Boating and Sailing.pdf - Moja ladja

In compasses, bigger is better. The larger the
compass card, the easier it is to read and the
more accurately you can follow a course. Larger
compasses cost more but are worth the investment
in boats run regularly out of sight of land.
Variable Variation
Compasses point to magnetic north, but meridians
on a chart are laid out relative to geographic north.
The difference between the two is known as variation.
Variation is a compass error resulting from the
fact that magnetic north and geographic north are
not identical directions on most parts of the earth.
Chapter 13: Tools and Tricks of Navigation
For short voyages and in some locations, variation is insignificant. For longer journeys
and in other spots, particularly in more northern latitudes, it can be very significant.
Variation approaches 20 degrees along the coasts of Maine and Washington, and 10
degrees along the California shore. On a long coastal voyage, that much alteration in the
course could put you hundreds of miles off course, run you aground, or get you lost for
days.
The error introduced by variation is westerly on the East Coast and easterly on the West
Coast. Thus, easterly errors are added to the true course you wish to follow as laid out on
a chart, and westerly errors are subtracted.
For example, if you want to follow a course of 45 degrees true—that is, relative to the
geographic north pole—along the coast of Maine, you would have to add about 16
degrees, the variation in that area, to the magnetic course shown. It looks like an Algebra
II equation, but it’s simple addition or subtraction:
45T + 16W = 61M
In this simple equation, T stands for the true course (one accurately measured in relation
to the geographic north pole, with corrections made for variation and deviation of the
compass), W stands for the variation or compass deflection to the west from true north
caused by the location of magnetic north, and M stands for the magnetic course, or the
compass course you would steer to adjust for or “compensate” for the variation.
So, to travel 45 degrees true in that area, you’d steer 61 degrees on the compass.
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Boat Bytes
A bit of old mariner’s
advice is also worth
remembering: If you’re on
Florida’s side of the Gulf of
Mexico or on the Pacific
Coast and you start to head
home at sundown but the sun
is in your eyes, turn around.
Nature’s clues are never
wrong—stay attuned to them.