and suitably spaced orthogonals are drawn perpendicular to this wave front 

 and parallel to the chosen direction of wave approach. Closely spaced 

 orthogonals give more detailed results than widely spaced orthogonals. 

 These lines are extended to the first depth contour shallower than L^/2 

 where L^ (in feet) = 5.12 T^. 



TABLE 2-2 EXAMPLE COMPUTATIONS OF VALUES OF 

 Cj/C2 FOR REFRACTION ANALYSIS 



Column 1 gives depths corresponding to chart contours . These 

 would extend from 6 feet to a depth equal to L /2 . 



Column 2 is column 1 divided by L^ corresponding to the given 

 period. 



Column 3 is the value of tanh 27rd/L found in Table C-1 of 

 Appendix C, corresponding to the value of d/L^ in 

 column 2. This term is also C/C^^. 



Column 4 is the quotient of successive terms in column 3. 



Column 5 is the reciprocal of column 4. 



2.322 Procedure when a is Less than 80 Degrees . Recall that a is the 



angle a wave crest makes with the bottom contour. Starting with any one 



orthogonal and using the refraction template in Figure 2-18, the following 

 steps are performed in extending the orthogonal to shore: 



(a) Sketch a contour midway between the first two contours to be 

 crossed, extend the orthogonal to the midcontour, and construct a tangent 

 to the midcontour at this point. 



(b) Lay the line on the template labelled orthogonal along the in- 

 coming orthogonal with the point marked 1.0 at the intersection of the 

 orthogonal and midcontour (Figure 2-20 top) ; 



2-71 



