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    Re: The Nautical Day
    From: Joel Jacobs
    Date: 2004 Feb 10, 06:21 -0500

    I did some less than scientific research by reading some ship's logs, and
    references thereto that
    appear on the internet. Some examples are the Schooner Atlantic, the German
    sub 593, and various clipper ships.,
    In all instances, the "Nautical Day" seems to be grounded in navigation, and
    not in watckeeping or work days. I draw this conclusion on the basis that
    all the references to Day's Run are Noon to Noon. This is the distance run
    calculated on celestial observations as in the refernce posted below.
    My recollection is, in the USN and Merchant Marine, the day's work for
    ship's company,
    as distinguished from "those standing watch" always started after "Morning
    Quarters" in the Navy or around 0700 in the MM.
    I then found a confirming reference.
    From the web:
    The Ship's Day: Time, Watches and Bells
    "Historically, the ship's day began at noon, when, weather permitting, the
    ship's position was fixed a mid-day with the sun at it's highest point above
    the horizon using a solar sighting device such as a quadrant or sextant. The
    twenty-four-hour day that followed was divided into watches, measured by a
    four-hour sand glass kept at the door to the captain's cabin and guarded by
    a Marine sentry, and then into half-hour intervals called 'glasses',
    measured using a 30' (sand) glass: Each time the 30' glass was emptied, the
    glass would be turned by the Midshipman of the Watch and a Marine Sentry
    would ring the Ship's Bell. Knowledge of the present watch plus coupled with
    the number of bells last rung conveyed to both officers and crew the time of
    "The naval system of starting the day with the afternoon first had the
    of putting ship's time 12 hours behind Greenwich time, so for example the
    afternoon of lst April 1800 was the same on ship and land, but the ship's
    next morning was 1st April 1800 while it was 2nd April by land. However this
    anomaly was eliminated by the admiralty in 1805 with ships time being
    brought in line with Greenwich."
    More information from this site can be found at
    Joel Jacobs
    ----- Original Message -----
    From: "Royer, Doug" 
    Sent: Monday, February 09, 2004 12:22 PM
    Subject: Re: The Nautical Day
    > The ships' day still begins and ends at local noon at sea and while in
    > port.This is mainly done for work and watch standing purposes and has
    > nothing to do with navigation.Most likely a traditional carry over from
    > earlier times.
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Joel Jacobs
    > Sent: Saturday, February 07, 2004 04:00
    > Subject: Re: The Nautical Day
    > The internet is probably the best research tool man ever had. It would be
    > worth everyone's while to learn how to use it. Of course to get targeted
    > results you do have to know how to couch you're query.
    > Doug and Stacy, isn't it true that the Nautical Day is not dead? When I
    > doing my navigating, and by training, it was and likely still is the
    > convention of most all mariner's to calculate their "Day's Run" from "Noon
    > to Noon". Logically, there doesn't seem to be much sense behind that
    > tradition because, as has been discussed here in great depth, there is
    > difficulty in using the noon sight to determine longitude. So unless your
    > course is mainly N or S, you get little help from the LAN sight except as
    > advance your morning LOP, the result being an EP, not a fix. Now if you
    > the time to do so, and change you course to put the sun dead astern, you
    > will always get an accurate LOP from which to calculate the Day's Run.
    > In any case, the tradition is still with us, and as I pointed out it comes
    > from a British Admiralty mandate around the time of Cook's voyages.
    > Joel Jacobs
    > ----- Original Message -----
    > From: "George Huxtable" 
    > To: 
    > Sent: Saturday, February 07, 2004 5:43 AM
    > Subject: Re: The Nautical Day
    > > The Nautical Day
    > >
    > > What a wonderful source of information is the internet in general, and
    > > Nav-l in particular!
    > >
    > > Thanks for all the informative replies to my question about the Nautical
    > > Day. They have certainly corrected some erroneous notions of mine on
    > > topic. The references to the website
    > >  were
    > > particularly helpful.
    > >
    > > I thought I was reasonably familiar with Cook's journals of his three
    > great
    > > voyages, in the Beaglehole edition, and was aware that he had changed
    > > time-scale on arrival at King George's Island (his name for Tahiti) in
    > > April 1769. What he wrote then in his journal was-
    > >
    > > "Note. The way of reckoning the Day in Sea Journals is from Noon to
    > > but as the Most material transactions at this Island must happen in the
    > Day
    > > time this method will be attended with inconveniences in inserting the
    > > transactions of each Day; for this reason I shall during our stay at
    > > Island but no longer reckon the day according to the civil account, that
    > is
    > > to begin and end at midnight."
    > >
    > > And so he did. But there's an ambiguity in Cook's wording, which fooled
    > me.
    > > In that passage he doesn't spell out whether the days in the sea-journal
    > > were kept 12 hours in advance of the civil day (the nautical day), or 12
    > > hours lagging behind it (the astronomical day). He presumed that every
    > > reader would realise that it was the former. Because, for his
    > > he was relying on the new-fangled Nautical Almanac, I had wrongly
    > > that his sea journal would refer to the astronomical day, because that
    > > what the almanac used as its time-scale throughout.
    > >
    > > Looking at the detailed sequence of dates as he arrived at Tahiti, and
    > > departed, it is indeed clear that he was using the nautical day when at
    > > sea. In fact, Beaglehole makes the matter perfectly obvious in a "Note
    > > the dating", placed just before Cook's Journal starts in Vol. 1, in
    > > he says-
    > >
    > > "The dating of the Journal is according to 'ship time', by which the
    > > twenty-four hour day begins twelve hours before the day of civil time,
    > > runs from noon to noon. Cook's p.m. therefore precedes his a. m., and
    > > a.m. alone is identical with civil a.m. Thus hid Friday, May 27 (with
    > which
    > > the Journal opens) corresponds with civil Thursday, May 26 p.m. and
    > > Friday, May 27 a.m.; his Saturday begins on civil Friday afternoon, ;
    > > so on. At Tahiti, as he explains,, he abandons this convention for civil
    > > time, reverting thereafter to ship time for the rest of the voyage."
    > >
    > > So, really, there's no excuse for any reader to misunderstand.
    > >
    > > ====================
    > >
    > > It opens up another question, however.
    > >
    > > Assume that mariners were indeed universally accustomed to using the
    > > nautical day in their logs. Considering that the new Nautical Almanac
    > > been especially prepared for their use, and indeed the Greenwich
    > > Observatory had been set up primarily for the benefit of nautical
    > > astronomy: then why were the astronomers so bloody-minded as to use the
    > > astronomical day, rather than the nautical day, for the Nautical Almanac
    > > tabulations? Conservatism, presumably. "That's the way we astronomers
    > > always done it."
    > >
    > > Once mariners' navigation started to depend on accurate numbers
    > > from an almanac, it seems that they then had to take account of a new
    > > time-scale, a day away from their normal accounting for time, with its
    > > additional likelihood of confusion and error. What a mess!
    > >
    > > I wonder what time-scale had been used in the tables provided to
    > > previously? The most essential would have been the daily tables of Sun
    > > declination. I have a modern reprint of Matthew Bourne's "A Regiment for
    > > the Sea", which, two centuries before the Nautical Almanac, provided Sun
    > > declination tables for each day at noon over a four-year cycle starting
    > > 1574: taken, I suppose, from Pedro Nunez. Presumably, the noons given in
    > > that table were for civil days, and corresponded to the last moment of
    > > same-numbered nautical day, and the first moment of the same-numbered
    > > astronomical day.
    > >
    > > The problem would become more critical when intermediate times, between
    > > noons, were interpolated into the predictions. The French "Connaissance
    > > Temps" which appeared much earlier than the Nautical Almanac, was
    > > mainly for astronomers and surveyors. Was its time-scale based on the
    > > astronomical day, I wonder?
    > >
    > > ======================
    > >
    > > The next question is- when did the noon-to-noon nautical day drop out of
    > > use? We know that the noon-to-noon astronomical day remained the basis
    > > nautical tables until 1925.
    > >
    > > The Admiralty may have directed that it should be dropped by the Royal
    > Navy
    > > in 1805, but it was certainly still alive-and-kicking in the Arctic
    > whaling
    > > fleet in 1813, and a reference quoted by Chuck Taylor states that it
    > > persisted into the 1820's in the East India Company..
    > >
    > > Trevor Kenchington says-
    > >
    > > >The Nautical Day, 24 hours early than the Astronomical Day, was long
    > > >established and of general application -- at least in the
    > > >English-speaking world. (Smyth, for example, treated it as an
    > > >established fact, without reservations or caveats.) I'm not sure when
    > > >entirely ended. I have a vague memory that it was still used in the
    > > >grain trade (under sail) in the 1930s, though I would be pushed to find
    > > >a reference to that.
    > >
    > > I wish only to question that last sentence. If the nautical day was
    > > being used so late as the 1930's, I would expect to see some references
    > > it in my collection of textbooks and tables dating from the mid 1800s,
    > > (from indexes only, not cover-to-cover scanning) I can find no such
    > > references. Not that such lack-of-evidence is in any way conclusive. It
    > > would be interesting to learn more, if only to avoid errors when
    > > old logs.
    > >
    > > George.
    > >
    > > ================================================================
    > > contact George Huxtable by email at george@huxtable.u-net.com, by phone
    > > 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    > > Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    > > ================================================================

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