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    Re: Sumner's Line (Navigation question)
    From: George Huxtable
    Date: 2006 Feb 3, 14:00 -0000

    This is a resend of a resend.
    
    Joel Jacobs states that his recent messages to Nav-L have failed to get through, and that seems to
    have happened to me also, in my response, followed by a repeat, to Ken Gebhart's posting about
    Sumner. And yet, another posting from me about Sumner, responding to Fred Hebard, sent this morning
    at 11:19 GMT, has been successfully posted. What is going on?
    
    Below is the message that I sent at 10 33 GMT this morning, once again, hoping that third time will
    be lucky.
    
    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    
    | Yesterday, 2 Feb, at 15:46 GMT, I posted a reply to Ken Gebhart's question about Sumner's line.
    |
    | I can always rely on getting such a posting reflected back to me as an email message from Nav-L,
    but
    | this time it didn't happen.
    |
    | Chuck Taylor has since sent a posting on that topic, and from that I judge that he didn't receive
    a
    | copy of my posting either. I wonder if anyone did. Perhaps it has been somehow interpreted as spam
    | by the Nav-L input filter. I wonder if Dan Hogan can comment.
    |
    | Anyway, best I can do is to send it again, as follows-
    |
    | =====================================
    |
    | Ken Gebhart wrote-
    |
    | I am looking for help in understanding something about Thomas Sumner's event during which he
    | discovered his line of position.  Space does not permit recounting the details of his situation,
    nor
    | a drawing of the navigational plot of his attempt to find Small's light.  However, this is covered
    | in detail in Bowditch and many other navigational books.  At the very end of the recount it says"
    | The DR position was found to be in error by 8 min too far south, giving a longitude of 31 min, 30
    | sec too far west.  The result to the ship might have been disasterous had this wrong position been
    | adopted". My question is howso?
    |
    |
    |
    | Can anyone tell me from historical insight of navigational procedures what course Sumner would
    have
    | set had he not questioned his first position?  In other words would he have turned to go straight
    | through St. George's Channel, or would he have turned to acquire Small's Light first? I can see
    that
    | the latter choice might have been more dangerous because he would have gone south of Small's
    light,
    | and his eta would have been upwards of 2 hours late, catching him off-guard when land (or rocks)
    | appeared. But there were the Saltees Rocks light and the Tusker Rock light off the coast of
    Ireland
    | which would have given him some protection had he opted to go straight for the Channel.
    |
    |
    |
    | This is not just a pedantic question I have.  I talk about this situation in my seminars to show
    how
    | his line of position was discovered, but thankfully no one has questioned me about exactly how a
    | disaster was averted.  Any comments are welcomed.
    |
    | ====================
    |
    | Response from George.
    |
    | First, Ken should acquire a copy of "Line of position navigation" subtitled "Sumner and
    | Saint-Hilaire, the two pillars of modern celestial navigation", by Michel Vanvaerenbergh and Peter
    | Ifland, Unlimited Publishing, 2003, $13.99, ISBN 1-58832-068-5. Peter is a member of our list and
    | occasional contributor, and also author of that wonderful book about navigational instruments,
    | "Taking the stars". His book about the position-line contains, in good facsimile, the complete
    text
    | and plates of Sumner's original article of 1843, with intelligent explanatory notes, and a host of
    | stuff about St-Hilaire's improvements on Sumner.
    |
    | Please forgive a bit of pedantry to start with. The light Sumner needed to see (well, the
    lightHOUSE
    | actually, as it was daytime) was not "Small's light", as both Sumner and Ken refer to it, but "The
    | Smalls light", named after the lethal group of low rocks and reefs that it protects against.
    |
    | Sumner's passage was from Charleston (South Carolina) to Greenock (Western Scotland, on the
    Clyde),
    | via St George's Channel (between Ireland and Wales). He was coming from the general direction of
    the
    | Azores, and had no observations since about 1500 miles back, except for a single sounding,
    | presumably South of Ireland. So, he was relying on his dead reckoning. Sumner had a nice beam
    wind,
    | from a SouthEasterly direction, but that would have made the SouthEast corner of Ireland, with its
    | Tuskar Rocks, a nasty lee shore. Presumably, then, he would wish to keep to the Welsh side of St
    | George's Channel, to preserve his freedom to act in an emergency.
    |
    | Sumner describes the weather as boisterous, and very thick. This is important. The hidden Smalls
    | Rocks lie on the Welsh side of the passage, but a ship can readily keep clear of them as long as
    she
    | can see the lighthouse tower in time. However, if the weather is too thick, unless a vessel is
    | heading straight toward that lighthouse, she might sail past without seeing it, and get into the
    | middle of those rocks before realising it. There are also other rocks too, further East, off that
    | coast.
    |
    | What Sumner's 10 am position line told him was the exact course to keep to reach the Smalls light.
    | As long as he trusted that observation, he could sail straight toward it and be sure he would
    reach
    | the light before he was in danger from the rocks around it. And so it turned out. The Smalls
    | lighthouse was seen "close aboard" (so only just in time). Then, Sumner knew exactly where he was,
    | and the rest was easy.
    |
    | Ken wrote-
    | "At the very end of the recount it says" The DR position was found to be in error by 8 min too far
    | south," giving a longitude of 31 min, 30 sec too far west.  The result to the ship might have been
    | disasterous had this wrong position been adopted". My question is howso?"
    |
    | It's strange, but I can't find those actual words in Sumner's account. Did he write it out
    | elsewhere, I wonder? Or are those Bowditch's's words, perhaps?
    |
    | Sumner actually wrote- "The Latitude by dead reckoning, was erroneous 8 miles, and if the
    Longitude
    | by Chronometer had been found by this Latitude, the ship's position would have been erroneous 31
    1/2
    | minutes of Longitude, too far W, and 8 minutes, too far S. .." The next sentence, that Ken
    | attributes to Sumner,  (and may be somewhat over-dramatic) seems to be absent from Sumner's own
    | text.
    |
    | Sumner was describing a common state of affairs round our coasts (as he points out), with bad
    | visibility near the horizon but taking advantage of a momentary glimpse of the Sun.
    |
    | Ken asks what he would have done had he not been able to deduce that "Sumner Line". I think he
    would
    | have tacked about, standing off and on, to mark time (as he had done the previous night), holding
    | position until the weather cleared enough to allow him to tackle the St. George's passage with
    | comfidence. I doubt if there was any great imminent danger.
    |
    | That's my own view, but others may put a different slant on it. It will be interesting to see
    what's
    | offered.
    |
    | ==================(end of copy of earlier message)
    |
    | Chuck Taylor's reply is to-the-point, and we appear to agree completely.
    |
    | He usefully wrote-
    |
    || Sumner's own comments on the situation may be found
    || in his book, reproduced courtesy of the University
    || of Michigan, at
    ||
    || http://www.hti.umich.edu/cgi/t/text/text-idx?c=moa;idno=AAN0447.0001.001
    |
    | I was unaware of that copy, and have since taken a glance at it, without downloading the whole
    | thing. Perhaps I will do that at a time of cheaper phone rates, as I am on a dialup line.
    |
    | It doesn't seem identical to the copy printed in full in the Vanvaerenbergh - Ifland book, in that
    | (at least) the page numbering seems to differ. Perhaps they are copies from different editions.
    What
    | I have is a copy of the 1843 edition.
    |
    | Chuck and I have agreed that the comment-
    |
    | "The result to the ship might have been disasterous had this wrong position been adopted".
    |
    | was over-dramatised, and I wonder if he or Ken can tell us where those very words can be found, as
    I
    | can not locate them in my copy of Sumner.
    |
    | George.
    |
    | contact George Huxtable at george@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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