Topic: Magnetic variation in the Mournes (Read 18934 times)

Mourneman · « **on:** July 25, 2012 »

Doing some navigation planning last night & discovered that the Magnetic variation in the the Mourne's is almost eight degree's

& i've always only added two degree's,here's the website explaining it - http://www.ufrc-online.co.uk/advice/grid-references/ also found this very basic but useful youtube video on compass use -

twentyclicks · « **Reply #1 on:** July 25, 2012 »

I believe it's only 4 degrees. Checking some sources here as it's something to get right!

twentyclicks · « **Reply #2 on:** July 25, 2012 »

Well, my 2009 map shows 6degrees 12mins W decreasing by 10mins E each year. That would put it approx 5degrees 40mins W now, although when I was in the Alps our guide told us it was increasing in rate.

This website puts the Mournes at 4degrees 10mins W

while this website puts the Mournes at 4degrees 05mins W of True North. It also notes that convergence on OS mapping puts the

Grid North at this location to 3degrees 17mins W of True North, so...

Magnetic North is only 48mins (just under 1degree) W of Grid North...

Mag N -- Grid N ------------- True N
4 3 0

I'm not sure what that means in application? Taking a magnetic reading and applying it to grid (map) there is only 1 degree difference. The grid discrepancy from true north is probably not an issue over the short distances you will be sighting as the general area will fall under the same discrepancy, although using stars to navigate (ie. Pole star @ true north) may be further off on the map (but unless you are using theodelites or something likely less than the margin of error anyway)! More of an issue if flying or perhaps sailing!

Only way to know is to say, go to the tower on Commedagh on a clear day and take super-accurate sightings of the towers on Donard and Meelmore and see for yourself how much it is out.

Think I'll cut my losses and just add 1 or 2 degrees and be mindful of features, or aim off.

twentyclicks · « **Reply #3 on:** July 25, 2012 »

me again... if you click the heading on that second link it goes into a whole world of explanations with links to downloadable reference leaflets, etc.

John, you've opened pandora's box now

whoRya · « **Reply #4 on:** July 25, 2012 »

Sooo...I'll ask the question everyone wants to know. Do I turn the dial on my compass clockwise to add the variation?

Mourneman · « **Reply #5 on:** July 25, 2012 »

Good one,it's anti-clock wise

A bearing of 36 SW degree's become 44SW degree's by turing the dial anti-clock wish adding the 8 degrees,correct me if i'am wrong

twentyclicks · « **Reply #6 on:** July 25, 2012 »

Mourneman is right... we need to 'add' the variance in the Mournes (however much that is!)

Note: even in other parts of the UK this will be different. Some easterly places may have negative variance!
If in doubt, it's marked on every map, so if it's reasonably current you shouldn't be too far out.

Pudd · « **Reply #7 on:** July 25, 2012 »

Quote from: twentyclicks on July 25, 2012

Note: even in other parts of the UK this will be different. Some easterly places may have negative variance!
If in doubt, it's marked on every map, so if it's reasonably current you shouldn't be too far out.

Correct. Flip the Mourne map over for the Castlewellan and further north side and you will see that there is a difference in variation between such a short distance.

I would personally recommend Mils, rather than degrees, I've been told, and do believe myself that it is more accurate.

Mourneman · « **Reply #8 on:** July 26, 2012 »

Doing some navigation in the mournes today,i'll put this into practise

Mourneman · « **Reply #9 on:** July 26, 2012 »

Spent well over an hour sitting on slieve loughshannon today working on Map orientation,contour's,feature finding, 7 off course " Magenetic variation " ,which after many

attempts i found that i needed to add 5 degree's,i firstly used my position on loughshannon's summit & was getting a bearing to Carn mountain.We tryed this on several peak's doan,ben crom,binnian all with the same result , 5 degree's.Before going today i called a friend who tutors for Mountaineering Ireland in Night navigation to discuss what his finding were,basically it can range from 4-6 degree's depending on where you are,sames strange to me as the Mourne's are such a small range?

IMG_1618 by peterperdoo, on Flickr

IMG_1610 by peterperdoo, on Flickr

IMG_1622 by peterperdoo, on Flickr

twentyclicks · « **Reply #10 on:** July 26, 2012 »

Very interesting! Cheers for experimenting and updating us.

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Author Topic: Magnetic variation in the Mournes (Read 18934 times)

Mourneman

Magnetic variation in the Mournes

twentyclicks

Re: Magnetic variation in the Mournes

twentyclicks

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twentyclicks

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whoRya

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Mourneman

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twentyclicks

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Pudd

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Mourneman

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Mourneman

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twentyclicks

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