Exaiiipl e 



a. Wind velocity from current map .... 32 knots 



b. Wind velocity 21+ hours earlier .... 20 knots 



c. Average wind velocity for last 12 hours 



(a - ^) 29 knots 



d. Maximuia wave height 24 hours earlier 



( f roin preceding map) 10 feet 



e. Time needed by 29-knot wind to raise 



10-foot waves (Plate IV) 7| hours 



f. Duration of 29-knot vdnd (24 hours +e) . . 32 hours 



Determination of Highest Wind Waves (11,12) 



When wind velocity, fetch, and duration have been determined 

 the minimuiu duration (10) is read off from Plate I. If the dura- 

 tion is longer than the minimura duration the wave height and vrave 

 period at the end of the fetch are obtained from Plates II or 

 III, if it is shorter, from Plates IV or V. 



Example 



Wind velocity 29 knots, fetch 800 nautical iiiiles, duration 32 hours 



From Plate I: minimum duration, 43 hours. 

 From Plate IV: wave' height, 18.0 feet, 



wave period, 9-0 seconds. 



Determination of the Swell (13-20) 



1. Waves advancing through regions of calm . The distance of 

 decay (the distance from the end of the fetch to the locality for 

 which the forecast is made) is measured on the map. Entering Plate 

 VI v/ith the distance of decay, D, and the period at the end of the 



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