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I would say that the biggest problem with GPS it that it is a single
system that is so reliable that it is easy to forget it will not always
be there.

In pre-GPS coastal navigation from my era we had Loran-C, radar, RDF,
pelorus, gyro-compass, sextant, and the depth sounder. Radar was the
most popular as it gave you an instant range/bearing fix as long as some
prominent bit of land was in range. Loran-c was great when it worked,
but we spent a lot of time getting information from half the chain.  The
sounder was really handy when you crossed an obvious sounding line. I
used the sextant for distance off calculations. The RDF was occasionally
used, but no single piece of equipment was ever the single source of
data.

GPS does have it's faults, other than total failure. As in lightning
strikes. It is not reliable in the high north. It is also subject to
political failure. A fellow Captain in my 60 Ton course was at sea at
the time of the 911 attacks and said that GPS was all over the place for
several hours during that time. Civilian GPS is easily jammed with very
little power and unsophisticated equipment.  A malfunctioning home TV
antenna booster shut down GPS in a harbour in the US. The leaky signal
took a long time to trace as the transmissions apparently bounce off
everything. That little bit of stray EM radiation made the GPS
unreliable for a five mile radius. If I can find the article again I
will post it here.

I will happily admit that I would never take a serious voyage without a
good chart plotter, and two spare GPS units tucked in ziplocks with
spare batteries. Besides, they work in the fog! Roz Savage used her Tom
Tom when her plotter packed it in on her rowing voyage from San
Francisco to Hawaii.


"Jamming in Moss Landing Harbor, CA
15 Apr 01 - 22 May 01, VHF/UHF television antenna with pre-amplifier
caused GPS failures to all of Moss Landing Harbor
Boat owner purchased TV antenna, which was equipped with pre-amp
 From interior location Amp's emitter jammed all of Moss Harbor and
1km out to sea
No GPS in entire area = 37 days
Impact to Moss Harbor
Research vessels relied heavily on timing from GPS
Extreme difficulty going through harbor in foggy conditions
Notification to all vessels in area that GPS was down

Keep a good watch

Bruce Hamilton


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