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Plotting Instruments
Basics
Let’s put together what we’ve learned about the DR plot, the tools of the
trade, and the techniques the Quartermaster uses.
Tools used to project lines, scribe arcs, measure angles and distances,
and do a host of other jobs are just some of the hand tools you will use
as a Quartermaster. Items such as pencils, parallel rulers, compasses,
and dividers are a MUST on any bridge or in any chart room.
Tools of the
Trade
Pencils: Primary among these tools is the pencil you use. There are
several grades or hardness of lead. The softer grades, such as the No. 2,
are ideal for plotting positions on the chart and for other general uses
around the bridge. No. 3 pencils are considerably harder, will hold a
point longer, and will usually sharpen better for use in drawing fine
lines as will be required when the QM wants to plot stars, draw course
lines, or do other chart work that requires the use of better than average
lines to show the condition to be depicted. Under most conditions, only
the Nos. 2 and 3 grade pencils will be necessary.
Parallel Rulers: Parallel rulers are instruments used for moving lines
parallel to themselves, determining direction from the compass rose, and
laying out course lines.
These are, of course, only a few of the uses of
parallel rulers.
Some of the other uses include drawing straight lines,
advancing lines of position, checking ranges, plotting fixes, and
measuring direction from one given point to another. There are other
devices available which are easier to use and will do the same job as
parallel rulers.
The Weems parallel plotter (fig. 8-7) is the most widely
used variation of the parallel ruler.
Figure 8-7. A parallel rule (top) and a Weems parallel plotter.
8-13
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