Life
without
Loran
Life
without
Loran
What are the options if
GPS goes down?
The recent shutdown of the Loran-C system has drawn a great deal
of criticism from many in the marine industry. What follows is a
fictional account describing the action aboard a boat when GPS goes
down and there is no backup to take its place.
PREVIEW
The Panamanian cruise ship Royal Majesty was on course to Boston on
June 10, 1992, when it grounded on Rose and Crown Shoal 10 miles
east of Nantucket Island. The primary technical cause of the grounding
was determined to be the undetected loss of the GPS guidance signal to
the ship’s autopilot. The vessel had been proceeding under GPS-aided
autopilot control for some 34 hours prior to the accident. The bridge
watch was not following the traditional practice of using at least two
independent sources of position information. GPS was considered
sufficient. Fast forward to the present.
We are 40 miles northeast of Mon- tauk Point, Long Island, NY, des- tination Mystic, CT. Like the Royal Majesty, our vessel is pro- ceeding on autopilot and has been precisely tracking the intended course for many hours. Unlike the
system on the Royal Majesty our GPS/autopilot has a
loss of GPS guidance alarm function and we’ve been
noting our vessel’s track on the chartplotter. It’s a beautiful night, black as pitch but with an unusual light in
the northern sky. Everything is in order when the GPS
fail alarm sounds. The autopilot switches to its heading
mode and we begin to troubleshoot the problem.
A check of the back-up GPS confirms the GPS signal
loss message on the autopilot control screen. We power
up the handheld, battery-powered GPS and after a couple of minutes are convinced that for the moment at
least there is no GPS signal.
We have an experimental navigation receiver on loan
from the manufacturer that’s capable of receiving signals
from GPS, the few Galileo satellites already in orbit, the
Russian GLONASS birds and even the Japanese Compass satellite. Unfortunately, a check for signals confirms
that there are no usable signals from any of these satellite sources, only noise, massive amounts of noise. Time
to go for plan “B”—proceed using any and all of what
the Coast Guard calls “legacy” aids to navigation—
floating and fixed.
Back to basics
We allow the autopilot to continue to control our
vessel’s heading. There are only weak currents at our
present position. However, we know how difficult navigation through the Race can be and need to decide how
we will manage our onward course. We note our last
GPS position, time and heading on our paper chart.
From this point onward the chartplotter will be used to
display radar and sonar data.
Fortunately we are familiar with the area and know
that by correlating information from the radar and
depth sounder we will be able to establish our position
with the precision we will need to deal with the fog we
know lies ahead. We settle back and wonder what
caused the loss of all of those satellite guidance signals.
The light in the northern sky is the Northern Lights,
bands of glowing ions in the upper fringe of the Earth’s
atmosphere created by massive streams of incoming
energy from the sun. The solar energy that’s creating the
overhead light show is interfering with the signals from
the navigation satellite systems. Similar solar events
have knocked-out electrical power grids. Signals from
the land-based, megawatt Loran transmitters (the ones
that had been modernized just before the system was
destroyed) had provided excellent PNT (Positioning,
Navigation and Timing) information even when the sun
was screwing up the satellite signals.
