Schoonertrash wrote:

The first answer was the closest. Yes there is a difference and yes in most
compasses including the one's we find on our sailboats and powerboats are,
in fact, different. Some compasses, such as the one on USNS Bob Hope, are
built to be self adjusting when crossing the line.

Sounds like a good but probably expensive feature to have.

.... The easiest way to
solve the issue is order up a compass from some company in Australia, NZ
etc. and have it airmailed. Get the exact same compass you already have.

Actually, you don't need to order from Australia (not intending to hurt the
Aussie economy, sorry). All good compass makers will have the same model compass
made in several dip ranges. The dip angle changes by latitude, not just when you
cross the equator.


When crossing the equatorial region at some point you will observe the tilt
or dip. Switch compasses and re-swing. ..... The reason it happens is the
distance from
the mass of iron in N. Canada that is the Magnetic Northern Pole increases
while the mass of earth's iron making up the Magnetic Southern Pole
decreases in distance. At some point one becomes the major attraction to ye
olde compass instead of the other and it becomes off-balance.

Total malarkey. Compasses are polar, north poles & south poles of magnets both
attract metal but only opposite poles of other magnets. Try it yourself with a
kids toy bar magnet.

The reason for the dip angle is that the Earth is round (well, it's an oblate
sphere) and the lines of magentic force between the North and South Poles are
more apple-shaped. So, the Earth's magnetic field pulls either the north or
south pole of the compass card down more as it approaches the poles.

Here's the
humorous part. When the compass on our ship acted up none of the highly
trained and experienced deck officers realized what had happened. One of
the other AB's remarked to me, "Southern Dip?" "For sure", sez I. Finally
we were asked what we meant by that phrase. They didn't believe us and had
to look it up in Bowditch. Score one for the home team!

I guess if you don't think about a compass very often, you forget stuff like
that. I can't believe a qualified sea officer would have never learned about
compass dip. For that matter I am surprised you can't explain it more clearly &
accurately yourself, ST!

Fresh Breezes- Doug King