to transpcrb '■atex'iai as; 



-H •> k . l/'oh^ . L cos ■ 



wliai's h and 1 ars rr^up^ctively the heic^ht o-f tha v^ave and the lenf?t.b. 

 of the Travaj ,>, is the angle between ths dinjction of travsl of the 

 unbroken wave and the direction of travel of c-te deep-water wave' 

 (f.'hich is nearly ttie sarae as the direction of the vri.nd)| and k is a 

 coefficient 5 which is very close to a constant. As we do not kno^i' 

 either the height or the length of ths waves at different times j e„.^ = 

 over a year^ and as it is very difficult to measure them, we vrill 

 have to revert to the reason for the xvave, the wind. 



Although there is :'nuch material concerning the diinensions of 

 waves in relation to certain strengths of vrlnd over a certain length 

 of time, this question is in no respect solved. The observations that 

 we do have all point to the fact that the waves increase proportionate- 

 ly with the speed of the wind^ while the length and period increase 

 with the duration of the wind. There must also be considered another 

 factor which is of great importance in the creation of waves j, namely 

 what is called the "free space", or fetch of the wind. This is 

 understood to be the distance between a certain place on the coast 

 and the opposite coast, measured in the direction of the wind„ 

 (Figure /i). It seems obvious that the height of the waves must be 

 dependent upon the fetch, and experience proves that this is correct c 

 The largest waves, for the same strength of the wind, come from the 

 direction of longest fetch. There is not complete agreement about 

 how the length of the fetch, or free space is related to the size of 

 the waves, but most students are of the opinion that we must take the 

 free space into consideration since we cannot count on fetch distances 

 exceeding a certain maximum limit. This limit is not surpassed by 

 fetches from the coasts of the Baltic. However, on the west coast of 

 Jutland, which is exposed to northjirest winds which have free space 

 clear to Greenland, one should set the limit at about 1000 kilometers 

 (625 iTiiles) as one cannot count on steady winds for longer distances » 



On the basis of experience with the North Sea and Scottish lakes 

 VsF. Thomas Stevenson has set up the formula 



h = G -^ff 



where f is the free space in quarter-miles, and C is a coefficient 

 which for gales and great water depths (trochoidal waves) has the 

 value Oo4.5. On the Danish coasts it seems that G should have the 

 value 0.25 when f is measured in kilometers and h in meters » 



Following these considerations, we may substitute the following 

 expression for the previous formula for M 



!.T ^ G . S^ F V'f , cos oc 



where c is a coefficient, S the speed of the wind, and F the frequency 



