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    Re: The shipwreck of Admiral Shovell
    From: Gary LaPook
    Date: 2007 Sep 17, 00:50 -0700

    You state that the Scillies were plotted ten nm north of their true
    positions. I am looking at Edward Wright's chart published in 1599,
    more than one hundred years before the disaster. Bowditch (1962 ed.)
    gives the modern position of Bishop Rock as 49� 52' north and 6� 27'
    west and of the Lizard as 49� 58' north and 5� 12' west each of which
    are confirmed by Google Earth. Wright's chart gives the latitude of
    the Scillies as 49� 55' north only 3 nm north of the true position.
    The latitude of the Lizard on Wright's chart is 50� 00' north, two nm
    from its correct position. What chart was Shovel using that had less
    accurate latitudes than Wright's chart?
    Also interesting is that Wright has a scale of longitudes using Cape
    Verde as the prime meridian. Using Wright's chart he gives the
    longitude of Bishop Rock as 8� 20' east while modern longitude gives
    it as 11� 04' east of Cape Verde. (Cape Verde is 17� 31' west of
    Greenwich.) Wright puts Bishop Rock 121 nm west of its correct
    position which isn't too bad using Cape Verde. Wright put the Lizard
    at 10� 05' east of Cape Verde so 1� 45' east of Bishop Rock. The
    modern difference is only 1� 15' making a 30' difference, an error of
    19 nm.  (I will scan this chart in tomorrow)
    On Aug 27, 2:19 am, "George Huxtable" 
    > Frank wrote-
    > | Here's a link to the file George provided:
    > |http://fer3.com/arc/img/Clowdisley_Shovel_1707_JIN_1960.pdf
    > |
    > | For convenience, I also inserted a direct link at the end of the archive
    > | copy of the previous message.
    > |
    > | Is this article under copyright? If so, please let me know in a couple of
    > | weeks.
    > =========================
    > from George-
    > Thank you Frank.
    > I hope readers will take a serious look at it. It's a salutary tale of the
    > dreadful state of Royal Navy navigation, in 1707. How things had changed by
    > Cook's day, half a century later!
    > Not entirely their own fault, of course. The concept of longitude, as a
    > quantity that could be specified for locations around the world, with some
    > common reference-point (perhaps at Greenwich), hadn't really sunk in then.
    > Instead, mariners thought about changes in longitude, with reference to
    > their starting point, derived from their dead-reckoning.
    > But what I find so surprising are the discrepancies in latitude, in a fleet
    > that was sailing together as a convoy. As long as the Sun shone at noon (and
    > it had been doing so, reasonably often) latitude should have been clear-cut.
    > Well, limited by the precision of their backstaffs, to perhaps 15 minutes or
    > so.
    > And not helped by the scandalous errors in charts, in the days when these
    > were commercial ventures, before the Admiralty Chart existed. How many ships
    > were lost because the Scillies, and Lizard, were plotted on the chart nearly
    > 10 miles North of their true position, I wonder?
    > There's a decent gap, enshrined in the words of the old song, "Twixt Ushant
    > and Scilly is thirty-five leagues ...", or 105 nautical miles. That was what
    > mariners had to find their way between, and without even lighthouses, in
    > early days. In the days before longitude could be measured, they had to do
    > it by latitude sailing, taking deep soundings to establish how close in to
    > the Western channel they had got. In thick weather, even latitudes were
    > unavailable. That situation remained true, until radio aids became available
    > (in the 1930s ?). I wonder if Henry Halboth can recall approaches made
    > without even radio DF help, and how ships then managed, in prolonged thick
    > weather?
    > ================================
    > Frank asked about copyright-
    > Yes, that paper is only 47 years old, so I suppose that copyright
    > restrictions apply, strictly speaking, and I should really have pointed that
    > out. Readers should respect that. It has here been made available for the
    > purpose of academic discussion, but should not be disseminated further, and
    > it might be wise for Frank to make it unavailable again after it's had time
    > to serve its purpose.
    > George.
    > contact George Huxtable at geo...---.u-net.com
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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