Compass trouble

[Tony Anders]

When I was out yesterday , I was trying to get bearing on my compass and it didn't appear to be giving me a true reading. I tried my GPS and it appeared to have the same type of problem. Does anyone know if railroad tracks can interferre with compass and GPS system. I have used my Sylva compass alot backpacking and hiking with no known problems.

Anyone have any idea what might have been wrong yesterday.

This might have been some reasons why we couldn't locate our cave we was looking for.

Again thanks in advance for everyones help.

Tony

[Azurerana]

Railroad tracks can, if you are too close to them. Compasses can and are swayed by refined steel (try setting it on the hood of your car), rich buried iron ore deposits, lightning, static accumulations, electrical wires with current (electromagnets). I was lost once for hours as a 10 year old Girl Scout, following a leader who was following a compass which was pointing at her metal watch. If there were trains on the track, you've got the additional problem of the diesel electric engines...even small LED lights with their electronics can mess up compasses by a degree or two.

As for GPS-- what was the error with the GPS? As an electronic device, it could be messed up by electrical fields, but I'd need to know it's malfunction to comment further.

[madratdan]

What model GPS are you using? My Garman Vista GPS compass can be set to run electronically or magnetically and yes, railroad tracks do point North. So does a herd of cows with cow magnets in them. They tend to swing compasses too.

[jonsdigs]

The way we handled minor magnetic deviations when I was a geologist was to back-sight all our readings. To do this you always sight back to the station you just shot and compare readings. A way to deal with minor discrepancies is to average the two readings. If one reading is way off and shooting over doesn't change it you might want to throw out the readings from that particular station altogether and use the readings from either side of it. Up in the Iron Range of Minnesota, everything had to be shot from known references by measure of the angles with a transit theodolite as compasses were useless.

GPS is not based on the Earth's magnetic field and so should not be affected as compasses are affected.

[Tony Anders]

Thanks for all the input. I am using a Garmin GPS+II and it would log into to the sats and give us the co-ordinates, but that when I clicked to the compass screen it would move when I was turning or anything. I really don't know what the deal was that day, that hadn't ever happedned before.

There was, however, a train engine setting on the tracks there where they havd been doing some work on the track system.

Thanks for everyones input again.

[Brian Roebuck]

Train Engines (Locomotives) are driven by electric motors that are pwoered by the big diesel engines in them. I suppose if it were running it could have caused some local magnetic disturbance to your compass but not to a GPS. Perhaps your GPS had picked up different sattelites, was using the wrong settings, or just malfunctioned somehow.

I'm stumped?

[Azurerana]

Tony indicated he had turned his GPS to the compass mode. It sounds like the satellites were originally OK, but once he put it into compass mode, the compass part was afffected by whatever field was messing up the Silva. I don't have a compass in my GPS, so I don't know if there is some electronics connecting the two. I would think the wayfinder mode on the GPS would be fine, as long as you just kept it in GPS mode.

Another thing to watch for: two compasses will point at each other. Maybe turning off the GPS while taking a compass reading, and vice versa.
The answer to the compass problem is to have a topo map with you and check the topography against what are seeing. Also, moving a couple hundred feet from anything obviously electrical or magnetic or metal might do the trick with the compass. (Won't work with the iron deposit problem-- that requires a geological knowledge of the area where you are. )

[madratdan]

jonsdigs said:

GPS is not based on the Earth's magnetic field and so should not be affected as compasses are affected.

Jon,
On my GPS unit I can toggle between GPS and magnetic mode for compass use. This feature lets me use the built in compass to navagate when I cannot pick up a signal, such as deep canyons and dense forest. I believe the model Tony owns might have the same feature built in.

Tony,
Check the owners manual and see if this might be the case. If so, that might have been your problem.