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Planning and Constructing Great-Circle Tracks, Continued
PIM
At this point in track construction, we have done everything except
determine PIM. Use the following step action table to determine PIM
and label the track. As an example, we will assume that the ship departs
at 10SEP1200Z and arrives at the straits of Gibraltar on 19SEP0700Z.
Step
Action
1.
Find the total hours available for the transit.
19 0700 = 18 3100
10
1200
10 1200
8 1900 = 8 days x 24h + 19h or 211 hours
2.
Add together all rhumb line distances between points A
through H. For our example, we’ll assume this to be
2247.5 nmi.
3.
Determine the overall SOA. 2247.5 nmi ÷ 211
hours=l0.65kn. Always round up to the nearest l/10 of a
knot. SOA = 10.7
4.
Begin with the departure point and lay out PIM times and date
in GMT for every 4 hours of transit time. Also label the time
of departure from each individual point. At this point we
have completed our track construction. As an aid to tracking
the ship’s progress it is highly recommended that the track
also be transferred to a small scale chart, as shown in figure
12-3.
Figure 12-3. Segment of overall track.
12-5
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