G /C should hs ca3-culabed for orthogonal construction from deep 



to shallc-r water. 

 G /C should be calculated for orthogonal construction from 



shallovr to deep water. 



31, To construct sn orthogonal fror: deep to shallo-r :;ater, a deep tj-ater 



direction of wave approach is first selected hj a hindcastins study of 



historical weathsr charts, by fan diagran analysis (see pajragraph 38) or by 



direct observation. A deep i.-ater irave front (crest) is dratm a^ a straight 



line perpendicular to this wave direction siid stdtably spaced parallel lines 



(orthogonals) are drawn frora this wave front in the chosen direction of wave 



approach. These lines are extended to the fii.rst denth contour shoaler thaji 



l/'2 L where L = 5.12t2, 

 ^ o o 



32» Proce dures for a less than 80 , - Starting id-th any one orthogonal, 

 the fo3.1ox-jing steps should i3e taken: 



(a) Sketch in a rd.d-contour bet-ween the first two contours to be 

 crossed, e^ctend the orthogonal to this raid-contoujr, and construct a tangent 

 to the riiid-contour at tliis point: 



(b) Lay the line labelD.ed. "orthogonal" along the inconiing orthogonal 

 T-rith the point marted 1^.0 at the intersection of orthogonal and raid-contour, 

 (see Figure 13 a); 



(c) Rotate the template about the "turning point" until the S-,/^p 



values corrosponding to the contour interval being crossed intersects the 

 tangent to the liiid -cent our = The "orthogonal" line now liss in the direction 

 of the turned orthogonal. (See Figure 13b); 



(d) Place a triangle along the base of the plotter and erect a 

 perpendicular to it so that the intersection of this perpendicular with the 

 incoining orthogonal is equidistant frora the two contours liieasured along the 

 incOTiUng orthogonal aaid tliis perpendicular . This line represents the tui^ned 

 orthogonal; 



(e) Repeat the process for the neict contour intervals < 



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

 the same procedure is followed, except that G^/C^ values are used instead 

 ofG^/C^. 



314. c Procedures for a greater than 80 . - In any depth of water, xrlTsn 

 a becomes greater than 80°, the above procedures may not be used* The 

 orthogonal no longer appears to cross the contours, but tends to run parallel 

 between then;. In this case the contour interval is crossed in a series of 

 steps. In essence, tha whole interval is divided into a series of smaller 

 intervals, at the rn.d-points of which, orthogonal angle turnings are made. 



22 



