compass

"David Walker" <wbsdavenews@hotmail.com> wrote in message
news:bqartd$egg$1@wisteria.csv.warwick.ac.uk...
> > The bane of boyscouts, as they attempt to navigate with, or without, the
> > benefit of their trusty compasses, is the fact that this Pole chooses to
> > roam about in a 20-mile circle, and to shift its course between day and
> > night.
>
> And occasionally (not in any of our lifetimes I don't suppose, can't
> remember how regular it is - certainly the thousands of years) it decides
to
> flip completely, so N=S, and S=N, just to confuse people... apparently!
No
> idea where I got that from though!
>
It can be predicted. The next time it is due to flip is not that far off.
Not in our life-time, but not far outside it iirc.

<Pete S.> wrote in message
news:3paisvo1jnmgqv89meu7btb2i85gjv4ail@4ax.com...
> On Sat, 29 Nov 2003 18:24:20 +0000 (UTC), "Nigel Hewitt"
> <nigelh@REMOVETHISnigelhewitt.net> wrote:
>
> >david wrote:
> >> "Nigel Hewitt" wrote
> >>> david wrote:
> >>>>> Why do compasses not work ?
> >>>> here more
> >>>
> >>> Grief. Two posts on the subject and both show that you'll believe
> >>> anything. I must sell you something.
> >>
> >>
> >>
> >> I was not losing a lot of sleep over it But did not want ask a
> >> question with out looking first and the second you press send you
> >> find a better or different answer.
> >
> >Thank you for the smilie.... I admit I'm a bit crunched after the flight
> >back from Hurgarda. I'll be nicer tomorrow but today I hate everybody
> >and everything.
> >
> Hurgarda? Kids stuff. Got off the plane friday morning after steerage
> passage from Aukland to London, with a three hour stop in Singapore.
> In the air for 24 hours. And I have an exam on monday morning.....
>
> Pete S.

Auckland? you been down here in NZ?

you see the Poor Knights?

rhys

On Sun, 30 Nov 2003 15:35:34 +1300, "rnf2" <rnf2@NOSPAMwaikato.ac.nz>
wrote:

>> Hurgarda? Kids stuff. Got off the plane friday morning after steerage
>> passage from Aukland to London, with a three hour stop in Singapore.
>> In the air for 24 hours. And I have an exam on monday morning.....
>>
>> Pete S.
>
>Auckland? you been down here in NZ?
>
>you see the Poor Knights?
>
The Poor Kinghts? Never met a poor one yet!!

We went south, to the mainland......

NZ is a beautiful country, but there are problems with diving in NZ.

1 I represented 10% of the CCR diver population in NZ.

2 If you go into a dive shop and say words like Nitrox, Trimix,
Deep, Wreck, CCR, they have a wobbly.

3 All divers in NZ want to do is kill things.

Apparently there are now 9, CCR divers resident in NZ. That is
according to Pete Mesley of Dive HQ in Aukland, who has trained or
dived with most of them. He says there are some really good wreck
dives around in less than 100m of water, but that Kiwi's just want to
kill things. Hence the proliferation of camouflage wet suits and spear
guns.

I went into several "dive outlets", asking "What kind of diving do you
do here?" to be told "anything you like". When I went on to explain
the type of diving I do, there was much shaking of heads, and comments
like "but we have a 15m bug hunt this afternoon, from a bendy boat..."
Bendy boats and spear fishing, what a combination!! Barbie on the boat
next.......

There were some open minded dive shops though. Dive HQ (very good -
the only techie place in NZ) in Aukland, dive shops in Kaikoura,
Nelson etc., but overall you have an education problem with your
diving. And OSHA, your equivalent of the HSE. They don't like people
decanting Oxygen. Apparently it's very, very dangerous... Dare I tell
them what I do in my garage?

I'll be back...... compared to Europe, it's lovely.

Pete S.

"Nigel Hewitt" <nigelh@REMOVETHISnigelhewitt.net> wrote in message

> Compasses don't work in wrecks, unless they are very old and made of wood
> and at Wraysbury. Even in wooden wrecks you can find pig iron ballast
making
> them go round in circles and Wraysbury.... well I think that Richard just
annoyed
> the Gods of Diving somehow that they did it just to stop him running
navigation
> courses.
>
> nigelH
>
>

I am convinced that the electrified railway running next to Wraysbury lake
dosen't help much. The magnetic field caused by the train motors is also a
variable error.

Keith

>I am convinced that the electrified railway running next to Wraysbury lake
>dosen't help much. The magnetic field caused by the train motors is also a
>variable error.
>
>Keith
>
Richard told me once that there were power cables or the like running
under or near (can't remember) the lake there.. helped in my
explanation to my buddy at the time (yes, it does happen) as to why I
couldn't find the exit platform despite taking three readings at the
surface! :D

rich

"Nigel .
>
> Yes, a compass in the north of the northern hemisphere does tend to tip
down
> due to the 'dip angle' and vice versa. Fortunately the people who make the
> things know this and displace the pivot above the centre of mass of the
card
> and all is well. If they did it by weight the weight would need to be
adjusted
> by latitude so a Spanish compass would not work in Scotland and a ship
> would be stuffed when away from home. Even if a dive compass was a bit
> sensitive to the dip angle would it matter? You hold it in your hand so it
turns
> freely so you are compensating.

Actually this matters quite a lot, although admitedly diving is a bit more
rough and ready so it matters less than for hillwalking say.

Take the extreme case of standing at the North (magnetic) pole a compass
will be pointing straight down (or is that up?). At the equator it'll be
flat. In the UK say, something in between, ditto Australia only the other
way. A UK compass is barely usable in Oz. It took me a couple of months to
twig why mine was behaving oddly when I lived there. If you check the Suunto
website you'll see they do different models for different latitudes. It is
possible to have a self-compensating one, whereby the magnet bit can pivot
vertically, within a pointer constrained horizontally (if that makes
sense). I doubt if you can get a "diving" compass like this.

An earlier poster seemed to be underestimating magnetic variation - can
often be in the 5 to 10 degree range, rather than 20 miles out at 4000 miles
away as someone suggested. But as Nigel said, wouldn't matter if you're
just going along and back.

Cheers

Hywel

> An earlier poster seemed to be underestimating magnetic variation - can
> often be in the 5 to 10 degree range, rather than 20 miles out at 4000
miles

Yeah - if you look at charts for the south coast, the variation from North
is currently just over 4 degrees, and is actually coming back closer to true
North by 8 minutes per year (8 60ths of a degree) so in a few decades true
north will be the same as magnetic north, from the UK at least.

> away as someone suggested. But as Nigel said, wouldn't matter if you're
> just going along and back.

Yeah, most people can't swim to within a few fractions of a degree -
somewhere within about 10 degrees is usually close enough for most purposes.
Even if you did bother to compensate for the shift, you would likely be out
by about twice that angle anyway just because you can't follow angles
perfectly..... and most people i've seen using compasses have been sat right
next the the Stanegarth in Stoney, and swim in completely the wrong
direction.

David


PS - Stoney was lovely on Saturday for those who don't usually like diving
in mud holes! Viz was fantastic! I could see my DSMB on the surface from
below 18m around the Wessex, looking out over the side of the Stanegarth we
could see loads, and that was after it'd been open about 4 hours! And in
one dive we managed to find just about everything on the 20m shelf, from
Stanegarth, a mini (which i've never been to before), the bus, landrover,
wessex, some railway carriage base (how long's that been there by the way?),
a white van, then come up and see most of the 6m shelf too! I never knew
Stoney could be so nice!

> *ahem*....
>
> Temperature @ Stoney? Find it or share it @
> http://stoneytemps.calumscott.me.uk/

Hehe
To be fair, I did try to have a look at that earlier in the week, but
couldn't find it - I still had the old address for it.
I've added it in now for you though! :O)

David

"David Walker" <wbsdavenews@hotmail.com> wrote in message
news:bqf3hr$52o$1@wisteria.csv.warwick.ac.uk...
> > *ahem*....
> >
> > Temperature @ Stoney? Find it or share it @
> > http://stoneytemps.calumscott.me.uk/
>
> Hehe
> To be fair, I did try to have a look at that earlier in the week, but
> couldn't find it - I still had the old address for it.
> I've added it in now for you though! :O)
>
> David

Thank you very much.

CAS
--
PADI AOW? Get Rescue Training on UKRS Course #1 -
http://divesite.calumscott.me.uk/ukrs/rescue_diver_2004
Temperature @ Stoney? Find it or share it @
http://stoneytemps.calumscott.me.uk/

Pete S. <> wrote in message >

I went into several "dive outlets", asking "What kind of diving do you
> do here?" to be told "anything you like". When I went on to explain
> the type of diving I do, there was much shaking of heads, and comments
> like "but we have a 15m bug hunt this afternoon, from a bendy boat..."


Blimey, hope we don't bump into bugs that big, when we are out there in Feb

Sorry, couldn't resist.

Snash