Calling any MAPRICs!

Discussion in 'The Training Wing' started by Proximo, Jul 5, 2006.

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  1. There must be a reasonably competent MAPRIC out there who can provide an educated response to this thorny and baffling problem.

    My mate is a Aussie over on some contrived attachment. He has brought his compass with him. Problem - it doesn't work - in fact, it doesn't even turn. Upon further investigation, none of the Aussies on our camp have working compasses either.

    So, what's causing it? They work fine in every other respect - no air bubbles, cracks or crap in the oil - and the discs are free floating.

    Any ideas? Are they specially calibrated to ignore everything except South Magnetic Pole? Seems a little unlikely...
  2. Had a look at an Aus site via Google, says that compasses may not work in the Northern hemisphere but doesn't say why.
  3. Maybe positioned too close to alternating current?

    Were all the compasses transported together? Silva-type or prismatic (i.e. enclosed in a metal case)? (Not that answers to these will give me a better idea of the cause, but they may explain why they all choose to do the same thing).

    I would have expected there to be an air bubble. Its absence may be indicative that the casing has compressed, jamming the spindle. If transported as hold baggage (as opposed to being in a pressurised cabin), leakage of the air bubble in flight could cause such compression when back on the ground. They may revert to normal over time if the seal on the casing is just weak enough to allow air passage but not the more dense oil.

    IIRC, compasses, containing magnetic components, should travel as cabin baggage.

    Can't be anything to do with the hemisphere as UK compasses work in FI.
  4. Spanish_Dave

    Spanish_Dave LE Good Egg (charities)

    Re: Beware the compass
    The posting is almost totally correct. I would be very sure that the compass should really be bought for the latitude that it is intended to be used at. I suspect that this is more important the closer the compass is to the poles. A compass bought for use near the equator should be able to be used in either hemisphere. Near the equator, the earth's magnetic field lines are approximately parallel to the earth's surface. But, near the magnetic poles, the field lines are almost vertical to the earth's surface. In operation, the compass needle lies along the earth's magnetic field lines. Thus, at the magnetic pole, the needle would be almost vertical. The compass manufacturer adds weights to the compass needle so that it will lie horizontally at the latitude he intended it to be used at. This is so that the compass needle will not scrape the glass above or the scale below it, and can move freely on its pivot point. I would think that any given compass should work over a reasonable range of latitudes. Any compass will always point to north but, a high northern latitude compass will probably have to be held a long way off horizontal for it to move freely in the southern latitudes. North is always north, for any compass.
  5. EXBQMS: Can't this be overcome just by slightly tilting the compass?

    And Aus is at approximately the same magnitude of latitude as UK. (Well, +/- 30 degrees)

    edited to add: I bit, didn't I. :oops: Mental note: Must read the links before I comment on posts.
  6. Ever wonder what the letters on the reverse of the compass baseplate means? it's to do with the area the compass can be used properly, check the manual of land navigation or whatever the hell it's called,
    it shows "bands" which refers to the letters. NS
  7. Cheers Box - I will do this tomorrow! :D
  8. Spanish_Dave

    Spanish_Dave LE Good Egg (charities)

    Does anyone remember Boris the lunatic instructor from the MAPRIC course
  9. Puttees - that is also truly amazing!

    Behold!!! The power of ARRSE!
  10. As a follow-on,though, does the British Army hold stocks of differently-balanced prismatics, presumably with different NSNs? Or is it just a superb compass that is particularly tolerant?

    I ask as I once did a 6 mile road survey in FI (Zone 4) with prismatics taken from UK (Zone 1) (theodolites got bust in transit) and the final error was less than a few metres. What I don't know is whether we had FI-balanced compasses.
  11. Great Bloke:)
  12. Who could ever forget the Boris, his compass collection & trusty sidekick(when I was there) Simmy. Madder than a box of frogs, but as you say top bloke, I still tell recruits about the pylons!
  13. Spanish_Dave

    Spanish_Dave LE Good Egg (charities)

    The pylons, would that be change of direction by any chance? :eek:
  14. Have you tried standing on your head and using it?