NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Deviation Card with GPS
From: Robert Eno
Date: 2006 Jul 23, 22:58 -0500
George wrote:
> I am astounded at the complications people have got into in doing so,
> in non-steel vessels..
>
> First, I ask; is it really wise to use corrector magnets to zero out
> the deviation? All that's needed is to chuck out any corrector
> magnets, note what the deviation actually is, at each heading, make
> out a deviation card to correspond, and allow for it by a bit of
> mental arithmetic.
I agree in principle on this George, however, there are conditions under
which it is wiser and more sensible to use corrector magnets to bring the
deviation down to as close to zero as possible. A case in point would be
when the deviation changes by large amounts from one sector to another. To
quote a book I have, "as the boat yaws and pitches, the poor compass will
try to follow its errors". The result is a compass that spins uselessly as
one changes heading.
George wrote:
> Robert Eno finds his deviations to reach 25 degrees, which ought to be
> a cause for concern. If I were in his position I would go carefully
> around the boat with a hand bearing compass to search out a better
> position for the steering compass, if possible, and to understand why
> it is so badly affected. We have to remember that he is in a region of
> very high magnetic latitude, where the field is nearly straight up and
> down, and the little horizontal component of field that remains is
> likely to be badly affected by any steel around, such as his engine.
> The rest of us, in lower latitudes, have an easier time.
Robert responds:
You are correct about the horizontal vs. vertical component of the magnetic
field up my way. I should add that a handbearing compass as used by a hiker,
works perfectly well up here. Problems begin when one is confronted by rogue
magnetic influences. It doesn't seem to make much to overcome the already
weak horizontal component of the geomagnetic field.
Thanks for that tip George. I am going to try to locate the culprit in this
manner and see what I can find. I will be happy to report back to the group
if I am able to determine the cause of this huge deviation.
George wrote:
> But why not compare the compass reading with the bearing of a
> celestial body, particularly one that's low, near the horizon?
Robert responds:
Ah George, if only that were possible. It will not be until mid to late
August that any stars will be visible from up here. Even when they are,
August is the beginning of the stormy rainy months. We just can't win up
here!
George wrote:
> On my boat, I do my very best to keep things simple.
Robert responds:
On mine too, notwithstanding the big chunk of diesel engine which requires
more care and maintenance than a new bride. And of course this means having
to carry spare everything and 200 pounds of assorted tools.
It appears that my query is generating lots of interesting discourse. Keep
the ideas coming gentlemen.
Robert
--~--~---------~--~----~------------~-------~--~----~
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To , send email to NavList-@fer3.com
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From: Robert Eno
Date: 2006 Jul 23, 22:58 -0500
George wrote:
> I am astounded at the complications people have got into in doing so,
> in non-steel vessels..
>
> First, I ask; is it really wise to use corrector magnets to zero out
> the deviation? All that's needed is to chuck out any corrector
> magnets, note what the deviation actually is, at each heading, make
> out a deviation card to correspond, and allow for it by a bit of
> mental arithmetic.
I agree in principle on this George, however, there are conditions under
which it is wiser and more sensible to use corrector magnets to bring the
deviation down to as close to zero as possible. A case in point would be
when the deviation changes by large amounts from one sector to another. To
quote a book I have, "as the boat yaws and pitches, the poor compass will
try to follow its errors". The result is a compass that spins uselessly as
one changes heading.
George wrote:
> Robert Eno finds his deviations to reach 25 degrees, which ought to be
> a cause for concern. If I were in his position I would go carefully
> around the boat with a hand bearing compass to search out a better
> position for the steering compass, if possible, and to understand why
> it is so badly affected. We have to remember that he is in a region of
> very high magnetic latitude, where the field is nearly straight up and
> down, and the little horizontal component of field that remains is
> likely to be badly affected by any steel around, such as his engine.
> The rest of us, in lower latitudes, have an easier time.
Robert responds:
You are correct about the horizontal vs. vertical component of the magnetic
field up my way. I should add that a handbearing compass as used by a hiker,
works perfectly well up here. Problems begin when one is confronted by rogue
magnetic influences. It doesn't seem to make much to overcome the already
weak horizontal component of the geomagnetic field.
Thanks for that tip George. I am going to try to locate the culprit in this
manner and see what I can find. I will be happy to report back to the group
if I am able to determine the cause of this huge deviation.
George wrote:
> But why not compare the compass reading with the bearing of a
> celestial body, particularly one that's low, near the horizon?
Robert responds:
Ah George, if only that were possible. It will not be until mid to late
August that any stars will be visible from up here. Even when they are,
August is the beginning of the stormy rainy months. We just can't win up
here!
George wrote:
> On my boat, I do my very best to keep things simple.
Robert responds:
On mine too, notwithstanding the big chunk of diesel engine which requires
more care and maintenance than a new bride. And of course this means having
to carry spare everything and 200 pounds of assorted tools.
It appears that my query is generating lots of interesting discourse. Keep
the ideas coming gentlemen.
Robert
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
