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    A Practical Nav Problem
    From: David F. McCune
    Date: 2006 May 23, 22:31 -0700

    I have been giving a lot of thought recently to a practical navigation
    problem.  As I mentioned on the list some weeks ago, I am preparing for a
    singlehanded voyage in a 31-foot sailboat with no navigational electronics
    from Los Angeles to Sweden via Panama.  One of the most difficult legs of
    this voyage is the piece from Panama to Florida. I'd be curious to hear
    advice from the list.
    Anyone who has a chart of the Caribbean and a North Atlantic pilot chart can
    follow along with my logic.  Keep in mind that I am sailing solo, so I have
    to sleep once in a while as the windvane steers the boat.  My boat averages
    about 125 nm per day.  Looking at the chart, you will see that I need to
    hold a course just east of north for about 60 hours.  This will take me east
    of the Roncador and Serrano banks.  Assuming I can maintain this course and
    can pass at least 30 miles east of Roncador, then at approx 14d 30'N and and
    79d 30'W I can turn NW and try to pass west of the Serranilla shoal and then
    thread a needle through the 5 or 6 mile wide deep water between the Rosalind
    banks.  (Jeez, that last bit about threading a needle gives me the willies,
    but I haven't come up with a reliably better solution yet.)
    Now a look at the pilot chart for April (when I am planning to complete this
    leg) shows winds mainly from the NE until reaching 16 or 17 deg North, after
    which the winds may have a more easterly component.  Holding a course of NNE
    into a NE force 4 or 5 trade wind (with the 12 foot swell that entails) is
    no easy matter. I've done it, e.g. when sailing due north out of Hawaii
    bound for California, but it a bone-jarring experience.  The quality of my
    sights in those conditions can leave a bit to be desired.  If I get a cocked
    hat with 5 to 8 miles per side, then I'm very happy.  Sometimes it's worse,
    depending on the seas.
    If the winds cooperate and have a more easterly component, then I will hold
    a course as close to NE as possible, perhaps even heading east of Serranilla
    (passing between it and New Bank) and then turning NW just SW of Pedro Bank.
    But the winds may not cooperate.  They usually don't.
    To complicate the picture a bit more, the chart shows a current rotating
    counter-clockwise in the area between 10d north and 18d north, i.e., north
    of the Panama Canal).  So I will be pushed eastward at 0.5 - 1.0 knots
    during the first 36 hours (that's good) and then westward after passing
    I had originally planned to do this leg in January, but decided that the
    risk of a "norther" blowing down from the Gulf of Mexico was too great.  The
    last thing I need in all of this is to be forced to tack northward.  Tacking
    in contrary seas and a changing current makes the navigation almost
    impossible.  The chance of a front and the associated north winds moving
    this far south decreases through April, though it can still happen.
    (Indeed, a norther blew into the central Caribbean just last week.  The jet
    stream was unusually far south for this late in May and an upper-level
    trough dragged the front quite far south.)
    The bright side is that the chance of overcast is quite small on this route.
    So I thought I'd time the departure so the waning moon was about 120 degrees
    ahead of the sun.  That way I will be able to get pretty good sun/moon fixes
    all day long for the first 4 or 5 days of the trip.  The stars and planets,
    of course, are only available twice a day, so having a moon at 90 degrees to
    the sun (as occurs on April 10, 2007) is a godsend.
    (Why, you might ask, not wait another two weeks until the moon is waxing?
    That way I'd have the sun/moon 90d fix for the first few days and then have
    a full moon and better visibility the rest of the leg.  Well, that means
    putting the leg off until around the 21 of April.  Not bad in and of itself,
    but I need to depart from Miami for England no later then May 15 or 20 in
    order to get out of the western Atlantic before hurricane season.  And I
    suspect I'll have some repair work to do on the boat once I get to Florida,
    so I want to get there as early as possible, preferably by the 20th of April
    or so.  Of course, this may be a demonstration of the old question:  what's
    the most dangerous thing on a small boat? Answer: a calendar.)
    One thing to keep in mind is that the declination of the sun during the
    first half of April is from 5 to 10 deg N (and increasing), which means it
    will be fairly close to the zenith.  In my experience, that makes it harder
    to get latitude from a noon sun site.  The moon's declination in April of
    2007 will be 0 on April 1 and rapidly moving south, so latitude by moon
    get's easier with each passing day.
    Once past the Rosalind banks, I should be able to head straight for the
    western tip of Cuba, after which I can turn NE and make for Key West, being
    pushed along by the Gulf Stream.  Other than other boats, there is nothing
    much to hit during that part of the trip, so the navigation doesn't worry me
    so much.  It's the first 4 or 5 days out of Panama that are scary.
    Any thoughts or ideas?
    PS.  Anyone who suggests taking a GPS along should get banned from the list

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