FIND: The wave height at a point P having coordinates in units of wave- 

 length of X = 3 and y = 4. (Polar coordinates of x and y are r=5 at 53°.) 



SOLUTION : 



Since dg = 15 feet, T = 8 seconds, 



Using Table C-1 with 



the corresponding value of 



d d, 



- or — = 0.0899 , 

 L L 



therefore. 



d. 



(V. 



= 167 feet 



0.0899 



Because 1 inch represents 133 feet on the hydrographic chart and 



L = 167 feet, the wave-length is 1.26 inches on the chart. 



This provides the necessary information for scaling Figure 2-36 to the 



hydrographic chart being used. Thus 1.26 inches represents a radius/ 



wavelength unit. 



For this example, point P and those lines of equal K' situated 

 nearest P are shown on a schematic overlay. Figure 2-41. This over- 

 lay is based on Figure 2-36 since the angle of wave approach is 135 . 

 It should be noted that Figure 2-41, being a schematic rather than a 

 true representation of the overlay, is not drawn to the hydrographic 

 chart scale calculated in the problem. From Figure 2-41 it is seen 

 that K' at point P is approximately 0.086. Thus the diffracted 

 wave height at this point is 



H = K'H,. = (0.086) (10) = 0.86 foot say 0.9 foot . 



The above calculation indicates that a wave undergoes a substantial 

 height reduction in the area considered. 



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2-96 



