Table 2-2 



Example computations of values of C /C„ 

 for refraction analysis.^ 



^Column 1 gives depths corresponding to chart 

 contours. These would extend from 2 meters to a 

 depth equal to Lq/2. Column 2 is column 1 divided 

 by L corresponding to the given period. Column 3 

 is the value of tanh2iTd/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) Lay the line on the template labeled orthogonal along the 

 incoming orthogonal with the point marked 1.0 at the intersection of 

 the orthogonal and midcontour (Fig. 2-20, top). This establishes the 

 turning point. 



(3) Rotate the template about the turming point until the C /C 

 value corresponding to the contour interval being crossed intersects 

 the tangent to the midcontour. The orthogonal line on the chart now 

 lies in the direction of the turned orthogonal on the template (Fig. 

 2-20, bottom). 



(4) Place a triangle along the base of the template (this edge 

 should be parallel to the line through the turning point) , and con- 

 struct a line parallel to the template orthogonal line so that it 

 intersects the incoming orthogonal at point B. This intersection 

 point is to be equidistant along the incoming and turned orthogonal 

 lines (see insert to Fig. 2-20 ,b where AB = EC). This intersection 

 point is not necessarily on the midcontour line. 



(5) Repeat the above steps for successive contour intervals. 



If the orthogonal is being constructed from shallow to deep water, the 

 same procedure may be used, except that C /C values are used instead of 

 C,/C,. 



A template suitable for attachment to a drafting machine can be made, 

 (Palmer, 1957) and may make the procedure simpler if many diagrams are to be 

 used. 



2-68 



