Compass reading 180 degrees off???

[diverdown247]

Doug, I took a dive at Aunt's Creek on Table Rock Lake in Kimberling City, Missouri on 4/28 for search and recovery of a lost prop and drive shaft.

I shot an azimuth with my compass before my descent to mark North of the bouy, which was to be my search area. Once at depth of 30-35 ft and a temp of 50 degrees, my compass was reading almost exactly 180 degrees off. I thought this seemed strange at first and continued my dive since I could see where the sun was in relation to my reference bouy. I also marked North on the bottom with a tire that was there.

For the second dive in an alternate location, I made sure to face south and watch my compass on the way down. Interestingly enough, the compass repeated this problem on the second dive in a separate location. I actually watched it spin to 180 degrees off at 30 ft.

Any ideas as to why this happened? I apologize as I did not check this issue on today's dives at Dewey Short Dam on Table Rock (teaching) where I had a specific rock wall for direction. I can attempt this again tomorrow.

I did notice some metal military runway parts in the Aunt's Creek area that may have thrown off the azimuth, but in 2 separate locations it didn't make any sense.

 

[Charlie99]

Are you sure you aren't just getting confused by the "indirect" style of marking degrees on dive compasses?

On a regular "direct" marked compass, when you are above it and looking down, 000/360 is at the North end of compass, 090 on the East, 180 on the South.

Indirect compasses are designed to be looked at from the side, so when you look down at then from the top, 180 will be at the north, 000 at the south, and 270 at the E side of the compass.

Some dive compasses have both indirect markings that you see when looking from the side, and direct markings that you see when looking down from above.

Could this 180 degree difference in style of marking the compass be the problem?

Charlie Allen

 

[Racket]

Wouldnt that make it 90 degrees off and not 180?

 

[Firefyter]

Wouldnt that make it 90 degrees off and not 180?

360-180 = 180

Opposite sides of the compass are always 180° apart.

 

[diverdown247]

Are you sure you aren't just getting confused by the "indirect" style of marking degrees on dive compasses?

Kind of difficult (unless you're the kind of person in need of a compass for dummies manual) to miss it on the Oceanic compass I have. The one I have fits the VT3 trans/compass mount. It has a HUGE arrow that points North. That and when I take my azimuth at the surface, I set my outer ring to match so I am 100% sure I don't just get turned around on a descent.

That said, I'm 100% sure it read wrong. Now, I'm not saying it couldn't be off at the surface, but correct at depth; though that is unlikely.

Also, in the VT3 trans mount, it is extremely difficult to read the compass through the side window, so I read it from the top since it's on a retractor.

 

[cummings66]

I don't know if this is the issue, but my compass (Not an Oceanic) will read 180 off if read from the top. It's accurate only if you use the window in the side to read it.

 

[visibilityunlimited]

Could it be a high iron content in the water itself. Just a hypothesis

 

[ReefHound]

I don't know if this is the issue, but my compass (Not an Oceanic) will read 180 off if read from the top. It's accurate only if you use the window in the side to read it.

But this would be true BOTH on the surface and at depth. He is saying that he is looking at it from the top and the needle is actually turning 180 degrees as he descends.

 

[The Kraken]

This confuses quite a number of people.

If you look into your side scan window, you will see your azimuth, direction of travel, heading, or whatever you elect to call it.

If you look at the compass from the top, your heading will be at THE BOTTOM of your compass (6 o'clock position).

Now, if you take your compass and roate your bezel, the ratcheting ring on the top of the compass, until the 0 on the bezel lines up with the north pointing end of the arrow on the floating part of the compass (the needle) you can read your heading at the top of the compass (12 o'clock position) on THE BEZEL.

You'll note that the red line (lubber line) passes through your heading at the top of the compass and your reciprocal heading at the bottom of the compass (when viewed from above).

the K

 

[visibilityunlimited]

I am sure that you know this already and I don't want anyone to take offense for me stating basic compass but there are also new divers that are reading this as well.
It is very important that the compass be kept level when taking the initial heading. If it is not kept level the disk (as in Oceanic's) or needle can get trapped. A common error is for the diver to take their heading at the surface treating the compass as if they were looking at a wristwatch. Once they begin their descent, everything becomes less cumbersome equipment wise and they are able to actually look down over the compass keeping it more level. That is when the compass can become untrapped.
If you are in doubt as to whether the needle is trapped either above or below water, take your initial surface heading then turn your body puposely off course and see if the needle moves. If it doesn't then it is trapped and you would need to take your initial heading all over again.
I am not this is what what happened just that it could happen. Just as a point of interest.

Does the compass in question have any air bubbles in it which may have gotten under the disk portion?