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    Backup Celestial Navigation Kit
    From: Robert VanderPol II
    Date: 2015 Apr 30, 15:10 -0700

    So what would everybody put in a package for the ultimate backup celestial navigation getup?

    Basic scenario: half way across the ocean of your choice you are hit by lightning and every piece of electrical and electronic equipment on the boat is fried.


    Try to keep the costs down to encourage the hoi polloi to think this is a reasonable expenditure.

    Try to keep things as simple as possible so folks won’t be discouraged from practicing once a week or so.

    Try to minimize weight and volume to . . .

    You all get the idea.

    This is intended to get someone home or to a port where repairs can be made, it isn’t intended to be able to continue a voyage to a difficult landfall with lots of outlying dangers.


    Here’s my idea:

    Davis Mark3

    3 mechanical watches

    G.Kolbe Long Term Almanac, tear out the sun & stars almanac and laminate them with instructions and star map.

    Moon almanac printed on waterproof paper for several years to come including laminated correction tables.

    Rite in the Rain notebook

    Plotting sheet printed both sides and laminated

    Two sun, 1 moon and 3 star worksheets printed together front and back on a single sheet and laminated.

    Brown-Nassau Celestial computer or failing that the flat LoPook/Bygrave sheets.

    Grease pencils and/or erasable markers in fine point.



    Prior to voyage the watches are wound daily at the same time and rates of error are established.  These errors are tracked in the Rite in the Rain.  If one is really on the stick some effort is made to determine error thru the range of the sextant.

    Underway everything is pulled out once a week and a single sight is shot (not a noon sight) and the GPS MOB button is pushed at the same time.  The sight is worked and plotted.  After the fact the GPS coordinates are retrieved and plotted to give feedback on how close the LOP is to the MOB.

    So then the unpleasantness occurs.

    In the worst case the watches were let to run down and time is lost.  Wind them and set them to the same time making a best guess as to what the time might be.  To regain at least semi-accurate time shoot the moon and a few other bodies.  The moon needs to be significantly east or west of your position for this to work well (let’s say 30degrees east or west of true north or true south).  You should get some vague agreement among the misc. bodies with the moon line even further out.  Add or subtract a set amount of time to all of the sights and recalculate.  The rule of thumb is 2 minutes of time for each minute of longitude disagreement between the moon and the ‘fix’ for the other bodies. After the first 2 cycles you should be able to interpolate or extrapolate.  If the moon line is to the west add your correction, if east subtract the correction. When the moon agrees with the rest of the fix you have figured out how big the error was for your best guess of time.  You have re-established time.  Would probably be good to immediately or the next day reshoot a round including the moon and double check the time correction.  Thereafter recheck weekly.  In a lightning strike I would worry that the high magnetic fields might affect the watches rate of error so that should be tracked over time.


    This method of regaining time is not of my own devising, it is from John Letcher’s book on navigating with HO-208, a good read all around though I did not come to adore 208 the way he did.

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