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    Re: GNSS is not immortal
    From: Bob Goethe
    Date: 2018 Sep 26, 15:05 -0700

    In my view, this is an argument for CN.  Term it the "Hail Mary" use of CN....

    ...a fairly shallow pool of intended users.  The pool is restricted to: ocean going recreational vessels, several days out to sea, struck by lightning, failed to have a proper faraday cage around each and every backup GPS, all were fried and the navigator has all of the necessary tools to perform CN.  

    I agree with all you have said here.  And it is indeed a shallow pool of intended users.  But a pool I have swum in, so to speak.  It took 21 days for me to sail from Hawaii to Victoria, Canada, in a 45 foot sloop.  We were not struck by lightning...but being aware of the possibilities of EMP (and also the possibility that I myself might make a mistake in the construction of my Faraday cage), I brought along my sextant, almanac, Pub. 249 and a manual, wind-up watch (in case the quartz watch on my wrist got fried).

    The wind-up watch kept different time when we were in the trade winds and the boat was pounding, from when we got becalmed one day as the North Pacific High slid to the west and engulfed us.  But I kept records of how the watch was doing once a day, compared to the quartz watch on my wrist so I could get at least a general feel for how it gained/lost time.

    I had a hand-held GPS, a hand-held VHF radio, and a second quartz watch stored in a cardboard shipping tube that I had cut down into a suitable length.  I used bubble wrap inside to keep them from banging around, and to provide electrical insulation.  Then I wrapped the outside of the tube with aluminum foil.

    ....What if that shallow pool of users includes you?

    Indeed.

    The main reason I had my sextant and assorted books on board is that I simply enjoy goofing around with sextants.  I would do this even if there were no other issues in play.

    That said, I read something years ago about the merits of keeping a life raft on board, in spite of the fact that you are enormously unlikely to ever need it:

         "You only have to sink once to gain a whole new appreciation of statistics."

    There might be a similar proverb one could propose for recreational sailors about the virtues of not depending solely on GPS.

    Bob

       
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