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Old 22-01-2014, 06:43   #1
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H W Tilman

I have recently been re reading some of Tilman's fascinating accounts of his deep sea voyages on the sailing Bristol Channel pilot cutters during the 50s and 60s. His navigation equipment was basic and he preferred not to have things like echo sounders , RDF or even a radio. He did have a chonometer and sextant though and worked out star and sun sights via the tabulalated systems as illustrated in the US Hydrographic Office publication HO 211. A 50 page book. , in conjunction with the British Nautical Almanac. On one voyage a crew member used to supplement Tilmans "sights" by taking his own and working up by what Tilman humourously referred to as " time honoured methods employing logerithms, haversines and Cosecants". I was seafaring myself in the 50s / 60s and am pretty sure that the crew member's system would be the so called Marq.St Hilaire intercept method which was most commonly used and perhaps still is.
I have a copy of the Nautical Almanac dated 1994 wherein there is laid out an explanation of a "quick" and accurate system for calculating position line and azimuth and assume that this is what Tilman used. I don't know whether I am just "past it" or missing something here but having attempted several examples of working up a sight by this tabular method I am left with the result that it is a most complicated, finicky and time consuming procedure when compared with the M. St H. mathematical system.
I just wondered out of interest if anyone would care to comment on this and the current systems for finding position. Or does everyone now use the satallites?!
gybefive
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Old 22-01-2014, 08:07   #2
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Re: H W Tilman

Greetings and welcome aboard the CF, gybefive.
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Old 22-01-2014, 13:15   #3
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Re: H W Tilman

One should not confuse the Marcq St-Hilaire method (a mathematically sound implementation of Sumner's empirical 'discovery' published 1843), first published in 1875 with the availability of precomputed sight reduction tables such as the US HO 208 (1928), HO 211 (1931), HO 214 (1936) and the later (post-WWII) celebrated HO 229, not to mention their British AP equivalents or the shorter versions for air navigation. The St-Hilaire method was quickly adopted everywhere.
Now the computations involved: in many countries (e.g. France) the use of log tables, or short tables based on the Haversine formula, was still taught long after WWII in the merchant realm as well as in the Navy,
These computional algorithms were thus well-known and required only one cheap small booklet rather than several hefty and expensive volumes, hence their lasting popularity and use.
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