Lady Anne (W40) Hits Rock In Glacier Bay
First, for an excellent account of this incident, I refer all to <
http://www.sailblogs.com/member/annehays/?xjMsgID=91112 > Anne's excellent
narrative and critique of this regrettable incident. All is well and they
are hauled and preparing for a repair.
In her critique of the incident, Anne brings up points worthy of discussion.
First, she makes reference to the fact that the charted position of the rock
is wrong. It is my belief that there is only one way available to us to fix
the position of an obstacle and then, only in reference to other immovable
charted feature - that's with radar. Insert all the necessary caveats. If
you have the right software and GPS, you can locate a rock with absolute
accuracy by having the software throw out all the "outliers" using the
underlying GPS criteria and using the locus of the position over time.
However, that is for the modern surveyor.
The underlying survey is probably very old and likely inaccurate by today's
standards - even with an adjusted datum. So you cannot really say the rock
is 138 feet from where it is supposed to be. Only a NOAA survey vessel or a
CG buoy tender likely has the right equipment and software for absolute
accuracy. The school solution is to give charted obstacles and hazards a
wide berth. Anne's point about Nobletec's plot line overwriting and
obscuring the hazard is a good one, but would not obtain if the navigator
had chosen an offset from the hazard greater than the known extreme error of
GPS. Had there been a hazard marker, their radar would have helped them
avoid the rock.
In sum, Willard's are very tough boats, it takes several things to conspire
to create a tragedy, and neither charts nor GPS are absolutely accurate for
practical purposes. Oh, and the USCG is wonderful.
In case I'm coming across as a know-it-all; I wish to point out that with
Selective Availability (SA) turned to zero in the first Gulf War, I blasted
between ledges at 7.5 knots under sail on the Western edge of Nantucket
Sound. Had the ledge locations been off from their position on the charts, I
would have gotten to test the strength of my hull too.
Ron Rogers
Ron makes the point that "It is my belief that there is only one way
available to us to fix
the position of an obstacle and then, only in reference to other immovable
charted feature - that's with radar."
I respectfully suggest that doing so would place the radar equipped vessel
directly on top of the rock.
Otherwise you need to play with offsets. A technique that introduces a
whole new set of problems.
From the photos, this rock looks to be close to other visible shorelines.
That means more traditional methods are available to accurate positioning,
such as horizontal bearings to other charted objects. As to whether these
other objects are also misplaced due to datum conversion problems is
another issue. These can be done from a dinghy or small craft able to float
over the rock at various stages of tide.
On the subject of echart plotting. Might I suggest placing a circle
around all potential hazards before laying down a route.
The radius of these circles would be whatever margin of safety the
navigator is comfortable with. ( 500 feet -1000 feet)
Once all potential hazards have been so marked the actual course track plot
can be done. Potential danger points also include turning points in the
plot.
If for any reason a course must be plotted in between two closely spaced
danger circles, that is a good reason to note this as a location requiring
special attention by look outs and the navigator. Or it suggests DON'T GO
THERE - find another route
Admittedly I have not played with all the various chart plotter programs
presently available; but the ones I worked with before had the ability to
mark a point with a circle.
regards
Arild
----- Original Message -----
From: "Ron Rogers" rcrogers6@kennett.net
To: WillardBoatOwners@yahoogroups.com
Cc: passagemaking-under-power@lists.samurai.com
Sent: Monday, June 08, 2009 12:57 PM
Subject: [PUP] Lady Anne (W40) Hits Rock In Glacier Bay
First, for an excellent account of this incident, I refer all to <
http://www.sailblogs.com/member/annehays/?xjMsgID=91112 > Anne's excellent
narrative and critique of this regrettable incident. All is well and they
are hauled and preparing for a repair.
In her critique of the incident, Anne brings up points worthy of
discussion.
First, she makes reference to the fact that the charted position of the
rock
is wrong. It is my belief that there is only one way available to us to
fix
the position of an obstacle and then, only in reference to other immovable
charted feature - that's with radar. Insert all the necessary caveats. If
you have the right software and GPS, you can locate a rock with absolute
accuracy by having the software throw out all the "outliers" using the
underlying GPS criteria and using the locus of the position over time.
However, that is for the modern surveyor.
The underlying survey is probably very old and likely inaccurate by
today's
standards - even with an adjusted datum. So you cannot really say the rock
is 138 feet from where it is supposed to be. Only a NOAA survey vessel or
a
CG buoy tender likely has the right equipment and software for absolute
accuracy. The school solution is to give charted obstacles and hazards a
wide berth. Anne's point about Nobletec's plot line overwriting and
obscuring the hazard is a good one, but would not obtain if the navigator
had chosen an offset from the hazard greater than the known extreme error
of
GPS. Had there been a hazard marker, their radar would have helped them
avoid the rock.
In sum, Willard's are very tough boats, it takes several things to
conspire
to create a tragedy, and neither charts nor GPS are absolutely accurate
for
practical purposes. Oh, and the USCG is wonderful.
In case I'm coming across as a know-it-all; I wish to point out that with
Selective Availability (SA) turned to zero in the first Gulf War, I
blasted
between ledges at 7.5 knots under sail on the Western edge of Nantucket
Sound. Had the ledge locations been off from their position on the charts,
I
would have gotten to test the strength of my hull too.
Ron Rogers
http://lists.samurai.com/mailman/listinfo/passagemaking-under-power
To unsubscribe send email to
passagemaking-under-power-request@lists.samurai.com with the word
UNSUBSCRIBE and nothing else in the subject or body of the message.
Passagemaking Under Power and PUP are trademarks of Water World
Productions, formerly known as Trawler World Productions.
__________ Information from ESET NOD32 Antivirus, version of virus
signature database 4139 (20090608) __________
The message was checked by ESET NOD32 Antivirus.
Jeff Siegel's Active Captain and charts shows the position the boat's
GPS shows where it struck and the location where the rock is as almost
indistinguishable. The chart scale is 80K to one.
In other words, 2 waypoints; one each at the rock and the boats position
overlap such that at 100 percent zoom you can barely tell them to be two
separate waypoints.
The difference is about 100 feet north and 30 feet west.
The only way to get the dots to separate is to over zoom.
The scale of the chart is simply to small to support such chart
plotting, whether using or not using the GPS.
It would take a chart scale of about 10K or less to support such close
proximity approach and using the GPS.
In other words, the chart is not of such detail to be used to fix the
rocks position within about 100 feet. And even though we now have the
exact position accurate to within??? 10 feet or so, the chart won't
support plotting it to that accuracy.
Mike
Capt. Mike Maurice
Tigard, Oregon (Near Portland).
Correction, it's about 10 feet west, not 30.
Mike
Capt. Mike Maurice
Tigard, Oregon (Near Portland).
Good point Mike.
ECharts are derived from paper charts which are created to be used at a
certain scale.
Unfortunately with eCharts most users forget this basic element of chart
creation. The ability to zoom in simply aggrevates the situation.
Ther are rules governing how much detail to include for a given scale.
All hydrographic offices follow similar rules in guiding them in creating
a chart for a given area.
When we went out to do revisory surveys the hydrographer in Charge told
us what scale we shoudl be working to . Our field note work was always done
to four times the detail level as what th efinished weork woudl be
displayed at. So a finished chart at 40,000 : 1 woudl be surveyed to a
10,000 : 1 scale. That told us when to include or ignore some details.
If we didn't we would be cluttering up our field work notes needlessly
and create a nightmare for the cartographer in the office to sort
through.
Arild
----- Original Message -----
From: "Mike Maurice" mikem@yachtsdelivered.com
To: "PUP" passagemaking-under-power@lists.samurai.com
Sent: Monday, June 08, 2009 2:06 PM
Subject: Re: [PUP] Lady Anne (W40) Hits Rock In Glacier Bay
Jeff Siegel's Active Captain and charts shows the position the boat's GPS
shows where it struck and the location where the rock is as almost
indistinguishable. The chart scale is 80K to one.
In other words, 2 waypoints; one each at the rock and the boats position
overlap such that at 100 percent zoom you can barely tell them to be two
separate waypoints.
The difference is about 100 feet north and 30 feet west.
The only way to get the dots to separate is to over zoom.
The scale of the chart is simply to small to support such chart plotting,
whether using or not using the GPS.
It would take a chart scale of about 10K or less to support such close
proximity approach and using the GPS.
In other words, the chart is not of such detail to be used to fix the
rocks position within about 100 feet. And even though we now have the
exact position accurate to within??? 10 feet or so, the chart won't
support plotting it to that accuracy.
Mike
Capt. Mike Maurice
Tigard, Oregon (Near Portland).
http://lists.samurai.com/mailman/listinfo/passagemaking-under-power
To unsubscribe send email to
passagemaking-under-power-request@lists.samurai.com with the word
UNSUBSCRIBE and nothing else in the subject or body of the message.
Passagemaking Under Power and PUP are trademarks of Water World
Productions, formerly known as Trawler World Productions.
__________ Information from ESET NOD32 Antivirus, version of virus
signature database 4139 (20090608) __________
The message was checked by ESET NOD32 Antivirus.
Actually that's just what I meant in the context of settling a dispute. On a
calm day, drift up on it and take radar range and bearings. You do this in a
Willard, not a SeaRay. {;*)) Reading the account you will note the real
damage was done when the 33,000 pound (+) vessel fell from its perch on the
rock onto more of the rock.
Ron
Ron
-----Original Message-----
From: 2elnav@netbistro.
Ron makes the point that "It is my belief that there is only one way
available to us to fix
the position of an obstacle and then, only in reference to other immovable
charted feature - that's with radar."
I respectfully suggest that doing so would place the radar equipped vessel
directly on top of the rock.
Good morning! Over many years and thousands of miles passaging I have
learned there is no "Best Method" to avoid "Uncharted rocks"! I trust no
charts completely after a few interesting entrances to anchorages. The idea
to circle the potential hazards on the chart is a good one but in addition I
would listen to my gut. When your gut starts to flutter back off and take
another look. Needless to say in most cases when I did bump my way to a safe
anchorage it was due to my own inattentiveness or being distracted. This is
especially true after many days of standing watches or long days. On these
occasions take the time to really asses the situation and stay alert! God
Bless - Ross 10&2
On Mon, Jun 8, 2009 at 7:09 PM, Ron Rogers rcrogers6@kennett.net wrote:
Actually that's just what I meant in the context of settling a dispute. On
a
calm day, drift up on it and take radar range and bearings. You do this in
a
Willard, not a SeaRay. {;*)) Reading the account you will note the real
damage was done when the 33,000 pound (+) vessel fell from its perch on the
rock onto more of the rock.
Ron
Ron
-----Original Message-----
From: 2elnav@netbistro.
Ron makes the point that "It is my belief that there is only one way
available to us to fix
the position of an obstacle and then, only in reference to other immovable
charted feature - that's with radar."
I respectfully suggest that doing so would place the radar equipped vessel
directly on top of the rock.
http://lists.samurai.com/mailman/listinfo/passagemaking-under-power
To unsubscribe send email to
passagemaking-under-power-request@lists.samurai.com with the word
UNSUBSCRIBE and nothing else in the subject or body of the message.
Passagemaking Under Power and PUP are trademarks of Water World
Productions, formerly known as Trawler World Productions.
Just to be clear; the rock under discussion was on the chart. Arild and I
were discussing how to deal with charts based upon old surveys and before
the advent of LORAN and GPS. The datum used then was also different. A good
chart in the Caribbean based upon a British Navy survey in the 1800's was
only 100 yards off. That's darned good so long as you don't set your
autopilot based upon that chart's position of an opening in a reef! Although
there are now better privately created charts, all you can expect from an
electronic chart is the correct datum for GPS use; unless of course you
learn through experience otherwise. You can also and should mark up your
paper charts with both public and your own corrections.
The further you are from commercial shipping lanes, the less likely a recent
survey has been performed. Local sources suggest the last Glacier Bay
surveys are 50 to 70 years old. It is unlikely that the rock has moved,
although you are betting that: they sounded the full dimension of the
obstruction, their survey was accurate, and that the datum has since been
converted to a GPS compatible datum recognized by your chartplotter or
software.
Not too long ago on www.panbo.com he recounted how Garmin was out surveying
a local lake for a series of fishing charts. They were in whalers loaded
down with gear and going back and forth across the lake.
There is one thing that I do that you may wish to do from the comfort of
your homes. I do it in Coastal Explorer and also use Google Earth. You can
compare airborne and satellite imagery to your paper and electronic charts.
In almost every case, the often undated images will be newer than the chart.
I use the imagery for shoreline erosion, shifting sands (much less reliable)
and the location of rocks. You are only forming impressions and not absolute
facts. But if you want to know what points of land are suspect and where a
body of water is shoaling, these methods work. Unless removed by man or a
dramatic natural event, rocks are rocks.
Ron Rogers
What is interesting is that Ken Williams from "Sans Souci" was at the
collision site.
http://www.kensblog.com/aspx/blob2/blobpage.aspx?msgid=463430&beid=28555
Scroll down about 1/2 way.
John Ford
PUP Admin