Variation question for chart navigators - Page 2 - SailNet Community
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post #11 of 16 Old 03-15-2014
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Re: Variation question for chart navigators

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And how many folks read the title block?
---
Friend of mine was once given some charts to use on a trip in the Med. His sextant sights were consistently way off. Drove him crazy until he noticed that he had been given old French charts. They used Paris instead of Greenwich as the prime meridian.
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post #12 of 16 Old 03-15-2014
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Re: Variation question for chart navigators

Interesting chart showing change over a few hundred years:
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post #13 of 16 Old 03-15-2014
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Re: Variation question for chart navigators

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So if I fail to account for this, I could be off by a factor of 1/26,000th?

Very scary indeed. I'm convinced ;-)
NOOOOO! You will be off by 50.2 arc seconds!! An arc second is 1/3600th of a degree. Fifty of them would be 1/72 of a degree. You had best go back and re-plot all your trips over the past five years to make sure you didn't hit anything. Sharpen your pencil first.

What's scarier is the the map that Seaduction posted. Instead of the steady change of variation posted on our charts, it actually... varies! The Government is lying to us!! You could be blithely (and automatically) adjusting for the variation based on x minutes/year, when the actual variation could be going the other way. What a huge mistake!

Kudos to Seaduction for blowing the whistle on this Government-sponsored deception that is obviously causing all the groundings and collisions since charts were first issued by them. Maybe that's why they've stopped printing charts - they don't want to be sued?
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post #14 of 16 Old 03-15-2014
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Re: Variation question for chart navigators

If you think magnetic variation is dumbed down for us poor citizens, just read about the earth's climate:
What Thawed the Last Ice Age? - Scientific American
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post #15 of 16 Old 03-15-2014
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Re: Variation question for chart navigators

Paulk--Need to go on the defensive. I thought I was clear that what I enjoy doing needn't work for you. I think it's fine that we each approach navigation with his own level of competence and native ability.
And keeping close to home certainly justifies shortcuts.
Totally unrelated question--do you fly a pirate flag?
John V.
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post #16 of 16 Old 05-21-2014
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Re: Variation question for chart navigators

This is card (half a letter sized sheet of paper) that I made some time back to help me with the TVMDC calcs - has the formulas on the sheet as well as time distance formulas worked out - no putting your thumb on "60 D street" (but the circle is there also) - some constants - make out of heavy cover stock of a bright color so they don't get lost - I have given well over 100 of these out over the last few years.

Good luck with your class.

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