Compass Deviation Issue

[MargaritaMike]

And don't forget a compass can go bad. I had one that made me think I couldn't follow a compass course anymore. It seems that on the surface before the dive it worked perfect, then when subjected to cold and pressure it would not swing properly. My buddy was on my a** about my lack of skill with a compass, until we were out of the water and it was pointing due east. When moved it was sluggish and stopped where it wanted. After a half hour or so during the SI, it worked perfect again.

Needless to say, I got another compass. And I think twice before I tell someone a compass can't go bad.


Bob

Bob - ANYTHING can fail. A magnetic compass is one of those things that I would bet against failure every time, and I am confident that I would come out a big winner. Of course I would be betting money and not my life.
Electronic compasses are a different issue. I once had a gyro compass fail on me while flying with just a small amount of drift, but enough that I could have gotten into serious problems. Thank goodness (and training) there were a couple of visual references (and my magnetic compass) that kept me from flying in circles until flame-out. That's one of the reasons that I believe in redundancy.
I will say that I have never cold weather tested an oil-filled compass. Less than 6 ata is about the limit of my pressure testing of one without failure.
Cheers - M²

 

[The Chairman]

It's all about the gauss, 'bout the gauss, 'bout the gauss, where it's pointing
It's all about the gauss, 'bout the gauss, 'bout the gauss, where it's pointing.

It's all about that gauss.

It's physics, my dear Watson, and the more you learn the less you'll be surprised. Magnetism, or magnetic flux, can be caused by magnetic minerals, such as most anything with iron in it, or electricity. The closer or stronger the source, the more chaotic will be the output. Turn up the amps and the deviation will increase. Wearing your compass next to anything magnetic will affect it. Some more than others. Good news, the effects will decrease by the square of the distance. Moving your compass a foot or more away, will probably allow it to function normally, unless it's really, really big: like a wreck. That will probably require a few meters of distance.

 

[Bob DBF]

I will say that I have never cold weather tested an oil-filled compass. Less than 6 ata is about the limit of my pressure testing of one without failure.

The weather wasn't cold, the water was, but I was diving wet, and it never went to 6 ata. I don't know the mechanism of the failure, but cold water, 45 to 55 F, over 30', and some time, it got squirrly and worse as it went deeper.

I never saw a compass go bad before, didn't think it was possible, without employing a hammer, and that's why I thought the bad navigation was me, and it took forever to find the problem. With a new compass I hit a target at a few hundred yards within a couple of yards with 15-20' vis.

I just pass on the story in case in case someone looses their navigational skill for no apparent reason.


Bob

 

[flyboy08]

If you dive the poles, you'll have magnetic errors as well...and, you'll be very cold

 

[The Chairman]

I never saw a compass go bad before

A sufficient shock can demagnetize a needle. Dropping it or dropping something on it could provide that shock.

 

[Anthony Jones]

And don't forget a compass can go bad. I had one that made me think I couldn't follow a compass course anymore. It seems that on the surface before the dive it worked perfect, then when subjected to cold and pressure it would not swing properly. My buddy was on my a** about my lack of skill with a compass, until we were out of the water and it was pointing due east. When moved it was sluggish and stopped where it wanted. After a half hour or so during the SI, it worked perfect again.

Needless to say, I got another compass. And I think twice before I tell someone a compass can't go bad.
Bob

You can accidentally reverse magnetize the needle also. Had a chick one time I was diving with who used one of those magnetic octo holders. One magnet clips on your BC and the other magnet clips on the 2nd stage and they stick together to hold the octo. I liked it at first because you just had to grab the octo and pull and it came loose, nothing to unsnap or take out of a pocket. But her compass was lying on top of the thing in her dive bag one day. After that her compass always pointed south.

 

[Bob DBF]

The needle was still magnetized and worked perfectly before the dives, the problem only happened in the water, after sufficient exposure to cold and depth, it was a gradual developing problem as the dive progressed. That's what made me doubt my navigation skills, the compass did not seem to have a problem out of the water until immediately after my last dive with it.

I know it is possible to kill a compass, however I haven't seen it happen when they are protected and used as directed. I used a u/w compass I had that was left over from the '60's without issue until I bought my new Suunto.


Bob

 

[Anthony Jones]

The needle was still magnetized and worked perfectly before the dives, the problem only happened in the water, after sufficient exposure to cold and depth, it was a gradual developing problem as the dive progressed. That's what made me doubt my navigation skills, the compass did not seem to have a problem out of the water until immediately after my last dive with it.

I know it is possible to kill a compass, however I haven't seen it happen when they are protected and used as directed. I used a u/w compass I had that was left over from the '60's without issue until I bought my new Suunto.


Bob

Musta been some underwater anomaly that messed it up. We have a draw bridge here in town. It has some real huge geared electric motors on it that raise and lower it when larger boats need to pass under it. I was hunting sheepshead around the piling last year. North points inland into the inlet and south points out to the sound. When they raise the bridge your compass points to the electric motors. LOL I'm guessing induction from the windings in the electric motors cause MF interference and the steel bridge acts like an antenna when the motors are powered up.

 

[tarponchik]

I keep both compass and comp on my left hand but on the opposite sides of my wrist: comp on the inside, compass on the outside. Works OK (my comp uses a quarter-size lithium 2322 battery.

 

[MargaritaMike]

I keep both compass and comp on my left hand but on the opposite sides of my wrist: comp on the inside, compass on the outside. Works OK (my comp uses a quarter-size lithium 2322 battery.

It would be interesting to check the heading when it is on your computer wrist against the heading on the other wrist. My guess is that it will be a little different. If you are using your compass for out and in, it shouldn't make much difference because the induced deviation will be the same both ways. But what do I know?

Cheers - M²