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I would like to thank Herbert Prinz for a well-argued reply to my question
about the choice of time-argument in the early Nautical Almanac.

Trevor Kenchington wrote, with other interesting comments-

>I do have Greenhill & Hackman's "Herzogin Cecilie" (1991), which
>includes some quotations from that ship's logbook in the hours leading
>up to her stranding in 1936. Those clearly used the civil day (changing
>24 to 25 April at midnight). Thus, I would tend to agree with George's
>scepticism. Before withdrawing any suggestion of such a late use of the
>nautical day, however, I would note that the same logbook says that they
>"Changed the ship's time to land time at 2100 hours" of the day that
>they arrived off Falmouth for orders. Most likely, that was either a
>matter of correcting their reckoning for small accumulated errors in
>their chronometer time or perhaps an adjustment of the watch schedule to
>match GMT rather than local apparent time. However, it remains possible
>from this limited evidence that the ship had been using the nautical day
>during her blue-water voyage from Australia and changed to the civil day
>on arriving in coastal waters.

It seems likely likely to me that the phrase "Changed ship's time to land
time at 2100 hours" really did imply that they changed from a noon-to-noon
reckoning on the log to using midnight-to-midnight civil time. But what
causes Trevor to think that the noon-to-noon reckoning could have been by
the Nautical Day, 12 hours ahead of the Civil Day, rather than by the
Astronomical Day, 12 hours behind the Civil Day? That's what I am trying to
establish; the era in which Nautical Time finally fell out of use.

George.


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