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Richard Langley has pointed us to information about the stranding of the
yacht "Nelly", at-

and Lu has made some wise comments.

It' near 40 years since I sailed those waters, but perhaps I can add a bit
of information (and quite a bit of speculation).

The coastguard were called at 5.11 pm, by which time time it would be deeply
into twilight. And in conditions of driving rain, we can guess that vis. was
poor, to say the least, when the stranding occurred, which was presumably
shortly before that callout.

That whole area is very shoal, and the tides are an important matter.. I
will guess that the 25 ft craft was making a passage along the coast from
the Crouch to the Blackwater, or vice versa. Most likely, just a short
high-tide hop between the two, for a weekend out. If you followed the
well-marked deep-water channels between the two, it would be a four-hour
passage, or so, but by cutting through between the sandbanks (which mostly
dry at low water) by the Ray Sand channel, you could expect to halve that
time. Even so, you have to keep a couple of miles from the shoreline, to
keep off Ray Sand. The shore itself is very flat, and the big landmarks (the
nuclear power station at Bradwell, in particular) being a couple of miles
back, would not be seen in that poor visibility. The Raysand channel itself
is poorly marked.

These sands are rather unstable, and knowing your exact GPS position doesn't
help a lot, unless you have recent local knowledge, because the channel
shifts. You need to watch the depth sounder all the time, and feel your way.

High water was 4.6 metres at 4.47 pm on that day, coming off springs. Low
water, at 11pm, was 1.3 m. In normal conditions, making that passage near
high water isn't at all hazardous, in a craft drawing a metre or so, as much
of the sands dry by 2 metres or less. In the conditions described, force 8
onshore, it would be another matter. I would expect there to be breakers all
over the sands, and so the underkeel clearance in the troughs would be
greatly reduced. The crew would be concentrating on hanging-on, without much
time or energy to devote to the echo-sounder.

That sand is like iron if you strike it, and having struck in those
conditions, near high water, escape would be unlikely. A prompt callout for
rescue would be the next step, which is presumably what happened.

The principal drawback of not having a working GPS was that they were unable
to provide a precise position to the rescuers, so that location and search
procedures were invoked, which worked well enough to allow them to be taken
off in time. They were lucky. I wonder how much is left of the craft. If
anything  survived, unless removed promptly, she would become neaped until
the next spring tide.

George.

contact George Huxtable, now at george@hux.me.uk
 or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
----- Original Message -----
From: "Lu Abel" 
To: 
Sent: Monday, November 03, 2008 7:03 PM
Subject: [NavList 6425] Re: News Item on Over-reliance on GPS


| Thanks, Richard!
|
| What's still not clear from the report is whether use of GPS in any way
| resulted in the boat's running aground.  On-shore gale force winds
| certainly seem like darn sloppy conditions for a 25' sailboat!   What
| the MCA report says is that "the yacht's GPS had failed and the crew
| could only make a rough estimate of their position [for rescuers]"
|
| It sounds like these folks had less than total situational awareness
| (eg, didn't know exactly where they had grounded), but that could easily
| be due to conditions other than the use of GPS -- for example, how many
| of us could keep a DR plot under the snotty conditions that beset this
| boat?   And the boat did run aground in daylight, so they ought to have
| seen how near they were getting to the shore.
|
| Again, I'm not excusing poor navigation practices if that's indeed what
| happened.   But I also have a lot of trouble with the tendency of
| "experts" to assign "GPS problems" as the reason for any on-the-water
| incident where the boat was carrying and using a GPS.   Some on this
| list are pilots and I understand pilots get very angry when a crash is
| dismissed as "pilot error" even before an investigation is completed; I
| see an analogy.
|
| Lu
|
| Richard B. Langley wrote:
| > A little bit more information from the Coast Guard:
| > 
| > -- Richard
| >
| > Quoting Lu Abel :
| >
| >
| >> It would be nice to have a little more detail on exactly what occurred
| >> other than "the GPS failed"   When did the GPS fail, was the skipper
| >> aware of the problem, and what navigation techniques were employed
after
| >> the GPS failed?
| >>
| >> Any skipper who just follows the his GPS blindly without situational
| >> awareness is dumb, dumb, dumb.   But I don't blame the GPS for that,
but
| >> over-reliance on it by humans.
| >>
| >> That's probably the dilemma:   with traditional techniques like
| >> celestial, bearings, and DR plots, the navigator had a high degree of
| >> situational awareness.   Using a chart for all this navigation work was
| >> unavoidable, giving awareness of what was around and beneath and ahead
| >> of the boat.   With GPS, sadly, the box just produces magic numbers (or
| >> magic "steer in this direction" commands).   I teach coastal piloting
| >> frequently, I do admit that GPS exists and is a useful tool, I spend
| >> time on how to get the most out of it, but then I also spend even more
| >> time on how to keep out of trouble when using it, and what to do when
| >> the screen goes blank.
| >>
| >> Lu
| >>
| >> Richard B. Langley wrote:
| >>
| >>> 
| >>>
| >>>
===============================================================================
| >>>  Richard B. Langley                            E-mail: lang@unb.ca
| >>>  Geodetic Research Laboratory                  Web:
http://www.unb.ca/GGE/
| >>>  Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506
453-5142
| >>>  University of New Brunswick                   Fax:      +1 506
453-4943
| >>>  Fredericton, N.B., Canada  E3B 5A3
| >>>      Fredericton?  Where's that?  See:
http://www.city.fredericton.nb.ca/
| >>>
===============================================================================
| >>>
| >>>
| >>>
| >>>
| >>>
| >>>
| >
| >
| >
===============================================================================
| >  Richard B. Langley                            E-mail: lang@unb.ca
| >  Geodetic Research Laboratory                  Web:
http://www.unb.ca/GGE/
| >  Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142
| >  University of New Brunswick                   Fax:      +1 506 453-4943
| >  Fredericton, N.B., Canada  E3B 5A3
| >      Fredericton?  Where's that?  See:
http://www.city.fredericton.nb.ca/
| >
===============================================================================
| >
| >
| >
| > >
| >
|
| |
|


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