Gc) Rotate the template about the turning point until the Cj/C2 value
oorresponding to the contour interval being crossed intersects the tangent
to the midcontour. The orthogonal line on the ch art now lies in the direction crf the tumed orthogonal on the template (Figure 2-20 bottom);
W Place a triangle along the hase of the template and constiuct
a perpendicular to it so that the intersection of the perpendicular with
the incnming orthogonal is midway between the two contours when the distances are measured along the incoming orthogonal and the perpendicular
(See Point B in Figure 2-20 bottom). Note that this point is not necessarily rm the midcontmur line. This line represents the tumed orthogonal;
<(e) Repeat the above steps for successive contour intervals.
If the orthogonal is being constructed from shallmw to deep water, the
same procedure may be used, except that C2/Cj values are used instead of
c?sA template suitable for attachaient to a drafting •machine can be made,
Palmer (1957), and may make the procedure simplet if many diagrams are to
be used.
2.323 Procedure when a is Greater than 80 Degrees - The R/J Method. In
any depth, when et becames greater than 80 degrees, the above procedure
cannot be used. The orthogonal no langer appears to cross the contours,
but tends to run almost parallel to them.
In this case, the contour
interval must be crossed in a sériés of steps. The entire interval is
divided into a séries of smaller intervals. At the midpoint of the individual subintervals, orthogonal-angle turnings are made.
Referring to Figure 2-21, the interval to be crossed is divided into
segments or boxes by transverse Unes. The spacing R, of the transverse
lines is arbitrarily set as a ratio of the distance
between the contours. For the complété interval to be crossed, C2/C1
computed or
found from Table C-4 of Appendix C. ÇC2/C^t not
On the template (Figure 2-18), a graph showing orthogonal angle
turnings Aa, is plotted as a function of the C2/C1 value for varions
values of the ratio R/J. The Aa value is the angle tumed by the incoming orthogonal in the center of the subinterval.
The orthogonal is extended to the middle of the box, Aa is read
from the graph, and the orthogonal tumed by that angle. The procedure
is repeated for each box in sequence, until a at a plotted or intexpolated contour becomes smaller than 80 degrees. At this point, this method
of orthogonal construction must be stopped, and the preceding technique
for a smaller than 80 degrees used, otherwise errors will resuit.
2.324 Refraction Fan Diagrams.
It is often convenient, especially where
sheltering land forms shield a stretch of shore from waves approaching in
certain directions, to construct refraction diagrams from shallow water
2-73
oorresponding to the contour interval being crossed intersects the tangent
to the midcontour. The orthogonal line on the ch art now lies in the direction crf the tumed orthogonal on the template (Figure 2-20 bottom);
W Place a triangle along the hase of the template and constiuct
a perpendicular to it so that the intersection of the perpendicular with
the incnming orthogonal is midway between the two contours when the distances are measured along the incoming orthogonal and the perpendicular
(See Point B in Figure 2-20 bottom). Note that this point is not necessarily rm the midcontmur line. This line represents the tumed orthogonal;
<(e) Repeat the above steps for successive contour intervals.
If the orthogonal is being constructed from shallmw to deep water, the
same procedure may be used, except that C2/Cj values are used instead of
c?sA template suitable for attachaient to a drafting •machine can be made,
Palmer (1957), and may make the procedure simplet if many diagrams are to
be used.
2.323 Procedure when a is Greater than 80 Degrees - The R/J Method. In
any depth, when et becames greater than 80 degrees, the above procedure
cannot be used. The orthogonal no langer appears to cross the contours,
but tends to run almost parallel to them.
In this case, the contour
interval must be crossed in a sériés of steps. The entire interval is
divided into a séries of smaller intervals. At the midpoint of the individual subintervals, orthogonal-angle turnings are made.
Referring to Figure 2-21, the interval to be crossed is divided into
segments or boxes by transverse Unes. The spacing R, of the transverse
lines is arbitrarily set as a ratio of the distance
between the contours. For the complété interval to be crossed, C2/C1
computed or
found from Table C-4 of Appendix C. ÇC2/C^t not
On the template (Figure 2-18), a graph showing orthogonal angle
turnings Aa, is plotted as a function of the C2/C1 value for varions
values of the ratio R/J. The Aa value is the angle tumed by the incoming orthogonal in the center of the subinterval.
The orthogonal is extended to the middle of the box, Aa is read
from the graph, and the orthogonal tumed by that angle. The procedure
is repeated for each box in sequence, until a at a plotted or intexpolated contour becomes smaller than 80 degrees. At this point, this method
of orthogonal construction must be stopped, and the preceding technique
for a smaller than 80 degrees used, otherwise errors will resuit.
2.324 Refraction Fan Diagrams.
It is often convenient, especially where
sheltering land forms shield a stretch of shore from waves approaching in
certain directions, to construct refraction diagrams from shallow water
2-73