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    Re: Basque Whalers
    From: Lu Abel
    Date: 2013 Mar 11, 10:25 -0700
    Bowditch teaches (or at least used to teach) lots of navigation-by-soundings techniques.  One particular (and peculiar) technique was to take a run of soundings, plot them on a piece of transparent paper, and slide it around on your chart until your soundings fit the chart and you'd know you were somewhere near the last sounding.

    Even in this age of GPS, I think there are some "sailing by soundings" techniques that are useful (especially if my GPS is flaky).

    1.  I remember as a newbie sailor making my first coastal voyage.  Fog rolled in just as I cleared a buoy, visibility down to less than 1/4 mile.  Next buoy up was about 15 miles away.  This was pre-GPS and when a Loran receiver cost close to the price of a new car.  I looked at the chart and saw that the mark was on the three fathom contour.  Add two feet for state of the tide and I steered to keep my depth sounder showing 20 ft.  Sure enough, the buoy popped out of the fog as expected -- aha, another Christopher Columbus moment for me!

    2.  A very classic technique when approaching a harbor in the fog when there are smooth contours and no hazards along the shore is to deliberately set course to go one side or the other of the mouth of the harbor and then change course to run parallel to the shore along the contour of the entrance buoy.  Nantucket harbor, the old whaling capitol of the US, is a classic case; I've personally used this technique almost every time I've ever visited it because the fog almost inevitably rolls in just as one clears the offshore buoy about five miles from the harbor's entrance.


    From: Andrés Ruiz <navigationalalgorithms---.com>
    To: luabel{at}ymail.com
    Sent: Monday, March 11, 2013 6:28 AM
    Subject: [NavList] Re: Basque Whalers


    Frank wrote:
     “The Banks themselves are shallow and can be navigated by soundings (see the movie "Captains Courageous", for some navigation by soundings and some amazing sailing, too).”
    Yes, if the soundings follow the coastline you can sail following it until landfall. For me was very useful one day with thick fog. Because the uncertainty and shoals is dangerous, but if the coast is well known, is useful.
    In the same way, if latitude is known, and calculating the magnetic variation by Polaris, one can navigate using a magnetic chart  (see: magnetic variation navigation.PNG
    By the way, I found the movie in a library, I remember seeing the movie when I was a kid. I hope I enjoy with it again.
    -- 
    Andrés Ruiz
    Navigational Algorithms
    http://sites.google.com/site/navigationalalgorithms/
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