deptho The vertical scale is oc } the angle between the wave crests in 

 deep water and the bottom contours „ 



The solid curves are lines of equal »= s the angle between the wave 

 crest and the depth contour at any relative depth„ When the period and 

 angle in deep water are known, these curves are used to obtain the angle 

 of the waves at any given deptho 



The dashed curves are lines of equal K, the correction factor to be 

 applied to the wave height in deep water to get the wave height in shallow 

 water o 



Surface Wave Heights from Under-water Pressure Measurements; Plate 

 15 gives the factor for computing surface wave heights from data taken by 

 under-water pressure measurements For a pressure unit located at a 

 distance of g below the surface in a total depth of water D where waves of 

 length L exist, Plate 15 gives the value of the pressure response K, which 

 is defined as the ratio of the head of the pressure fluctuation at the 

 submerged point, to the surface wave height „ 



Forecasting of Wind Waves and Swell ; Plate 16 is used to determine 

 whether fetch or duration is the limiting factor for wave characteristics 

 at the end of the fetchu The graph is- entered with the duration (in 

 hours) and the wind velocity (in knots) and the corresponding minimum 

 fetch length read off from the lines of constant fetch (thus a duration 

 of 36 hours and a wind velocity of 35 knots gives a minimum fetch length 

 of 4.00 nautical miles) „ If the actual fetch is less than this minimum 

 fetch, then fetch is the limiting factor, and an equivalent duration is 

 selected; if the actual fetch is greater than this minimum fetch, then 

 duration is the limiting factor » The latter is the usual case., 



Plate 17 or 18 is used to determine the wave characteristics at the 

 end of the fetch from the duration selected from Plate 16 « The graph is 

 entered with the duration (in hours) and the wind velocity (in knots), 

 and the corresponding wave heights and periods read off from the lines of 

 constant height and period „ (Thus' a duration of 36 hours, and a velocity 

 of 35 knots gives a corresponding wave height of 25 feet, and period of 

 10 seconds at the end of the fetch*) 



Plate 19 can be used to determine the wave characteristics at the 

 end of the fetch when fetch is the limiting factor or when an equivalent 

 fetch has been selected „ The plate is entered into the fetch length (in 

 nautical miles) and the wind velocity (in knots) and the corresponding 

 wave height and period read off from the lines of constant height and 

 period „ (Thus a 100 mile fetch and a 35 knot wind give a wave height of 

 19 feet and period of 6„7 seconds at the end of the fetch ») 



Plate 20 is used to determine the wave characteristics at the end of 

 the decay area The graph is entered with the decay distance (in nautical 

 miles) and the period at the end of the fetch (as determined from Plate 

 17, 18 or 19) and the corresponding height ratio, period, and travel time 

 read off from the lines of constant value (Thus a decay distance of 

 1000 miles and a 12 second period give a height ratio of 0»47, a period 

 of 16 seconds, and a travel time of 4-1 hours ») The period at the end of 



