A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sumner's Line (Navigation question)
From: Ken Gebhart
Date: 2006 Feb 8, 21:51 -0600
From: Ken Gebhart
Date: 2006 Feb 8, 21:51 -0600
On 2/2/06 9:46 AM, "George Huxtable"
wrote: > 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. > > contact George Huxtable at firstname.lastname@example.org > or at +44 1865 820222 (from UK, 01865 820222) > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.George. > George, Thanks for the response. I am sorry to be late in acknowledging yours and others responses, as I just returned from the Chicago Sail Boat Show and was involuntarily off line for a while. The morning after posting my question, my palm hit my forehead as I realized I was actually SELLING the Line of Position Book you suggested. And yes, it answered the part about navigational procedures which dictated going from light to light until clear of danger. However, it did not answer the second part which asked why disaster was averted. You pointed out that Bowditch did not include that comment which is good to know. But someone made it (perhaps only for dramatic effect), so I still want to pursue it a little further. Several posts agreed that it was not perilous since he was 31 min west of his DR, etc.. But, has everyone missed this, as my reading puts him 31.8min EAST (or closer to The Smalls light, and the rocks), or am I wrong? Is it reasonable to make a case that being closer than he thought was courting disaster had he not discovered the LOP? PS. As an aside, I am pleased to report to the group that a very great interest in Celestial navigation was experienced during the above mentioned show over the past ones. Many of the comments made to me were in line with the "zen" posts made by Lu Abel. One young man said "God, that is just the coolest thing you can do on a sailboat". Our booth was fairly swamped at times, and the seminars on CN were as well attended as any. Just thought you would want to know. Ken