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variation or declination changes by as much as 20 degrees
in the circumnavigation of the Earth.
Mariners have also been influential in tracking the Earth’s
movements through their charts. Portolon charts were created
in the 1300s in Genoa by creating rhumb lines (or loxodomes)
that radiated from the center of the chart in the
direction of the wind or compass points and were used by
mariners to plot their course from one harbor to another.
These rhumb lines were the precursor to our compass rose.
A chart from 1940, at left, shows that the variation in magnetic
north in New Orleans was 6 degrees 20 seconds
East with a change of 1 second per year. The annual increase
or forward yearly variation in 1960 was 3 seconds.
If the 1960 chart made an accurate prediction 41 years
forward to 2011, the difference between true north and
magnetic north should be 4 degrees 17 seconds West.
The actual variation on a 2011 chart is 0 degrees 14 West,
a possible error of 3 degrees 58 seconds, which translates
to missing the New Orleans sea buoy on a 100 nautical
mile trip North by about 7 miles. This is significant. This
difference is a direct result of 2,890 to 5,150 kilometers
of electrically-conducting molten iron that runs erratically
with temperatures hotter than the surface of the sun.
The drift of the magnetic North Pole has very little effect
on most human life. But for anyone that depends on charts
and a compass, this drift, if not calculated properly, can
mean the difference between being adrift and on course.
Global positioning systems (GPS) may fail through a lightning
strike or in times of war, but a mariner’s knowledge of
charts and compasses will always hold you in good stead.
Practice your dead reckoning skills using a magnetic course
with variations taking into account local disturbances (iron
on the boat, etc.), your direction of drift, set and speed.
Check your charts for accuracy of variation. That old chart
from 1940 might not be the best backup system. Remember,
the great thing in this world is not so much where we
stand, as in what direction we are moving.
Fair winds and calm seas…
Captain Ted Sputh holds a USCG and MCA, 3000 Ton,
Upon All Oceans with Sail license and has been a professional
mariner for 33 years. He is currently doing relief and
delivery work. Contact him at ted@captainteds.com.
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