Personal computers can run a wider variety
Updating Electronic Charts
of charting applications (both raster and vec-
Currently, many electronic chart suppliers
tor), can be connected to other electronics,
are providing update services. Via regularly
and of course offer all the other advantages
scheduled emails and downloads, users are
of a PC. But PCs tend to be heavy electrical
sent electronic patches that either correct the
consumers, are comparatively delicate pieces
chart when it is displayed on the computer, or
of machinery and can be prone to crashing,
alter the chart file to reflect any corrections.
often at the most inopportune times.
If the electronic charts you are using don’t
Using Electronic Charts provide this service, it’s critical to ensure you
Good electronic charts and charting soft-
have up-to-date charts. Many programs will
ware can make it extremely easy to establish
allow you to add text and drawings onto a
waypoints, plan routes, avoid hazards and
chart, and you can use this method to note
perform general navigation tasks. As with
relocated buoys, new soundings, and so on.
any electronic navigation tools, it is impor-
Chart Datums
tant to remember that the computer is not
A geodetic datum is the basis on which a
the navigator.
chart is drawn. Today, nearly all U.S. charts use
The biggest value of an electronic chart is
the WGS 84 datum, but older charts covering
that, when combined with input from a GPS,
more remote areas may use a different datum.
you can see your position at a glance and
Pay attention when transferring a naviga-
track your progress across the chart in real
tional plot to an adjacent chart with a dif-
time. This has lead many new navigators to
ferent geodetic datum, or when transferring
treat their electronic chart as a sort of video
positions from one chart to another chart of
game, ignoring information from other
the same area that is based upon a different
sources. It is important to keep your eyes
datum. The transfer of positions should be
open and your brain focused on what is hap-
done by bearings and distances from com-
pening in the world beyond your navigation
mon features.
station. An electronic chart will not display
Be sure to read chart notes carefully. Notes
other vessel traffic, nor is it a perfect repre-
in connection with chart title include the
sentation of the real world.
horizontal geodetic datum that serves as a ref- adar
All the navigational techniques discussed
erence for the values of the latitude and longi-
R
under GPS apply to electronic charts, which
tude of any point or object on the chart. The
generally make the tasks easier. Particularly
latitude and longitudes of the same points
on a PC, electronic charts allow you to es-
or objects on a second chart of the same area
tablish endless waypoints and routes fairly
that is based upon a different datum will dif- ion
easily before you even get underway. Many
fer from those of the first chart. The differ-
dedicated chart-plotters can connect to a PC,
ence may be navigationally significant.
which allows charts, routes, waypoints and
It is particularly necessary to note the chart
other information to be stored on the com-
a
v
i
gat
datum when using the Global Positioning N
puter and uploaded to the chart-plotter’s
System (GPS). Some features, such as iso-
limited memory.
lated islands, may be as much as several miles
from their charted location, especially if the
chart has been produced from older surveys.
Radar
Many mariners feel that radar is the most
The transmitter sends out a very short
versatile electronic navigation aid when sail-
pulse of powerful electromagnetic energy
ing along the coast. It not only gives position
from the antenna in a narrow, horizontal
information but also indicates the dangers of
beam at the speed of light (300 million me-
collision by tracking other vessels.
ters/second).
Radar consists off four basic components:
The horizontal width of the beam is de-
transmitter, antenna, receiver, and display.
termined by the size of the antenna. Larger
antennae produce smaller horizontal beams.
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