GPS. If the COG matches your desired
course then you are fine, and you carry
on, periodically checking that you do
not wander off course.
But more likely than not, especially
in our Pacific Northwest waters, when
you point the boat in one direction
you will not get a COG of exactly that
course. Chances are you will be set
to the right or left by tidal current, or
leeway, or both.
If your desired course is 200 M, for
example, and you find, while carefully
steering 200 M on the compass, that
your COG is actually 212 M, then you
are getting set to the right by 12°. The
job is to correct that, and the first guess
correction would be to turn 12° to the
left (steer 188 M) and then holding that
course carefully for a while check your
COG again. Now if your COG is 200M
then you have found your proper
course and that is the one you will
want to steer.
But before settling in on that one, it
will be best to over-correct for a while
to get back onto the original track line
you had intended. If you do not make
this correction you will be progressing
parallel to your intended track.
If you have current that is setting
you off course like this that requires a
correction, then it is most likely that
the SOG will be different from your
knotmeter speed as well. But this just
controls your rate of progress, not so
46 feet
much your safety. If your COG is wrong
you can get into trouble. The SOG just
14 days in the San Juans
tells you if you are getting into trouble
faster or slower than your knotmeter 2 happy boaters
speed.
One Bank
David Burch is the author of Modern Jennifer Patterson
Marine Weather and The Barometer Loan Representative
Handbook. He teaches online navigation
and marine weather courses at
Join me at the
www.starpath.com. He is a recipient of
Boats Afloat Show
the Institute of Navigation’s Superior
Jan. 29th - Feb. 6th
Achievement award for outstanding
on Lake Union
performance as a practicing navigator.
www.peoplesbank-wa.com/marine
5600 24th Avenue NW, Ballard • (206) 297
-
2850
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12/16/09 3:11:55 PM
a r y 2010 Pa g e 67
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