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Old 27-07-2012, 00:51   #46
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Re: Compass Heading - True vs Magnetic

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Originally Posted by belizesailor View Post
Hey this is cool (and relevant). An animated isogonic chart showing change in variation (declination) over time.

File:Earth Magnetic Field Declination from 1590 to 1990.gif - Wikipedia, the free encyclopedia

Now i wonder if we could time lapse that to the low and high pressure zones, to find any correlation, then could we time lapse that to La Nina, and El Nino. BC I already know that the Jet Stream is in correlation.

Out of that come a real weather prediction.

Lloyd
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Old 27-07-2012, 01:16   #47
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Re: Compass Heading - True vs Magnetic

At random intervals (averaging several hundred thousand years) the Earth's field reverses (the north and south geomagnetic poles change places with each other). These reversals leave a record in rocks that allow paleomagnetists to calculate past motions of continents and ocean floors as a result of plate tectonics. The region above the ionosphere, and extending several tens of thousands of kilometers into space, is called the magnetosphere.


Does this reversal, happen in time, why yes, but how much time?



Lloyd
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Old 27-07-2012, 18:59   #48
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Re: Compass Heading - true vs magnetic

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Originally Posted by Adelie View Post
While deviation and variation do not specifically change in relation to the equator DIP does. Dip can affect the reading of a standard compass, especially a hand bearing compass when dip starts to cause the compass card to drag on the housing. In a gimballed ship's compass dip can dignificantly tilt the card confusing users.
Now we are talking.

Sailing with the same compass from UK to Aus is a great lesson of how thing work! I believe many makers sell them by the zones.

The post above on hand bearing compasses 100% in sync with the same phenomenon.

b.
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Old 27-07-2012, 19:18   #49
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Re: Compass Heading - true vs magnetic

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Originally Posted by Jim Cate View Post
...
Interestingly enough, a fellow cruiser from SF who had been in loose company with us and who had a Ritchie compass did not have much trouble from dip. I guess there is some difference in the geometry of the compass card and hence its sensitivity to dip changes between models. One of the many things they didn't tell us at the boat show!

Cheers,

Jim
Yes, you would think that if you designed enough clearance into the body of the compass then dip would only be an issue in extreme cases.
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Old 27-07-2012, 19:21   #50
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Re: Compass Heading - True vs Magnetic

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Originally Posted by FlyingCloud1937 View Post
At random intervals (averaging several hundred thousand years) the Earth's field reverses (the north and south geomagnetic poles change places with each other). These reversals leave a record in rocks that allow paleomagnetists to calculate past motions of continents and ocean floors as a result of plate tectonics. The region above the ionosphere, and extending several tens of thousands of kilometers into space, is called the magnetosphere.


Does this reversal, happen in time, why yes, but how much time?



Lloyd

That would be an exciting day to be one the water!
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Old 27-07-2012, 19:25   #51
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Re: Compass Heading - true vs magnetic

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Originally Posted by barnakiel View Post
Now we are talking.

Sailing with the same compass from UK to Aus is a great lesson of how thing work! I believe many makers sell them by the zones.

The post above on hand bearing compasses 100% in sync with the same phenomenon.

b.
I know that Silva makes hand helds for different magnetic zones, but have not seen much talk of this with marine manufacturers.

....something else interesting to research during off-season!
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Old 27-07-2012, 19:39   #52
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Re: Compass Heading - true vs magnetic

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Originally Posted by belizesailor View Post
I know that Silva makes hand helds for different magnetic zones, but have not seen much talk of this with marine manufacturers.

....something else interesting to research during off-season!
Also have friends with very expensive binoculars with built-in compasses that stopped working as they came south. Pretty disappointing!

Cheers,

Jim
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Old 27-07-2012, 19:43   #53
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Re: Compass Heading - True vs Magnetic

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Originally Posted by Randyonr3 View Post
Without using a GPS, or electronics, how do we create a compass card
for different areas of the world?
My, my, my, we have certainly drifted a bit on the thread. Must be made of the strongest thread known to man!!
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Old 27-07-2012, 20:01   #54
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Re: Compass Heading - True vs Magnetic

Yes.

There is at least one make (not sure if Silva or Ritchie, or maybe both?) that claims they can deliver a multi-zone compass.

This may be a good buy for a boat that is about to be sailed thru various zones.

b.
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Old 27-07-2012, 20:07   #55
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Re: Compass Heading - True vs Magnetic

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Originally Posted by Randyonr3 View Post
Without using a GPS, or electronics, how do we create a compass card
for different areas of the world?
This might be a very helpful link; Procedures for Magnetic Compass Adjustment its a .pdf

Success CeesH
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