WAVES OF 

 THE SEA 



WIND WAVES 



Watching a passing "cafs paw" as it ruffles the sur- 

 face of a calm sea, you can see the first stage in the 

 formation of waves. As the wind grows stronger, 

 the ruffles grow into ripples ,and the ripples into 

 waves. Waves which are still growing under the force 

 of the wind are known as sea or wind waves. The 

 height and length of these waves are determined by. 



1. The fetch or distance over which the wind 

 is blowing. 



2. The average wind velocity over the fetch. 



3. The length of time the wind has been 

 blowing. 



In general, wind waves travel in the same direction 

 as the wind that formed them. Sometimes, if the waves 

 are still in the 'process of formation, the sea will be 

 choppy and difficult to describe. However, as the 

 waves grow under the influence of the wind, they 

 form themselves into a regular series of crests and 

 troughs at right angles to the wind direction. Their 

 length varies from about 12 to 35 times their height. 



SWELL 



When wind-raised waves travel out of a stormy or 

 windy area, they advance as swell and their form 

 undergoes a change. Their height decreases as they 

 advance, their crests become rounded, and their sur- 

 face smooth. Their length increases until it is gen- 

 erally between 35 and 200 times their height. 



Often you will find both sea and swell or two or 

 more systems of swell present in the same area. 

 Sometimes a system of wind waves travelling in the 

 same direction on top of a long low swell will almost 

 obscure the swell. However, the swell can usually 

 be felt in the roll of a heavy ship. In extreme cases, 

 the component may be so poorly defined that it is 

 impossible to separate them, and they can only be 

 reported as confused. 



wind woves 



swell 



