Always trust your compass? Right? Wrong!

D

David_S

New member
Was tramping up a river bed with my son in a remote part of New Zealand last week when we came across a lot of rusty looking rocks. Speculating that they might contain iron I tested one with my compass - not a flicker. But then I thought "Crud! No way is North that way. Must be a big anomaly around here."

So my son pulled out his identical compass and this is what we found



Seems as if the polarity of mine had been reversed. Apparently this can happen if a compass is exposed to a strong magnetic field over a period of time, but I can't think where this could have happened. I keep it in the top pocket of my pack which it sometimes shares with GPS, binos, camera, rangefinder and topo map.

Thought I would mention it on the forum as something to be aware of as it could really throw you if relying on a compass in thick bush or in fog such as below.


I think I will make it a practice on future trips to always check my compass when I set out. In practice we don't use compasses a lot as navigation is pretty simple in this mountainous terrain though finding a safe route can be problematic.

I believe you can reset the polarity by stroking with a strong magnet. Anyone tried this?

David
 
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I have read about this problem but have never experienced it. I now carry a second compass (different brand but similar design) and I keep them as separated as possible. I have not had to reset polarity, but have read that it works. I like Silva, Suunto and Brunton.

Also: I would love to hunt in New Zealand but doubt if I will ever be able to afford it. I spent a week in Sidney, Australia about 43 years ago (a brief "vacation" during my tour of duty in Vietnam.)
 
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Sound like the GPS might be a problem...

never had a "Silva" go bad like that.

I have observed other hunter come up to me asking to confirm North and I'll ask why and observe that they are holding their compass right by the firearm.

leave out iver night on wood post and see if it reverses.
 
I believe you can reset the polarity by stroking with a strong magnet. Anyone tried this?
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Never done that stroking thing. But if you think it can be done. Why not. After all your compass in its present condition you'd be better off carrying a sextant.

Since your compass only had a 1 year warranty. I would just pitch it and buy another. I've used one of their Fish Eye compass's for a few years now without any problems. But I indeed have seen a compass or two over the years get bounced off the side of trees and left where they landed for future historic discovery.:mad:

S/S
 
Whats a Compass? I thought GPS obsoleted them.:D
Just kidding, I keep my Compass in my hunting pack. I keep my GPS in my pocket.;) I have a surplus Vietnam war U.S. army Compass. I think it could survive being run over by a tank.
 
If you stroke it and get it fixed, will you ever trust it again. I always carry one of those Marbles, pin on ball compasses to check my good compass
 
Apparently a known problem

Did a bit of goggling and found this in the FAQ on the Silva website

My compass no longer points North. Is this normal?

Please be aware that a reverse polarity is caused by exposing your compass to articles with iron content (something as simple as being placed next to a pair of scissors or a knife for a length of time, microwaves, high tension wires, etc.). Your compass can be repaired at no charge. Please contact us in advance for a return authorization number and shipping address. From the U.S.A, call 1-800-572-8822 between 8 am-6 pm, eastern time. From Canada, call 1-800-263-6390
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Not a great help to me in NZ so I think I will try stroking mine with a magnet.

Whats a Compass? I thought GPS obsoleted them.
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Ah! But a compass does not require batteries:)
 
I used to be an instructor on the army. Of all the training a did as well as the classes I did the instruction, the map and compass was the most testing.

The military compass isue usauly has a mirror in it. We juked and said it isso that you can see who is lost!
 
One thing that I always thought I could trust was my compass. There have been a couple of times that it came down to believing the compass or believing what every fiber of my being told me was the right direction. I always went with the compass and always got home. Now you've made me nervous.:)
 
Just guessing here, but if you keep it with your GPS, which is an electronic device, with a magnetic field, that may have done it.
 
I have the same compass a few months ago it was sitting on a shelf and I noticed it was wrong.. I thought that is weird, so I showed the wife and she pointed out it was next to a key holder that had a magnet. never knew.
 
Like LT Dan...

I was also a US Army instructor - for 4 years on active duty, plus 8 years in the Army Reserves.

As LT Dan stated, the "Map Reading & Land Navigation" courses (usually 8 hours classroom and a 4 hour practical exercise) was most challenging to teach, and most difficult for students to learn.

Other instructors frequently asked me to take over "Senior Instructor" duties for them, while they served as assistant instructor. Since my branch was Field Artillery, I was accustomed to being sure I knew where the rounds were going to land before initiating firing commands.

That said, I always used 2 compasses, AND a topo map, in conjunction with each other. In teaching students to use a compass, I included the precaution to be aware of magnetic influences, such as the presence of iron objects (rifle, pistol, trucks, railroad tracks, overhead power lines, hand grenades hanging off your web gear, etc.) The army even specified exact "standoff distances" for each object, and included several questions in the end of course test to be sure the students understood/learned that a compass needle is sensitive to magnetic distractions, some of which are not obvious.

As far as iron ore soil/rocks, underfoot, you can't standoff from such being underfoot. That's when your topo map is your best hope. "Don't leave home without it" is a good rule of thumb.

Now I must humble myself a bit.

I was hunting in thick cover in the East Texas Piney Woods, a mile or so from the nearest road, following a creek bed, and decided to walk back to the road on a straight line, using my compass. It was cold enough that I was wearing a pair of mittens over a pair of gloves. The mittens had a feature that allowed you to fold back the part that covered the fingers, thus allowing greater dexterity with the fingers. When folding back the finger covering, a magnet in the finger covering clung to another magnet on the back of the hand.

So, I uncovered my fingers to more easily manipulate the compass, and proceeded to march straight toward the road, stopping every 50 paces to hang a blaze orange piece of surveyors tape on a tree, so I could return later and set up a tree stand. After marking off about 4 such waypoints, I looked at my back trail and noted that I had formed an erratic zigzag with my markers, rather than the straight line I had expected.:confused:

First, I checked my 2 compasses against each other, and they were erratic. Then I shot a back azimuth from my location to the next marker.It was wrong, with both compasses. Finally, I carried my rifle (a possible magnetic distraction)10 yards off the trail, then went back to my last marker and measured the back azimuth with both compasses. Every azimuth I measured, both compasses, was erratic.:mad:

Searching for other magnetic distractions, I discovered the magnets in my mittens. I took the mittens off, put them with my rifle, 10 yards away, then took azimuth readings. Problem solved!:p I then went back to my first waypoint, collecting all of my markers, and proceeded to lay out a straight line to the road.

Lesson learned.:rolleyes:

The magnetic mittens stayed in the woods!:D Ten yards off the trail!
 
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Which compass?
I have a military lensatic, a watch compass and a mini compass on my watch.
And a GPS.
They might find me nose down in a field some day, but my head will be pointing toward camp.
 
Another comment

While I realize you put the two compasses within an inch or so of each other so we could see the reverse polarity, they should be separated by 5 meters when checking one against another. This is so because each needle is magnetized, and the magnetic field of one will interact with the magnetic field of the other, causing both to be inaccurate, even when the polarity is not reversed.
 
As Kraigwy said, you can find South with an analog watch or you can make a rough sundial if you have a digital. Point the hour hand at the sun and halfway between the hour hand and 12 is relative South.

When I'm out in the great outdoors I tend to depend more on maps and knowing various geographical features. If this is stream X and that is mountain Y then I should be about here.

Here In Washington, if you can see one of the big mountains general directions are a snap. If you start the day with Mt. Adams West of you, it's always going to be West.
 
I can recall a couple of such adventures.One was somewhere in the vicinity of Pagosa Springs,Colorado.I had stayed on my stand late,was traveling in the dark.Must have been magnetic iron in theground somewhere,my compass was totally confused.So was I.I got into a a bunch of little finger ridges with beaver bogs between them.I found myself on a little patch of ground surrounded by beaver pond and bog,no light,and,elk season in Colorado is never swimming weather.

A buddy helped me out of that one..he knew the country,I did not.(Yeah,I know,I did not do everything right.I did stay dry)

Another one had to do with a nice Hawken rifle I built off the Cherry Corners original blueprints taken from Mariano Medina's rifle.

The Sharon barrel was magnetic.It got tiresome setting that rifle down,walking off a ways,then going back to pick it up,but it sure confused a compass.
 
Some useful comments, thanks.

Thanks for the comments and stories, everyone. Had a few chuckles and could relate to some of the incidents.

I agree that the best navigation tool is a topo map in a waterproof bag. I use MemoryMap to print off an A4 sheet of the area I am going to and put it in a ziplock bag. I also print off a second copy which I mark up with our route and intentions and leave with my wife.

I have tested the compass with all the things I carry close to it in my pack. Nothing obviously affected it. Not surprising seeing that Rangefinders etc are mostly plastic or stainless steel which are not magnetic materials. I too suspected the GPS but the compass barely twitched with the GPS whether on or off.

Before taking the photo I did wander around with the compass a bit to see if that made a difference. But nothing. We then pulled out the other one which worked fine.

I haven't "stroked" mine yet as I want to take it along to our next volunteer SAR training session as an example. We use compasses occasionally for such things as maintaining the line of a search or taking cross bearings on the location of a missing person identified by a cry or by light.

Now you've made me nervous
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I agree with you 603Country. The main purpose of the post is to make people aware that compasses can reverse polarity and to check them before use. There is one indication that reversal may have occurred which will be apparent in the field. If you place the compass on a flat surface and the needle is tilted badly so that it is touching the card or close to it then polarity reversal may have occurred.

For those who don't know, the reason is that the Earth's magnetic lines of force are not parallel to the surface of the Earth. A compass needle tries to align itself with the lines of force so that in the northern hemisphere the north end of a compass needle will point downward and in the southern hemisphere upwards. (Google "angle of dip")

I believe compass manufacturers compensate for this with the bearing alignment so that the needle will swing freely (this is the reason why Northern hemisphere compasses don't work well in the southern hemisphere). So if your compass polarity is reversed the needle will drag indicating a reversal may have occurred. We commented on this at the time without realising the significance - in my original photo the faulty compass is the one with the white lanyard.

Does this make sense?

David
 
I have done the resetting by stroking a needle with a magnent. It does work but it is easier said than done. I had to use two magments and there is a trick to it.
 
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