TO DEEP WATER 



WAVE CRESTS 



\ 



FINAL 

 POSITION 



INJTIAL POSITION 



Figure 9. 



deep water and crest 14, thus, the points on crest 

 14 which are midway between orthogonals A-L 

 (fig. 7) have been transferred to figure 6. It has 

 not been necessary to carry orthogonal /, seaward 

 from crest 14 as orthogonals H and J give a 

 measure of the refraction for this portion of the 

 wave. 



As an example of the computation of the re- 

 fraction coefficient, K^, a point on the 5-fathom 

 contour midway between orthogonals K and L is 

 considered. The procedure is as follows: 



On chart 5403 (fig. 7) the distance between 

 orthogonals K and L at the 5-fathom line is 

 2.9 inches and at crest 14 the distance is 1.72 

 inches. 



On figure 6 (chart 5402) the distance be- 

 tween orthogonals K' and L' is 0.49 inch at 

 crest 14 and 0.12 inch at crest 1. Therefore, 

 the refraction coefficient for the point mid- 

 way between orthogonals K and L at the 

 5-fathom line is: 



K, 



=vs 



.7^ 02 

 9 ^0.49~"-"*^ 



Computations for refraction coefficients at 

 other points along the 5-fathom contour are 

 summarized in table 3. To obtain a refrac- 

 tion coefficient for a point nearer to the 

 Municipal Pier than obtained by orthog- 

 onals A and B, additional orthogonals have 

 been drawn on charts 5403 and 5415 (fig. 8). 

 Point M on crest 23 has been selected as a 

 starting point. On chart 5403 two orthog- 

 onals, 0.3 inch on either side of point M, 

 have been carried seaward to crest 17 in 

 deep water, where the distance between 

 orthogonals is 0.13 inch. On chart 5415 the 

 two orthogonals, 1^ inches on either side of 

 point M, have been carried to the 5-fathom 

 contour where the distance between orthog- 

 onals is 4.72 inches. The value of K^ at 

 this location on the 5-fathom contour, which 

 is 0.8 nautical mile from the Municipal Pier, 

 is 



K, 



VI 



13 ^__ 

 6 ^4.72" 



^0.37 



For the benefit of the forecaster, refraction dia- 

 grams should be prepared for various periods and 



13 



