Boating and Sailing.pdf - Moja ladja

Chapter 11: Nautical Road Maps: Marine Charts
LORAN lines, which are slightly curved, are also shown on many charts, although
LORAN is gradually being phased out by GPS. By reading coordinates from two towers,
the LORAN machines provide exacting navigation, usually to within 100 yards. For more
on this system, see Chapter 13, “Tools and Tricks of Navigation.”
GPS, Global Positioning Systems, allow you to pinpoint your location via latitude/
longitude information received from satellites. The system works almost worldwide.
We’ll learn more about its use in Chapter 13.
The Compass Rose
The compass rose is a direction-indicator printed at several locations on most charts. It’s
used in laying out compass courses. The “rose” is a circle about the diameter of a grapefruit
printed on the chart, aligned with true north toward the top. It’s printed in a reddish
maroon ink, thus the “rose” designation.
The circle is divided into 360 degrees. There’s a second circle within the outer circle, also
divided into degrees. This inner circle is an indication of magnetic north, which moves
around as much as a sitting president’s politics, left one day, right the next.
Look closely and you’ll note that the inner circle doesn’t show exactly the same “North”
as the outer circle. Does this mean mapmakers are afraid to make a decision? No. But it
does indicate something even more unsettling, which is that the magnetic poles of the
earth are in motion! Don’t call Arthur C. Clarke on this one. It’s been going on for a very
long time and nobody is concerned.
By use of parallel rules, you can measure the direction of a course you want to follow from
this rose. Line up the course, and then walk the rulers to the nearest rose and run one
through its center to get the course.
If you’re not going far—say you’re in a shallowdraft
boat and you’re heading toward a large, visible
landfall such as a lighthouse—the common
method is to look at the compass rose, estimate
the direction as, say north-northeast, and head in
that direction. That way, if rain or fog moves in
before you get there, you can still hold course via
the compass.
For longer voyages in deep draft vessels or when
you need to find a small object such as a navigational
buoy, it’s standard operating procedure to
use the parallel rules and the compass rose to compute
an exact course.
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Boater-ese
Parallel rules are two
pieces of clear plastic connected
by swiveling arms that allow
them to be “walked” across a
chart while maintaining a measured
angle. See Chapter 14,
“Nautical Radio Gear and
Procedures and Your First Longer
Cruise,” for details.