Northern and Southern Hemisphere Compasses

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Northern and Southern Hemisphere Compasses

Post  skookumchuck on Fri May 15, 2009 11:53 pm

Yes Reg is quite right. ( Getting lost in the bush - quote from gof2 )
We were out the back of Ora Banda with a bunch of guys detecting last year, pennyweights mob. I followed a track then went along a fence line looking for some indications of mining. I found a couple of patches of dry blown but didn’t turn up anything. As it was overcast and starting to rain lightly I decided to head back to the vehicles. I got the bearing on my gps to the vehicle waypoint and rather use the gps as it was an old Eagle Sportnav, good gps but rather large in the hand and uses up batteries, I orientated myself with my wrist compass that I got whilst I was in the army in Vietnam. Being overcast and in whipstick country it was hard to see in what direction I was going. After travelling for about half an hour I opened my gps to check to see how far I’d come. Instead of 5 kms away when I started I was 6kms away !! I reverted to my gps and made it back to the main track and one of the crew we were with picked me up as he was heading back to camp and dropped me off at my vehicle. I was relaying my story around the campfire about how I was puzzled that I was heading the opposite way with my wrist compass. ‘Young’ Reg asked me where I got he compass and I told him it was a US army issued one. He said ‘That’s your problem, it won’t work in the southern hemisphere’. We all looked at each other and said ‘crap! north’s north. ‘
‘Check and see’, he said, ‘If you buy a compass from a shop overseas or ebay , you have to state whether you want to use it in the northern or southern hemisphere .’
As we didn’t believe him we got our compasses out and sure enough mine read the opposite way. We were all bewildered but we learnt something that night. My wrist compass had a floating face like you see on a boat and read the opposite way to all the others. I also had a needle one which also got in the northern hemisphere but I just read the half coloured needle to line up with north and south with that colour. Blue in the northeren hemisphere pointing north if I was there but down in Australia blue pointing south in the southern hemisphere.
Thanks to ‘young’ Reg I can now explain to my fellow colleges in 1976 when I was in college doing an orienteering run how we came in last and way behind time !! Puzzled me all those years as I was sure we were going the right way !

Last edited by Jefgold on Mon Jun 01, 2009 8:22 pm; edited 1 time in total (Reason for editing : Correct Heading)


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North is North, Right?

Post  forester01 on Mon May 18, 2009 4:18 pm

G'day Skookum,
mate you were right first time - north really is north - whether you're in the northern or southern hemisphere makes little difference to the bearing your compass should be giving you to march on. 'True North' and 'Grid North' will certainly be different of course given magnetic declination and grid differences, but 'Magnetic North' remains constant, and at the moment mag north is located somewhere in far northern Canada I believe, so a ship's navigator operating somewhere in the Bering Sea would need to know what he was about. Don't know what sort of compass you were using (apart from being US issued that is, which could mean it was a 'Brunton', a good compass and a favourite of theirs) but you should have stuck to the issue Aust Army prismatic, the old faithful, which I also used in SE Asia. I can assure you that we went right ahead and used the same compasses on our return to Australia (Holsworthy in my case) no difference at all.

I currently use an Iris 50 Plastimo prismatic purchased from a Florida firm. Immediately on receiving it I checked it out for reliability side by side with two other compasses I own on a non metallic surface (not too close of course) - one a Silva orienteering model, the other being of Finnish make, the brand-name I don't recall at the moment - Heikenen perhaps?) All three pointed accurately to magnetic north in the same way with no deviation twixt the three (I live in central Victoria which is well and truly in the southern hemisphere). Incidentally, always follow the red arrow shaped end of the mag pointer - that's where north is. Someone considerably wiser than I on the topic of map reading once told me when I'd led a group into geographical embarrassment, 'Trust your compass, trust your map - it's usually the operator who's wrong headed'. In the meantime I use the US-made Plastimo regularly and have encountered no problems. Only problem with it is that it has no built-in protractor base plate which is usually encountered with the better Silva models.

However I believe there CAN be a difference between a compass usually manufactured for use in the northern hemisphere - which apparently means that allowance has been made for a possible 'dip' downward at the arrow end of the pointer bar to a lesser or greater degree as it points 'through' the planet toward mag north. We'll also have that problem here but its normally considerably lesser and overcome by obtaining a compass with a sufficiently generous fluid filled body for the arrow or compass card (face) to rotate on without having the north pointer 'bottom out' on the base of the compass. Think of the weight and depth of the issue AMF prismatic compass (which you would certainly have been given instruction on in whichever RTB you trained at, Pucka or Singo and you'll see what I mean).

I agree with your statement of a few posts ago - namely that the GPS is a good standby, but navigation is all about best use of compass, map and protractor.

All the best

Mike W

Last edited by forester01 on Mon May 25, 2009 1:03 pm; edited 3 times in total (Reason for editing : To get it right.)
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