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Drawing magnetic variation lines on chart


JohnHuth

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Spot on John, and exactly how I prepare my charts. When no compass rose on my printed chart (e.g. NOAA booklet charts), I'll use my orienteering compass as a protractor, picking out a near-central N-S grid line as reference to mark my first magnetic line, then continue E and W with tick marks and additional magnetic lines.

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That's very clever, marking it out in NM and using that parallel thingie. I have always just drawn parallel lines with a ruler, and figured close enough was good enough. I will keep your method in mind.

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  • 1 month later...

I'm testing out a purely graphical way of teaching vectors - this is first part in a series. It's not for everybody, but when we got to figuring how to find ferry angles at the REI navigation workshop, I realized that it was a bit much for some folks. Maybe some math-averse people might want to take a look and give me feedback.

Link here

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I'm testing out a purely graphical way of teaching vectors - this is first part in a series. It's not for everybody, but when we got to figuring how to find ferry angles at the REI navigation workshop, I realized that it was a bit much for some folks. Maybe some math-averse people might want to take a look and give me feedback.

Link here

>>Note that you won’t be able to get the ruler perfectly aligned with the northing axis, but using the tick marks and a bit of effort you can get decent results.

If the compass base plate is large enough you can use it to drop a perpendicular from the tick mark to each axis.

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>>Note that you won’t be able to get the ruler perfectly aligned with the northing axis, but using the tick marks and a bit of effort you can get decent results.

If the compass base plate is large enough you can use it to drop a perpendicular from the tick mark to each axis.

Yup, that would work, too. The main point is that I wanted to give people the idea that there is some imprecision introduced when making these graphical solutions. Thanks for reading it!

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Next in series: adding vectors

Again, the main point here is to give purely graphical solutions people can work with, using a backpacker's compass. To keep the clutter down in the figures, I used a protractor and ruler, but you should be able to see how to substitute a compass.

Looks good, John. I wouldn’t put it past you if you could graphically demo Stokes’ theorem. :)

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For those of you who might be interested, I'm hosting a symposium on navigation on Nov. 14th (a Friday) at the Radcliffe Institute for Advanced Study (Harvard Sq.) - it's an all-day event, open to the public. Now, this probably will *not* help you with your kayak navigation skills, although who knows.

We'll have talks on the neural basis for cognitive maps (Nobel prize this year in Medicine got it), the behavior of lost persons, animal navigation, culture and navigation, and the far out ideas like using pulsars as an interstellar GPS navigational system.

Here's the link to the symposium

Edited by JohnHuth
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Vector subtraction using a current problem as an example

I know, you probably have to be pretty hard-core to do this, but here's a quote of one of the aims of the 5* navigation syllabus:

  • To apply the above relevant information in calculating vectors and negotiating open crossings and/or coastlines with no landing zones and/or tide races and overfalls

Ah-ha….so the 5* guys are supposed to know vectors…sez here…..

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