place), heights, and to 

 the occurrence of outsize waves, groups of waves and other phenomena, 

 as described in Chapter I. 



This first attempt to consider the growth of complex ocean 

 wave motion under the action of wind, and the ideas involved in 

 theoretical calculations are based to a large extent on observations 

 and on empirical relationships. Both of them are incomplete today, 

 and it is quite possible that more comprehensive information on 

 complex sea wave motion in the future will lead to better approxi- 

 mations and theoretical treatments. This approach does not claim 

 to have the desirable completeness. At present, it seems that we 

 are still rather far away from a complete understanding of the prob- 

 lems of ocean wave generation and behavior. At any rate, it seems 



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