01-19-2008
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Telstar 28
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Join Date: Mar 2006
Location: New England
Posts: 43,315
Rep Power: 11
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Lots of commercially and militarily unimportant areas are less that recently updated. The governments pay for most of the updating, and without commercial or military reasons to do so... they don't. You really should check the chart information of any chart you use to see how old the chart really is. Anything more than 20 years old is going to be less than stellar in accuracy.
When your measure of accuracy is limited to the tools of celestial navigation, which may well have been the case in many of the more remote areas, they are as accurate as was possible for the time... but the charts may not have any real congruence with the reality of GPS-based navigation.
That is why GPS is only one of a dozen or more tools you're supposed to be using... not the only tool. When you're doing dead reckoning and using coastal landmarks to position yourself... you will at least know where you are relative to any immediate land... which GPS can't tell you in areas like this.
The icon of your boat's position on a chartplotter has very little to do with where your boat is in reality. It is an estimated position of your boat in an interpretation of the real world as translated by various explorers and cartographers that happens to coincide with your boat's actual position in the real world some of the time. While your actual position is very accurate most of the time—your relationship to land in the real world and that of your icon to land in the GPS chart are not always going to mesh.
Using a GPS on electronic charts from the 1800s is kind of like measuring a board with a micrometer, marking with a can of spray paint and then cutting using a jackhammer—with much the same results.
Quote:
Originally Posted by mightyhorton
Around Banderas Bay (Puerto Vallarta), on the west coast of Mexico, the charts and the GPS disagree by up to a mile sometimes. Apparently the charts were drawn long ago and have never been updated. Does anybody know the story, the history, of who drew these charts and of where the mistakes crept into them?
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Sailingdog
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Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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Still—DON'T READ THAT POST AGAIN.
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