[PUP] Lady Anne (W40) Hits Rock In Glacier Bay

[Ron Rogers]

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