UKC

Hi, Can anyone tell me how a Southern hemisphere compass differs from the ones used in europe, and I guess the northern hemisphere in general. (a mate at work just came and asked me as he is off to new zealand in october

Cheers Steve.

In reply to moonraker:

"For a compass to work properly, the compass needle must be free to rotate and align with the magnetic field. The difference between compasses designed to work in the northern and southern hemispheres is simply the location of the "balance", a weight placed on the needle to ensure it remains in a horizontal plane and hence free to rotate. In the northern hemisphere, the magnetic field dips down into the Earth so the compass needle has a weight on the south end of the needle to keep the needle in the horizontal plane. In the southern hemisphere, the weight needs to be on the north end of the needle. If you did not change the weight, the needle would not rotate freely, and hence would not work properly. "

You can get ones that work in both hemispheres (balanced) or just buy one in the hemisphere you intend to use it

Don't normal compasses work anyway in that the South point of the compass is attracted to the Earth's magnetic south pole, and so lines up in the same way? I'm thinking they must do, and at the equator, there is equal influence from the Earth's N & S magnetic poles, so they'd line up in the same way as well. Just a theory!

In reply to Gareth James: They do to a point, but it points down into the housing, I've used Northern Hemisphere ones down there and you had a reasonable idea of North, but I wouldn't want to walk on a bearing with one. Best option is too buy another one down there, or a one that can be used in both hemispheres. We ended up buying one there, then moved back again, so bought a new one that does both.

In reply to OP:

Just for info - I took a northern compass to Patagonia. 2 years ago. It got a bubble in it but seemed okay.

Just realised last week though it is 10 degrees out (compared to others' compasses). I'm assuming it's because of the bubble. More worrying though is the fact that I never noticed I was always 10 degrees off!

In reply to moonraker:

It's a bizarre thing, and please excuse me for floating off at a tangent on your thread, but many years ago I went to a lecture by someone from Silva. Besides the balance thing, which makes sense and I'm sure is true, he also said that compasses have to be calibrated for the part of the world they are to be used in. People don't say that any more, and I've been wondering why not. I assume it's because magnetic north has been drifting further and further towards true north over the past twenty years so that maybe the calibration thing is not necessary now. But it follows logically from that, that the age of a compass is important regardless of where it was bought. So I guess it's wise to throw out old ones.

In reply to Alison Stockwell: I thought some compasses still needed that?

In reply to moonraker:

It would appear to me, from all your answers, that you all need a lesson in the correct use of a map and compass. Learn the difference between True and Magnetic North. Check the date of your map, check the magnetic variation for that year - and the current year. Find a suitable spot to 'swing' your compass.
During my working life I relied on a 100-year-old ship's compass for my regular fishing trips up in the Arctic Circle and beyond. I use that same compass here in the Southern Hemisphere with no problems at all. Just plain and simple navigation.
Dumping old compasses? Pah.

In reply to moonraker:

Quick google give this http://www.steiner-binoculars.com/downloads/SteinerCompassZones.pdf

In reply to bergalia: But a ship's compass is big and is designed to be used anywhere I assume. Small Silva style compasses do come in Northern and southern versions due to the balancing of the needle. Not sure how much difference it actually makes though.

In reply to bergalia:

There's no need to be so patronising old boy.

The information about the movement of magnetic north that most of us take for granted is a gross over-simplification. Futhermore, not all international maps have such detailed or up-to-date information as OS ones do.

100 years is a long time in the wandering life of the North Pole.

See here

http://gsc.nrcan.gc.ca/geomag/nmp/long_mvt_nmp_e.php

In reply to moonraker:

As has been said before, the needle needs balancing to work correctly. It will point to magnetic north, but the needle will deflect downwards, which may mean to have to point the compass down to get the needle to rotate correctly. If I was relying on it for accurate navigation I'd get a specific model for the correct region.
Ships compasses are on gimabals anyway, as they're designed to cope with tilting ships, so you can't really compare the two.

In reply to bergalia: Bergalia I think you misunderstand me.

I nowhere mentioned magnetic variation as this isn't what it is about.

Use a 'normal' NH silva compass in the SH and you do get a rough idea of where North is, but I wouldn't want to micro nav with it. It does point through the housing. you can jiggle about and get a good level of confidence, but if I need the campass that much, I'd rather spend the extra £20 and get a compass that I know is spot on.

In reply to IainRUK:

I think he was reponding to my off-topic musings about the fascinating movements of the magnetic north pole and it's possible implications. Apologies for being such a nerd.

In reply to Alison Stockwell:

PS this page is even more fascinating.

http://gsc.nrcan.gc.ca/geomag/nmp/long_mvt_nmp2_e.php

In reply to Ridge:

Ships have their compass on gymbals, some have them on gyrocompass but most use GPS for normal operations anyway.

They also have to be corrected for use on a particular ship by adjusting the metal balancing balls.

http://en.wikipedia.org/wiki/Compass#Compass_balancing

In reply to nz guy: I ahve an old South African Compass, but assumed it was knackered, as the needle never lay flat. Now I know wy.

In reply to bergalia:

And why you you want to swing a compass if you're on foot? The only reason to do it is if you're on a very large metal object (a ship, for example) that will variously interfere with the magnetic field as it (the ship) points in different directions. Hence Sutty's large steel balls and an assortement of other metal placed around ships' compasses to negate these extraneous influences (their position and size being calculated while swinging the compass).