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  #1  
Old 17 Oct 2004
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compasses and magnetic inclination

Is it feasible to travel in the Sahara with a compass purchased in N. America? Do I need a compass balanced for the Equitorial zone or a global needle? Any help would be greatly appreciated. Thanks.
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  #2  
Old 14 Nov 2004
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The compass has to be balanced for the Sahara area and that varies greatly from one manufacturer to the other. However, I am sure you can get one from the US as I got one as a gift sometime ago. Contact the manufacturer directly to find out, some retail outlets people will have no idea what you are talking about.

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  #3  
Old 15 Nov 2004
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As I recall, (it's been a while!) what you need to do is set the declination - or variance from true north to magentic north. Declination maps usually come with good compasses, all you have to do is look where you are on the map, and there will be what looks like altitude lines on a topo map - the lines correspond to degrees, + or - from true north.


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  #4  
Old 17 Nov 2004
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Hi Wannago, just type in "magnetic variation map" into a search engine (I used Yahoo) and take your pick of easy to follow sites. Remember, man is never lost, only temporarily unsure of his position. Mike.
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  #5  
Old 29 Dec 2004
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AB is right, balance only matters for N or S hemisphere (or to be precise, a few bands in those hemispheres). North Am will be fine and point to the same place as any other compass. Only a south hemi compass might 'drag its needle' on a shallow bodied compass. A good compass (not mine I just noticed) is stamped with its designated declination zone (NN, NNS or something like that).
This balance, or 'declination' ('incline' of needle), is often confused with/described as 'deviation' which is what Grant is refering to (and how its described elsewhere - even on my cheapo compass body) and can vary greatly as you near the mag pole in north Canada. Between the true North Pole and the mag North Pole your compass will point south!

Chris S
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  #6  
Old 29 Dec 2004
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From Sailing days as I recall the nimonic??? was.
Cadburys Dairy Milk Very Tasty ( compass deviation magnetic Variation True ) or True Virgins Make Dull Company ( true Variation Magnetic Deviation Compass ). A compass on a boat has a deviation card this is split into 360 degrees and gives the error from magnetic that the ships compass displays the boats compass is swung by inserting metal around the compass to try to minimise the error( with all the metal etc on a boat the compass needle is affected this shouldnt happen if you ensure your compass is far from ferrous objects) A good map or chart should have the variation printed on and the amount by which it increases or decreases each year you can calculate the variation for yourself. Having said all that if you can ride a compass bearing closer than three degrees I will be amazed!!!
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  #7  
Old 7 Jan 2005
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Folks,

A compass is a compass. They are not made for a particular part of the world. They ALL point to the magnetic North. You must make a calculation depending on where you are in the world to find true North from there. Look on your map to find the local deviation from true to magnetic and go from there. Some other fancy compasses may do this automatically, but they are really just looking at a map they have programed into them.

If you are planning to attach one to your bike make sure you get one that is made for automotive use. These compasses will allow you to make corrections based on the metal and magnetic activity caused by your "running" vehicle.

john
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  #8  
Old 7 Jan 2005
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Quote:
Originally posted by htdb33:
A compass is a compass. They are not made for a particular part of the world. They ALL point to the magnetic North.
With all due respect John, that's not correct. Good compasses are made for a specific parts of the world, especially those used in sighting and map reading as apposed to regular vehicle and lesser compasses.

As you said all compasses point to the north pole, but keep in mind that Earth is almost a sphere. Using a compass in the northern hemisphere isn't really a problem, the compass needle will just point north. But in the southern hemisphere the compass needle will still point north but through the ground due to Earth's curvature, so the needle will tip downwards and drag on the base plate of the compass if you hold it flat or use it on a map. A compass used in the southern hemisphere is adjusted so that it doesn't drag.

I believe that that's what Wanngo (the original poster of this thread) was asking about but we got sidetracked along the way and talked about magnetic variation.

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  #9  
Old 10 Jan 2005
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I must continue to disagree as my own experience shows that the same compass works fine no matter where in the world you take it. This was a quality lensatic compass issued by the US military. My unit had a mission involving world wide deployments. We were issued a single compass and it worked the same where ever we took it. I would also like to note that the $15 Silva I carried as a spare worked just as well.

Actually I need to correct myself, a compass does not point at the North Pole but aligns itself with the Earth's magnitic waves. So you could just as easily say a compass points South. In neither case however does the needle point "directly" at the physical point that is currently a magnetic pole. If this were the case, no compass made for the North or South hemisphere would work on the equator since a straight line would point down through the ground at one's feet.

I have personally used the same compass for cross country navigation in Montana as I used in Kenya, just south of the equator. There was no degradation in accuracy. I alway got where I was going.

I did a bit of Internet searching before I answered this post. I found both positions stated from what I would assume were respected scientific websites. However the only place I found anyone with specific personal experience related to the subject agreed with my position.

Link to review

Respectfully,

John

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NOTE: link shortened by Grant to keep from breaking the page. (see the link to the left - visible whenever you post or reply to a topic "*UBB Code is on")

[This message has been edited by Grant Johnson (edited 10 January 2005).]
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  #10  
Old 10 Jan 2005
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Quote:
Originally posted by htdb33:
I found both positions stated from what I would assume were respected scientific websites.
Could you pass on those links as well? I'm interested in reading more about this.

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Coordinates Converter – Lat/Long <-> UTM Conversion Tool.
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  #11  
Old 11 Jan 2005
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Wont work

http://www.ngdc.noaa.gov/seg/geomag/faqgeom.shtml#q5c

http://www.princeton.edu/~oa/manual/mapcompass2.shtml


Will work

http://www.newton.dep.anl.gov/webpag...ral/gen003.htm

Very long dissertation on a Mariners compass. No mention of the North South controversy

http://29.1911encyclopedia.org/C/CO/COMPASS.htm

Interesting section concerning compass "dip"

http://home.tiscali.be/comicstrip/Ma...%20Compass.htm
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  #12  
Old 14 Jan 2005
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Guys, You are discussing 'Needle Tip' here and nothing to do with the direction the compass points Tip is due to the compass needle following the Earths Flux lines as they 'drop' back to the Poles.

'Needle Tip' only occurs as you approch the Magnetic North and South poles within the Arctic/Antarctic zones - and with a less well made compass you can get needle lock, where a compass placed on a flat surface has its needle touching the bottom of the casing, and so produces an innacurate reading - as it is unable to turn - quite easy to miss in arctic conditions.
That is why compasses marked 'Global' are used for these environments they are tuned to resist tip and sometimes have a deeper casing - these Compass are not neccesarily required for the RTW use, However not all Compass' are the same.

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  #13  
Old 24 Jan 2005
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Hello,
about your compass: I can recommend the Recta DP65. That type of compass you can use all over the wolrd without changing the cell. You can also ask for a "Isogonen"-map. That shows the degree of variation of the magnetic to the geagraphic north pole at a certain point on the world. Have a look on: www.recta.ch

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  #14  
Old 4 Feb 2005
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I´m a sailor, with International License, I sailed around the word in both hemisferes.

1) The magnetic fiel is a sphera, like the planet. Only close to the poles the magnetic forces have some angle with the planet surface.

2) For road use the magnetic declination and the geographic north have not relevance. You are on the road or not.

3) Marketing people probably sell compass for north and south compass, but I sailed around the world with the same compass without problems.

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