Re: [Paddlewise] Really Decent Compass Units?

Colin Calder wrote:
> 
> I use a Ritchie deck mounted compass, but also carry a silva 'orienteering'
> style compass. [snip] While I agree
> that a deck mounted compass is the best tool for taking bearings from a
> kayak and holding a course, the silva compass/protractor is extremely useful
> in a kayak for taking bearings and distances from a chart/map, and is always
> there for use as a spare compass.
> 
> For those of you who don't carry a silva style compass, how do you take
> bearings from your chart ???

Good point, Colin.  I use a special protractor made by Weems and Plath.
When its long dimension is aligned with the desired course, it gives the
course bearing as a direct reading off lines pre-drawn on the chart to
be parallel to the direction of magnetic north.  This device is 11
inches along its longest dimension and gives more accurate bearings than
the much smaller Silva style compass.  It is cumbersome enough that I
mainly use it in camp before paddling.  The Silva would be more
convenient on the deck of the yak.

> Compass trivia: ever tried to use a silva style compass manufactured for use
> in the Northern hemisphere in the southern hemisphere, or vice versa? Lines
> of magnetic force do not run parrallel over the whole surface of the earth,
> at the poles for example, the magnetic force is *down*. The needle of a
> compass is balanced to sit horizontally in which ever magnetic zone it was
> designed to be primarily used in, and for a Northern hemisphere compass the
> balance is on the wrong end of the needle in the southern hemisphere, where
> it sits irritatingly against the base plate.

The dip of the magnetic lines of force at my latitude (46 degrees N) is
substantial -- maybe 20 degrees -- that's a lot of counterbalancing! 
Won't traditional deck-mounted compasses of the direct-reading style
(like the Ritchie or the Aquameter) have the same problem when used in
the "incorrect" hemisphere?

-- 
Dave Kruger
Astoria, OR
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