44 



Observations and Measurements of Ocean Waves 



simultaneous observations of wind velocity and wave height have been used 

 to derive a mathematical relation between both values. Difficulty is that 

 the wind velocity is evaluated after the Beaufort-scale, and the reduction 

 of the values to m/sec is different according to the different observers and, 

 therefore, the observations are not always comparable. Another difficulty 

 is that very often the force of the wind is measured at deck height of the 

 ship and is different from the wind acting on the ocean surface. For this 

 reason, it is not surprising that the relations between the wind velocity v 

 (m/sec) and the wave height h (m) have shown variations according to the 

 different observers. Therefore, we will obtain a relation derived by Cornish 

 h — 0-37v which mathematically is not exact, but is rather a rule which tries 

 to represent average conditions. 



This equation assumes that for a given wind velocity with a sufficient 

 duration, and if the fetch is long enough, there is a definite maximum wave 

 height. 



We will discuss in another chapter the growth of the waves and the 

 experiments which determine the relation between the wave height and the 

 duration of the wind action (see p. 87). Table 5, by Cornish shows the 

 values of the different characteristics of a wave in relation to the wind velocity. 



Table 5. Maximum dimensions of waves relative to wind force 



(According to V. Cornish) 



Table 6. Relation between wind force and wave height 



(According to E. Zimmerman) 



Table 6, by Zimmermann in 1914, is an analysis of 143 values of the 

 relation between wave height and wind velocity. It gives the average values 



