NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Joshua Slocum's navigational methods
From: George Huxtable
Date: 2005 Apr 17, 10:04 +0100
From: George Huxtable
Date: 2005 Apr 17, 10:04 +0100
Frank Reed revisits the question of Slocum's navigation. I was (somewhat reluctantly) convinced by his arguments, in that earlier correspondence in 2003, to the effect that there's no evidence of more than a single lunar-distance observation in Slocum's whole circumnavigation. And in describing that observation, Slocum showed such delight and pride in it, that if he had taken other lunars on other legs of the voyage, he would surely have at least mentioned them. So I now agree with Frank, that over Slocum's solo voyaging, there's no further evidence of reliance on lunars than that one example. Yes, he would have used dead reckoning: but the shorter and slower a vessel is, and the longer she takes on an oceanic passage, the more uncertain DR becomes. Slocum's advantage was that he was navigating at a time when (as well as the trade wind system) ocean currents were becoming understood, thanks mainly to Maury's work. And Slocum had a lifetime of ocean-going experience to draw on. When a ship's captain, his longitudes had been taken from on-board chronometers, at least in the later years of his career, though he had kept up his skill in finding longitudes by lunars. Well into the 19th century, though, it was common for the smaller trading vessels to do without that expensive chronometer, and not all shipmasters could manage lunars. The alternative was latitude sailing, a technique which had been adopted by mariners for hundreds of years. In latitude sailing a landfall, at the other side of an ocean, was planned, if possible at a spot which was benign in terms of no offlying rocks, and a coastal profile in which soundings would warn of a closing approach. After putting the vessel on that latitude, long before the expected arrival, and sailing East or West, a vessel could hardly fail to reach her landfall eventually: though without knowledge of longitude, the date of arrival would be a matter of guesswork. My presumption is that Slocum did much of his navigation that way, which didn't rely greatly on accurate dead reckoning.. George. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================