Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    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.
    | 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,
    | 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
    | 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,
    | 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
    | 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
    | the latter choice might have been more dangerous because he would have gone south of Small's
    | 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
    | 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
    | 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
    | 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
    | 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
    | via St George's Channel (between Ireland and Wales). He was coming from the general direction of
    | 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
    | 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
    | 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
    | 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
    | by Chronometer had been found by this Latitude, the ship's position would have been erroneous 31
    | 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
    | 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
    | 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.
    | 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
    | 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.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site