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Jared,

The datum shit that Stacy gave I'm almost sure was in meters or 4950 feet or
less than 1 min of arc. I think what I said was that it was relying solely
on GPS that caused the problem, not that GPS was in error.

My memory tells me that the investigating board found the ship's failure to
be relying on GPS, and not using bearings on terrestrial landmarks to prove
their position. The land marks should have shifted with the datum. Also they
should have been following their soundings more carefully so as always it is
a combination of things. In any case it was the bridge, that was held at
fault. They also may have had forward and side seeking sonar.

Joel


----- Original Message -----
From: "Jared Sherman" 
To: 
Sent: Sunday, January 25, 2004 5:26 PM
Subject: Re: USS LAMOURE COUNTY


> Joel-
>   > GPS only on Chilean charts that used a local datum without taking into
> > account the datum shift.>
>
>  That's the bottom line. This was not a GPS error, this was a navigational
DATUM error ("pilot error" as the FAA calls it) caused by using *any* means
of determining position, and then incorrectly applying it to local charting.
If they had used a sextant, they would have still run aground because they
still would have been using the wrong charts (wrong chart datum) to go with
their position.
>
>  Apparently the GPS reliably did what it was supposed to do, as it was
supposed to do. And the navigator did the unforgiveable, entering shoal
waters after incorrectly charting his position.
>
>  By the way..."USS" would be a US merchant steam ship, as I understand it.
"USN" would be a US Naval vessel. A similar small mistake is all it takes to
get the datum wrong, regardless of the method for obtaining position fixes.
>
> Well, unless you're using rods and chains stretched from the beach.
Then we can still miscount the chains.
----- Original Message -----
From: "Jared Sherman" 
To: 
Sent: Sunday, January 25, 2004 5:26 PM
Subject: Re: USS LAMOURE COUNTY


> Joel-
>   > GPS only on Chilean charts that used a local datum without taking into
> > account the datum shift.>
>
>  That's the bottom line. This was not a GPS error, this was a navigational
DATUM error ("pilot error" as the FAA calls it) caused by using *any* means
of determining position, and then incorrectly applying it to local charting.
If they had used a sextant, they would have still run aground because they
still would have been using the wrong charts (wrong chart datum) to go with
their position.
>
>  Apparently the GPS reliably did what it was supposed to do, as it was
supposed to do. And the navigator did the unforgiveable, entering shoal
waters after incorrectly charting his position.
>
>  By the way..."USS" would be a US merchant steam ship, as I understand it.
"USN" would be a US Naval vessel. A similar small mistake is all it takes to
get the datum wrong, regardless of the method for obtaining position fixes.
>
> Well, unless you're using rods and chains stretched from the beach.
Then we can still miscount the chains.

   

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