NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2018 Dec 17, 07:42 -0800
Frank,
You wrote:
“Navigators did not worry about taking sights on the prime vertical for local time except in relatively rare cases.”
This is borne out by what Joseph Hart writes but may not be as broadly true as your statement suggests. I was recently motivated to look into this matter and found that in the log of Shackleton’s vessel, Endurance, an effort is clearly being made to take the time sights on the prime vertical whenever possible. I suspect that this is a required procedure in some Royal Navy manual that Frank Worsley was following. It would be interesting to know if it is available somewhere. Below are a sample of time sights made underway.
Time Sights | ||||||||||
Date | Altitude | Latitude | Longitude | Azimuth | ||||||
° | ʹ | ° | ʹ | ° | ʹ | ″ | ||||
15 Aug 1914 | 20 | 32 | 43 | 18 | N | 10 | 54 | 9 | 89.5 | |
17 Aug 1914 | 23 | 54 | 39 | 54 | N | 12 | 37 | 29 | 91.9 | |
18 Aug 1914 | 22 | 51 | 38 | 18 | N | 13 | 31 | 5 | 90.8 | |
04 Sep 1914 | 23 | 59 | 19 | 1 | N | 23 | 43 | 29 | 90.2 | |
04 Sep 1914 | 15 | 25 | 18 | 7 | N | 24 | 16 | 58 | 272.8 | |
10 Sep 1914 | 20 | 3 | 7 | 59 | N | 24 | 22 | 16 | 87.3 | |
03 Nov 1914 | 21 | 14 | 50 | 15 | S | 40 | 56 | 22 | 271.9 | |
04 Nov 1914 | 38 | 17 | 52 | 12 | S | 38 | 21 | 34 | 61.6 | |
04 Nov 1914 | 39 | 4 | 52 | 13 | S | 38 | 32 | 41 | 60.3 | |
04 Nov 1914 | 50 | 16 | 52 | 25 | S | 37 | 39 | 51 | 27.1 | |
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This is not a complete or comprehensive study. The sights were chosen more or less at random. A typical day consisted of an AM time sight and a noon sight. When a morning time sight was not possible, presumably because of weather, a PM time sight was made. The three time sights on 4 November were made a day before arriving at Grytviken whaling station on South Georgia and may have demanded more frequent sights than on the open ocean.
As back story to this; motivated by this report https://www.bbc.com/news/science-environment-43703723 Lars Bergman and I looked into Frank Worsley’s original log books to understand how well the position of the wreck of the Endurance is known. We submitted our conclusions to the Journal of Navigation . In the course of its preparation we were informed that our paper was being proof read by a very senior officer of the Royal Navy who had wondered why Worsley was not making his time sights on the prime vertical around the time of the sinking. My initial reaction to the comment was that “Navigators did not worry about taking sights on the prime vertical for local time except in relatively rare cases” but thought I’d better check. All this suggests to me that it is standard procedure in the Royal Navy to take time sights on the prime vertical when feasible. Maybe the is some altitude cutoff rule that goes along with it,
Regards,
Robin Stuart
