Observations on ferrous interference on compass use

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Bushman5

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Oct 31, 2007
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finally dug up the draft i had written a while back......:p

Observations on ferrous interference on compass use:

normally my map is on my drop down panel on my HSGI chest rig, along with my SUUNTO forestry compass for easy direction plotting. There is usually a folding knife in the office admin panel of the chest rig, and a fixed blade on my belt. There is a fire kit, with ferro rod and scraper as well in one of the Admin pockets. Lots of metal around the map nav area......

.....which leads me to these observations taken over the last few months of bushwacking.

- removing the folder knife and fire steel AWAY from the front of the chest rig and into my belt kit shows a 5 degree +/- change in compass needle direction.

- removing the above items AND the fixed blade, and placing them near the small of my back, shows a 7 deg +/- change in compass needle direction.

- if wearing a pack with gear in it like a folder, stove, ferro rod etc, removing the pack and placing on ground 5 feet away shows a 3 - 5 deg +/- change in compass needle direction

- if wearing my SAS jacket with heavy YKK metal zipper, removing jacket and re-reading compass shows a 2 - 3 deg +/- change in compass needle direction.

- having an axe in the pack plus the other mentioned gear, when ditching that gear to the ground 5 feet away, shows a 10 - 12 deg +/- change in compass needle direction.


additional observations: big rocks will show a 5 - 15 deg change in compass needle direction when near them

something to think about when taking a bearing reading - are there items in your jacket, pack, chest rig, etc that MAY be affecting your bearing readings!

your milage might vary, these were my experiences. Compass was fixed on a stick driven into ground, and my footing did not change as i shuffled the ferrous items about or removed them. I simply stood there rigidly, took a reading, removed the ferrous items, and took another reading.

:cool:
 
i was always told to stay away from metal and electrical objects when taking a good reading on a compass.. the rock theory is interesting. perhaps it has iron or some other metalic type substance in it? who knows?
 
hematite or magnetite are often present in rocks. Both throw off compasses quite a bit if you on or near rocks that contain them, or soil, or sand etc....
There are portions of the Fraser Canyon in BC Canada that are completely unnavigable by compass, due to the huge concentrations of both hematite & magnetite in the soil and rocks.
 
There is an area just off-shore of Lubec, Maine that is marked on navigation charts as having unreliable compass readings. Must be a big ol' chunk of iron on or under the sea bed. If you want to see a real mess though, check out a declination chart for Greenland.
 
Compass readings are also unreliable in the vicinity of Black Kaweah in Sequoia NP.
HamiltonLake2008515.jpg
 
Good information. I have always wondered if a knife, say a neck knife that is magnetized wouldn't royally screw-up a compass that is hanging from a lanyard.
 
Bushman5 said:
hematite or magnetite are often present in rocks. Both throw off compasses quite a bit if you on or near rocks that contain them, or soil, or sand etc....
There are portions of the Fraser Canyon in BC Canada that are completely unnavigable by compass, due to the huge concentrations of both hematite & magnetite in the soil and rocks.
Click to expand...

Yep, saw this in the Canadian Arctic. Lots of places the compass needle just swings wildly. Magnetite is present in large quantities and can really screw up compass navigation.
 
Does the presence of ferrous junk have the potential to permanently alter the compass' reading? I had one that, no matter what, read 180 off...:rolleyes:
 
Around here, there is a lot of iron in the ground which can throw off compass readings. In fact, a surveyor discovered the first ore body in Upper Michigan in 1849, because his compass went crazy. That was just a few miles from here.
 
dougo83 said:
Does the presence of ferrous junk have the potential to permanently alter the compass' reading? I had one that, no matter what, read 180 off...:rolleyes:
Click to expand...

it shouldn't. The compass would just align with the whatever is magnetic. Theres no way to mis align the polarity. well unless the compass gets electromagnetised, heated past its currie point, or smashed quite abruptly.
 
Munky88 said:
well unless the compass gets electromagnetised,
Click to expand...
Some years back I had a Timex watch with a button compass on the band. I do some arc welding in my line of work, and the magnetic fields created by the arc wound up ruining the compass. In a slightly different vein, my wife used to operate a spot welder in the factory we worked in, and the magnetic field would affect her battery operated analog watch. Magnetism is a weird thing!
 
I like a magnetic compass first learned to navigate and read a map with one , however back up is always wise and a gps with fresh batteries is a blessing , or using the stars or the sun to confirm the compass or even using a topo map and use terrain features to orintate your self.
 
I have to keep the compasses and magnetic stuff away from me beacuase there is iron in my words.......
 
Unless you plan on hiking nude I would suggest you get a new compass.
I don't know what model compass you have but there are alot of bad ones being produced and sold by what used to be good companies.
As an example The current Silva Ranger is getting terrible reviews on the REI web site. In the past the Ranger was concidered a first class product.
The current Silva Rangers are made in China, the older ones were made in Finland. I heard that the Finnish made rangers are now sold under the Brunton label.
For all I know Silva may not even be a in business anymore It may now just be a name that some corp. bought the rights to. Like Schrade, Smith & wesson and Winchester knives.
 
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