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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)

gl

On Aug 27, 2:19 am, "George Huxtable" 
wrote:
> 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...@huxtable.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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