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    Re: Wartime (WW2) navigation
    From: George Huxtable
    Date: 2010 Jan 31, 20:24 -0000

    Thanks to Trevor Bell for providing the numbers, on which this list feeds.
    However, someting is wrong with the longitude of his first waypoint, which
    is given as 15d 00m W. When Trevor has corrected the typo of the missing
    digit, it will be worthwhile taking his problem further. An interesting
    problem it seems to be.
    For the voyage-leg that Trevor is considering, from Cuvier to that first
    waypoint, I suggest any master would feel quite justified in treating it as
    a Mercator, or even more simply, a middle-latitude, rhumbline sailing
    problem, rather than working it as a great circle, the difference in
    track-length being pretty negligible. Even if he had been instructed by the
    Navy to take a great-circle path to that waypoint, he may not have taken any
    such instruction too literally. After all, his security would be enhanced if
    nobody but himself knew his exact intended track.
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: "Trevor Bell" 
    Sent: Sunday, January 31, 2010 4:32 PM
    Subject: [NavList] Wartime (WW2) navigation
    Thanks to everybody for your responses to my original post. Everybody wants
    more detail so here goes:
    Rangitane left Auckland for Panama under the direction of the naval control
    service (NCS). After passing Curvier light (36d 25m S,175d 47m E) the first
    waypoint was to be 38d 00m S, 15d 00m W, the next 32d 00m S, 130d 00m W
    before heading for Los Santos point 7d 30m N, 80d 00m W.
    Rangitane was sunk (recorded by three sources) at 36d 58m S,175d 22m W - an
    estimated position under prevailing conditions. The captain had been
    instructed by NCS to take a great circle track between the waypoints. By my
    simple calculations this puts the sinking almost exactly 50nm north of the
    nearest great circle path to the first waypoint. Had Rangitane sailed a
    direct great circle route to Panama (not via waypoints) she would have been
    sunk about 38nm south of that route.
    My question about sailing great circle or rhumbline is pertinent because,
    under interrogation at a subsequent enquiry, the Rangitane captain said that
    they might have sailed a Mercator route to the first waypoint, not great
    circle as required by NCS. If so, were the sinking coordinates on such a
    rhumbline - and, in the absence of charts, this is where I am struggling for
    a calculation.
    The underlying question is - did the Germans find Rangitane by design or by
    chance? Rangitane would have been sailing on a heading of about 090 while
    the Germans were sailing on about 010 - from ship logs they were definitely
    not shadowing her. If the Germans had been told Rangitane's departure time,
    course and waypoint, how come they intercepted her so far off course in
    total darkness? From other expert advice I have already discounted the
    possibility of radio direction finding.
    Thanks glapook for the attachments - I will have a go at the tables and
    thanks to everybody else for comments and links. There is clearly a wealth
    of information out there!
    Trevor Bell
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