Radiobeacons
Radiobeacons were first introduced in few marine radiobeacons are still operational
U.S. waters in the 1930s as an aid to coastal and marine radio direction finders are more
navigation. Onboard receivers with direc- likely to be found in antique stores than on
tion-finding capabilities could indicate the boats. Despite this, many charts still indicate
bearing to a transmitting beacon. Today, very radiobeacons that are no longer operational
or are used exclusively by airplanes.
Depth Sounders
Depth sounders are often overlooked as a time on top of charted contour lines and
navigational tool. align them. This technique works best when
Ocean bottom features are similar to you’re crossing contour lines at sizable angles.
topographical features on land. Bathymetric Electronic depth sounders use a type of so-
charts based on systematic surveys show nar to measure depths. To address the needs
these features as bottom contours alongside of commercial fishermen, depth sounders
continents and along heavily traveled routes have grown dramatically more sophisticated
between continents. Using a good depth in recent years. Sonar arrays not only deter-
sounder, you can detect when you’re passing mine depth, but can also provide detailed
over a prominent feature like a seamount or outlines of bottom contours, bottom com-
canyon. In the absence of such features, you position, thermoclines and schools of fish.
can overlay a trace of soundings taken over
ts
LORAN-C
Despite the dominance of GPS, LORAN-C Time differences received from two or more
remains a useful navigation system along the pairs of towers provide a fix.
Eastern and Gulf Coasts of North America. Although LORAN can convert the time
RAN/Char
It is of some utility in the northern regions differences into latitude and longitude, for
of the Caribbean. Ground wave coverage the best use of LORAN-C, you should obtain
L
O
extends from Newfoundland to Texas, and charts with a LORAN grid overlay. Plotting
from the northern Bahamas to Cuba and on LORAN Time Differences (TDs) on these
to the Gulf of Honduras. Many users report charts is more accurate than using the lat/
fading signals and poor accuracy as they ap- long data generated by the receiver. TDs have
ion
proach Bermuda. proven more accurate than GPS in terms of
gat
At press time, the future of LORAN was returning to the same position of a previous-
undecided. The LORAN system has been ly recorded LORAN reading. Most receivers a
v
i
extensively upgraded in the last few years, can store TD waypoints.
N
and in the spring of 2007, the Coast Guard Skywave coverage is much less accurate
announced that Loran-C will continue “for and is subject to false readings. Skywave fixes
the short term,” without elaboration. LO- must be used with great caution and should
RAN works by using pairs of radio broad- be confirmed with other navigational means.
casting towers emitting timed signals. The Current Loran-C status reports and a list
LORAN receiver calculates the difference in of the LORAN towers are available from the
time between the receipt of the two signals U.S. Coast Guard’s NAVCEN.
to determine its location between the towers.
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