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GPS-assisted groundings
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There are a couple of lessons here, but the basic one
is, GPS won't do your navigation for you. You still need to think,
you need at least two sources of data when fixing your position, and you
should never, never, never use GPS to make a precision approach
under any conditions - particularly at night! - unless
you have personally verified beforehand that it is correct.
We are personally acquainted with at least three boats that had
mishaps due to misuse of GPS or satellite navigation.
- June, 1990. Tuamotus, French Polynesia. The guy set
the waypoint of his destination but failed to draw a line on the
chart over the proposed track. If he had, he might have
noticed that the rhumb line passed directly through an atoll at
about the halfway point. He departed in the evening and about
midnight encountered the unexpected obstruction on his route.
I ran into the skipper of this vessel in Pago Pago, American Samoa,
a month or two later and got this story directly from him.
Ouch!
My friend Fred Bohme, KH6UY, was running the Pacific Seafarers
amateur radio net at the time, and he took the Mayday call. He
told me he was surprised that the guy knew what he'd hit.
Usually, boats hit reefs because they're lost.
- Summer, 1999. Glacier Bay, Alaska. Friends of ours
were using his chartplotter to thread a rather tight passage and get
by a nasty rock. When the chartplotter showed they'd passed
the rock, they throttled up and then hit the rock the chartplotter
showed they'd missed! Fortunately the damage wasn't too severe; it could have
been much worse.
- May, 2002. Marquesas, French Polynesia. A friend of
ours picked up (pirated, but that's another issue) navigation software and charts from a
questionable business in La Paz. I mentioned the shortcomings
of computer charts and GPS positioning, to no avail. He was
totally captivated by the precise-looking displays, and brushed off
my warnings.
Following a slow and uncomfortable passage from Mexico to the
Marquesas, they arrived off the harbor about 1AM on a moonless,
heavily overcast night. Instead of waiting a few hours until
daylight, they decided to carry on and enter the harbor using radar
and their new computer chart software.
When heavy squalls hit, the radar was useless but they continued
on, into a harbor they'd never seen before, crowded
with yachts (most of whom were probably not showing anchor lights), using only the GPS-interfaced computer charting package. It
wasn't long afterward that they hit the cliff some distance from the
harbor entrance and holed the boat, which immediately sank.
Fortunately this couple and their two young girls were able to get
ashore without injury. Their uninsured boat was a total loss.
Unfortunately for them, they'd failed to take note of the little
warning on the chart, stating that a major adjustment was required
for plotting GPS positions. We got the full story from these
unfortunate folks in an email we received a
month later.
We've heard countless other tales of boats hitting reefs
or being lost due to relying completely on GPS.
January, 2006: Abemama, Kiribati. Church
bells. I don't know where all the oxygen cylinders come from, but
they're found at churches almost everywhere in Oceania...
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