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    Re: Modern CN Ditch Kit
    From: John Huth
    Date: 2012 Jul 23, 19:00 +0200
    Catching up here on a couple of topics.   "Ditch kit" depends in part on what I'm doing.   Since I don't do a lot of offshore sailing (but wish I could) it means that the need for reliable backups is not huge, so I get to play around.  

    Normally when I'm sea kayaking, I'm just a compass and map guy.   I do make a regular habit of dead-reckoning by counting paddle strokes and also have a habit of using the Sun as a time and azimuth marker.   When I go backpacking, I will frequently ditch the compass and try to use shadows from trees to create a natural compass - this typically means I have some sense of the path a shadow will take on that date at that latitude, but it's worked pretty well on a few trips.   

    Regarding Emergency Navigation - I'm in fairly regular contact with David Burch.   I have come up with an alternative to that klunky way of memorizing the equation of time.    

    Here's my method - just remember "Chocolate 14 16".    The idea is this "I'm the Sun.....I like chocolate....the two days of the year when chocolate is most relevant to me is Valentines Day and Halloween.....Because I like chocolate, I'm slow to part with it, and quick to pick it up.....accordingly on Valentine's day, I'm late by 14 minutes, and on Halloween I'm early, but by 16 minutes...."  

    Then draw those points, put a flat-top of +/- 2 weeks, then advance from Valentines Day by 3 months, go 4 minutes early, and then retreat from Halloween by 3 months, and go 6 minutes late.

    For me, this is much easier to remember than that ditty that David quotes.   

    The other issue in David's book is his sinusoidal approximation to the declination of the Sun.   If you use that, you can be off by as much as 1.6 degrees.   I have also a kind of trapezoidal approximation that I've memorized to make up the difference between the sinusoidal approximation and a closer approximation to the declination.   It's clearly an average over years, but it works well enough to get you down to about 10-15 arc minutes in figuring declination.   

    Finally, on the homemade quadrant issue, I've made one by subdividing 90 degrees by bisecting angles using the usual construction we learned in geometry class.   The one I made was good to about 20 arc-minutes, as good as the declination approximation.      

    With a good watch, I was able to get a precision of about 20 nm in latitude and 15 nm in longitude using the equal altitude method.   This was in October where the departure from a sinusoid for the declination is quite large.   I could probably do a bit better around the solstices.

    JH


    On Sun, Jul 22, 2012 at 5:11 AM, Thomas Sult <tsult@mac.com> wrote:

    What is in your CN ditch kit?...

    A GPS, VHS radio and a Cell Phone and a small solar charger. When venturing off shore a satellite communication device. My full CN kit is on the boat. If I need a ditch kit I am interested in modern technology just like my fore fathers, their ditch kit had the latest and best technolog, so does mine. 
    Tom. 

    Thomas A. Sult, MD
    Sent from iPhone

    On Jul 21, 2012, at 13:37, Greg Rudzinski <gregrudzinski@yahoo.com> wrote:



       
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