compass for S. Hemisphere
 

Anybody have any experience using a Northern Hemisphere compass as far south
as say New Zealand? I *know* you're supposed to have a s. hemisphere
compass in an ideal world, but I'm wondering how much the card deflects i.e.
is it still useable, even if tilted.

Lin Pardey somewhere on their site told of what happened to them when they
tried such.

http://landlpardey.com/

net net, the compass was off by a considerable margin. She explains why.

Anybody have any experience using a Northern Hemisphere compass as far south
as say New Zealand? I *know* you're supposed to have a s. hemisphere
compass in an ideal world, but I'm wondering how much the card deflects i.e.
is it still useable, even if tilted.

Evan Gatehouse wrote:

Anybody have any experience using a Northern Hemisphere compass as far south
as say New Zealand? I *know* you're supposed to have a s. hemisphere
compass in an ideal world, but I'm wondering how much the card deflects i.e.
is it still useable, even if tilted.


First I ever heard of such a thing.

I can't believe it matters. A compass is a compass.

Now, if you want to talk about sundials, I can tell you there is a
difference. My birdbath was bought as a yard ornament. The wife
thought it was "cute", with a little sailboat in the middle, the
sail being the, waddaya call it, that casts a shadow on the sundial
markings around the brim.

It is made in Australia, I think, or Malaysia. The numbers are
reversed so that if the sail's shadow falls at 12:00 noon, then a
hour later, if falls on 11:00. Other than that, it keeps excellant
reciprocal time.

Now, that makes sense, since around here, there is much commotion
regarding getting horses in front of carts, etc, that sort of thing.

The pedestrians never notice, but it does set the tone for the yard.
We have 3 large trees, a white pine, a balsam fir, and a blue spruce
all crowded together fighting for space by the driveway, with a
bench huddled amongst them, a good place to ruminate while enjoying
the scent and early morning sun with a cup of tea. We call them the
Father, The holy Ghost, and the Son. I guess it's no wonder that we
got, by chance at the garden department of Kent's, a southern
hemisphere sundial to set nearby.

I just seems to fit, somehow.

It matters, but a southern hemisphere compass? Yuk, yuk, yuk!

Terry K

"Terry Spragg" wrote in message
...
Evan Gatehouse wrote:


First I ever heard of such a thing.

I can't believe it matters. A compass is a compass.

It is because the Earth's magnetic field is not spherical. It dips in as
you get closer to the poles. Compass cards are not accurate unless they are
level. From about lat 35 to 40 on up to the poles the needle tends to dip
downward as it tries to align itself with the magnetic flux. Good compass
cards are balanced to counteract this dip. When a compass set up for the
Northern hemisphere is in the Southern hemisphere the counterweight
accentuates the dip and vise versa..

I don't know if this would be any help to you, and I don't know for sure
that they still do it, but Ritchie used to sell several different compass
cards for their Globemaster compasses, weighted according to the latitude
you'd be using the compass in. I can't lay my hands on my Ritchie catalog
right now, but I recall that there was a diagram that divided the
hemispheres into a number of bands and recommended a specific card for each
of the bands. Seems to me that a card was good for a center band and one
band on each side of it without too much dip.

For a hemisperical compass (i.e., with a flat cutoff on the bottom rather
than a true spherical shape), a northern-hemisphere compass will actually
hang up on the bottom of the compass when you get far to the south, because
of the extreme amount of dip. Powerboat compasses tend to be hemisperical.
Most sailing compasses, too, I believe. Ritchie's Globemaster is an
exception.

Tom Dacon

"Evan Gatehouse" wrote in message
...
Anybody have any experience using a Northern Hemisphere compass as far
south
as say New Zealand? I *know* you're supposed to have a s. hemisphere
compass in an ideal world, but I'm wondering how much the card deflects
i.e.
is it still useable, even if tilted.

Your compass will "stick" as the bearing that the card sits on binds due to
the magnetic force of inclination tilting the card. That is, your readings
will become erratic.

If its a hand held compass, you can sometimes tilt it to allow the card to
float freely on its bearing, and still be able to use it.

Many compasses allow for adjustment. Check yours.

The problem is real, and varies with the earth's magnetic field, which does
not simply vary with lattitude. See, for example, the Silva or Suunto
compass sites for charts of the 5 compass zones that manufacturers make
compasses for. It sounds like your compass is zone1, and I think NZ is in
zone 4.

A while back I bought a set of Fujinon binoculars from the US. The inbuilt
compass is unusable here in Australia....it just sticks anywhere between
+-20 degrees off true bearing.


"Evan Gatehouse" wrote in message
...
Anybody have any experience using a Northern Hemisphere compass as far
south
as say New Zealand? I *know* you're supposed to have a s. hemisphere
compass in an ideal world, but I'm wondering how much the card deflects
i.e.
is it still useable, even if tilted.

Glendon wrote:

Your compass will "stick" as the bearing that the card sits on binds due to
the magnetic force of inclination tilting the card. That is, your readings
will become erratic.

If its a hand held compass, you can sometimes tilt it to allow the card to
float freely on its bearing, and still be able to use it.

Many compasses allow for adjustment. Check yours.

The problem is real, and varies with the earth's magnetic field, which does
not simply vary with lattitude. See, for example, the Silva or Suunto
compass sites for charts of the 5 compass zones that manufacturers make
compasses for. It sounds like your compass is zone1, and I think NZ is in
zone 4.

A while back I bought a set of Fujinon binoculars from the US. The inbuilt
compass is unusable here in Australia....it just sticks anywhere between
+-20 degrees off true bearing.


"Evan Gatehouse" wrote in message
...

Anybody have any experience using a Northern Hemisphere compass as far

south

as say New Zealand? I *know* you're supposed to have a s. hemisphere
compass in an ideal world, but I'm wondering how much the card deflects

i.e.

is it still useable, even if tilted.






Does this problem occur in fluxgate compasses also?
krj

On Saturday 23 October 2004 12:30 am in rec.boats.cruising krj wrote:


Does this problem occur in fluxgate compasses also?

No.
OTOH, you should not rely on a fallible electronic device
as your only compass.

--
My real address is crn (at) netunix (dot) com
WARNING all messages containing attachments or html will be silently
deleted. Send only plain text.

First I ever heard of such a thing.


lots of thing you never heard of before, terry.

I can't believe it matters.

believe

A compass is a compass.


**IF** you understand them, that is true. obviously, terry, you don't. a
magnetic card compass for the northern hemisphere is funcitionally different
from one for the southern hemisphere.

Chris Newport wrote:

On Saturday 23 October 2004 12:30 am in rec.boats.cruising krj wrote:


Does this problem occur in fluxgate compasses also?


No.
OTOH, you should not rely on a fallible electronic device
as your only compass.

Redundancy is good. Autopilot compass is flux gate (plus NMEA GPS
input), Richie bulkhead mounted standard compass, Davis hand bearing
compass, Wheams flux gate hand bearing compass, and compass in binoculars.

"Evan Gatehouse" wrote in message ...
Anybody have any experience using a Northern Hemisphere compass as far south
as say New Zealand? I *know* you're supposed to have a s. hemisphere
compass in an ideal world, but I'm wondering how much the card deflects i.e.
is it still useable, even if tilted.

Yes as everybody knows southern hemisphere compasses point to the top
of the world (ie Antartica) and if you use a northern hemisphere
compass it will get confused and point halfway between north and south
and head east or west.
incidently thats why captain cook discovered Austrailia by accident
when he was looking for india.

[warning this email contains Sarcasm]

"Terry Spragg" wrote in message
....
It matters, but a southern hemisphere compass? Yuk, yuk, yuk!


Come on Terry, you're not supposed to make jaxie look smart.

Compasses do indeed need to be adjusted for the Southern Hemisphere. Here's the
Ritchie comment:
http://www.ritchienavigation.com/ser...albalance.html

here's the actual map of inclination (known to mariners as "dip")
http://www.ngdc.noaa.gov/seg/geomag/icons/wmm2000i.gif
As you can see, there's a serious difference between the USA and New Zealand - plenty
to make the card jam if not balance properly.

Everything you might want to know about the Earth's magnetism:
http://www.ngdc.noaa.gov/seg/geomag/geomag.shtml

On 23 Oct 2004 02:32:30 GMT, (JAXAshby) wrote:

a
magnetic card compass for the northern hemisphere is funcitionally different
from one for the southern hemisphere.

I knew I should have played the lottery the day JAX finally got
something right and explained it without sounding like Forrest Gump.

Point made, JAX, now stand down before you strain something.

R.

rhys wrote:


On 23 Oct 2004 02:32:30 GMT, (JAXAshby) wrote:


a
magnetic card compass for the northern hemisphere is funcitionally different

from one for the southern hemisphere.

I knew I should have played the lottery the day JAX finally got
something right and explained it without sounding like Forrest Gump.

Point made, JAX, now stand down before you strain something.

R.

ok, ok, ok.

So, it's been a long time since dippy compasses were discussed in my
presence. Please pardon my forgetting a subject so long disused.

So, if your 5Kbuck compass needs heart surgurey to keep it levelled
up with a north weight instead of a south weight, why not use your
pocket silva and give it enough tilt so it doesn't bind? I've
tried it now, and it seems to work just fine with a bit of a twist
on. Mind, I'm a dippy northerner, but we're not that far north, I
guess, nor that dippy, unlike some extant.

I don't usually bother with Jakz so I had to seek out the comment
regarding weighted compass cards.

It seems to me the amount of dip in the compass reading might be
some indication that you're way north, or you are passing over the
magnetic pole or something.

If I go all that far north or south, I will remember this gem: "A
cheap hand compass can be used where a millonaire's compass cannot."
Appropriate gear for the mission, eh?

I would also bring alernative nav devices, like homing pigeons,
odour samples, wave pattern transform almanacs, depth sounder, even
RDF, LORAN, pylorous, sextant, charts, or GPS, I guess.

Mind, dipping compasses would only be needed at extreme latitudes.

Who'da thunk? I guess crossing the equator means a major compass
replacement every time you cross the line, eh? Is that what the
shellbacks do while the nymphs are getting transsubstantiated?

Does this mean I can't trust my compass card inclinometer any more?

Vapour, right?

Terry K