It is untrue to suggest
that traditional methods
of dead reckoning are no longer used as that is precisely what most
inertial navigation systems depend upon, except that they do it
However, plotting your DR
the old fashioned way
is a very simple system which, does not rely on any electronics or
With it you can quickly determine your present position by
course and speed from a previously known position.
It can also be used to determine your future position by
present course and speed from your present position.
DR positions should be
regular intervals depending on the nature of the passage.
They should be updated between fixes and changes in course or speed.
Of course it's important to remember that any direct reckoning
whether done electronically or manually is only an approximation as it
factor in tidal effects or leeway.
But by plotting the DR manually, as well as fixing your position with
will have a far better feel for where you are and how you are
Marine Chart Line Plotting In
my opinion your DR plots should be drawn
directly on to the relevant chart.
Some folk use 'chart
rather than writing directly onto their chart, personally I feel that
too prone to error and anyway it is easy to erase pencil lines provided
don't score them too heavily.
The first job is to draw
This is the preferred course from you starting position towards your
The starting point should be a fix such as the harbor entrance or a
marker which is shown on the chart.
Having drawn this you will now be aware of any possible hazards along
and the course required to avoid them.
It will also allow you
to work out the time
when you need to change course to avoid them.
How often you need to DR
along your rhumb
line will depend on where you are.
The closer to the coast and the more hazards there are, the more often
should DR and compare with the GPS information and if coastal sailing,
fixes taken from known conspicuous marks.
Running the DR along a
rhumb line will
quickly allow you to see if you are drifting off course.
The further you extend a
DR from a Fix the greater will
be the 'Circle of Error'.
While factoring in Set
and Drift will reduce
the size of the Circle of Error it should still be taken into
However, the more you
practice your Dead
Reckoning techniques the sooner it will become second nature and you
only gain confidence in your navigational ability but you will learn to
compensate for the errors.
"I loved cruising the coast of Maine. For one thing, it helped me conquer my fear of fog. Not that I have learned to feel secure in the fog, but at least I have learned how to grope without panic." (Herb Payson)
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