# Naval custom of thirteen months. **URL:** \ **Category:** Factual Questions\ **Created:** [April 21, 2004, 6:11am UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181 "2004-04-21T06:11:15Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Willmore](https://avatars.discourse-cdn.com/v4/letter/w/ad7895/32.png) [@Willmore](https://boards.straightdope.com/u/Willmore)\ **Post date:** [April 21, 2004, 6:11am UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/1 "2004-04-21T06:11:15Z")
I was reading O’brian’s “H.M.S. Surprise”, and in one of his mid-sentence mentions, that never explain themselves he said “They talked about … the naval custom of having thirteen months in a year …” I did some minor research on it, and came out striking-out on all fronts. So can someone enlighten me on this obscure custom ? ---
**Author:** ![Mojo\_the\_Monkey](https://avatars.discourse-cdn.com/v4/letter/m/eada6e/32.png) [@Mojo\_the\_Monkey](https://boards.straightdope.com/u/Mojo_the_Monkey)\ **Post date:** [April 21, 2004, 2:53pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/2 "2004-04-21T14:53:41Z")
> [@Willmore](#): > > I was reading O’brian’s “H.M.S. Surprise”, and in one of his mid-sentence mentions, that never explain themselves he said “They talked about … the naval custom of having thirteen months in a year …” > > I did some minor research on it, and came out striking-out on all fronts. So can someone enlighten me on this obscure custom ? I’ve never heard of this before, but if you divide 365 by 13, you get something like 28.07, so perhaps it’s just a handy way to have months of equal length, all filled out with full weeks? With this system, the first is always on a Sunday and the 28th is always on a Saturday. That’s got to make vital ship’s functions like timekeeping and recordkeeping much easier… ---
**Author:** ![Paul\_in\_Qatar](https://avatars.discourse-cdn.com/v4/letter/p/ccd318/32.png) [@Paul\_in\_Qatar](https://boards.straightdope.com/u/Paul_in_Qatar)\ **Post date:** [April 21, 2004, 2:55pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/3 "2004-04-21T14:55:56Z")
News to me, I hope to learn more. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [April 21, 2004, 3:24pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/4 "2004-04-21T15:24:17Z")
POB also mentions the Naval day beginning at noon. What’s up with this besides the sun? ---
**Author:** ![APB](https://avatars.discourse-cdn.com/v4/letter/a/8e8cbc/32.png) [@APB](https://boards.straightdope.com/u/APB)\ **Post date:** [April 21, 2004, 3:36pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/5 "2004-04-21T15:36:14Z")
Because at that time O’Brian’s novel is set, the Royal Navy paid sailors’ salaries by lunar month. (I assume that this was not for any real administrative reason but because ordinary sailors on long voyages were more likely to reckon the passage of time by the phases of the moon and so would be reassured that they were receiving the correct amount.) ---
**Author:** ![muldoonthief](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/muldoonthief/32/3188_2.png) [@muldoonthief](https://boards.straightdope.com/u/muldoonthief)\ **Post date:** [April 21, 2004, 3:51pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/6 "2004-04-21T15:51:41Z")
> [@carnivorousplant](#): > > POB also mentions the Naval day beginning at noon. > What’s up with this besides the sun? Since the ship was moving, finding the difference between local time and GMT was necessary to determine location, and had to be done daily. Noon was the best time to do it, since midnight made shooting the sun rather difficult. Since it was such a big ceremony each day (POB describes all the officers and middies doing it in several books), it made sense to reset the ship clock (i.e. the glass) at the same time. This is somewhat related to what has to be the funniest running gag in the Aubrey/Maturin series: Some non-nautical passenger: “Why is the shortened watch called the dog watch?” Maturin: “Because it is cur-_tailed_!” ---
**Author:** ![pravnik](https://avatars.discourse-cdn.com/v4/letter/p/8edcca/32.png) [@pravnik](https://boards.straightdope.com/u/pravnik)\ **Post date:** [April 21, 2004, 4:01pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/7 "2004-04-21T16:01:14Z")
Lousy Smarch weather! ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [April 21, 2004, 4:14pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/8 "2004-04-21T16:14:20Z")
While I have you here… WTH is an “instant”? as in “Fell in with a privater or the 12th instant…” ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [April 21, 2004, 4:30pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/9 "2004-04-21T16:30:23Z")
“the 12th instant” or “instt.” means “the 12th of the current month.” ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [April 21, 2004, 4:39pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/10 "2004-04-21T16:39:53Z")
Similarly – the 12th ultimo (ult.) = the 12th of the previous month the 12th proximo (prox.) = the 12th of the upcoming month ---
**Author:** ![Mr.Moto](https://avatars.discourse-cdn.com/v4/letter/m/9de0a6/32.png) [@Mr.Moto](https://boards.straightdope.com/u/Mr.Moto)\ **Post date:** [April 21, 2004, 5:28pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/11 "2004-04-21T17:28:16Z")
Log keeping in the modern Navy is much simpler than this. We still “dog the watch,” though. This is usually done to split the 1600 to 2000 watch into two halves. This allows sailors to eat dinner either before or after watch, and also puts an odd number of watches into a day. With an even number of watch sections, you now have a watch rotation, so the same section isn’t stuck working in the middle of the night all of the time. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [April 21, 2004, 5:39pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/12 "2004-04-21T17:39:13Z")
> [@muldoonthief](#): > > Since the ship was moving, finding the difference between local time and GMT was necessary to determine location, and had to be done daily. Noon was the best time to do it, since midnight made shooting the sun rather difficult. Since it was such a big ceremony each day (POB describes all the officers and middies doing it in several books), it made sense to reset the ship clock (i.e. the glass) at the same time. No. The noon sight cannot determine time with the accuracy needed for celestial navigation. The noon sight was used only to determine latitude and it was only with the advent of the chronometer that longitude could be reliably determined at sea by celestial observations. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [April 21, 2004, 6:29pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/13 "2004-04-21T18:29:13Z")
> [@sailor](#): > > advent of the chronometer that longitude could be reliably determined at sea by celestial observations. Aubrey had chronometers, one provided by the admiralty, and as he became wealthy two expensive, more accurate ones of his own. I presume the naval day began at noon when there were no chronometers? ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [April 21, 2004, 8:27pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/14 "2004-04-21T20:27:55Z")
I am not sure there ever was any such concept as the “naval day”. As far as timekeeping is concerned the day starts at midnight just like on land. I suppose the closest concept would be that local apparent noon marked the end of the forenoon watch and also the day’s run which AFAIK was always reckoned from noon to noon. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [April 21, 2004, 8:41pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/15 "2004-04-21T20:41:13Z")
From _Desolation Island_ “… the Leopard fixed her position by the sun; and every day the sun climbed higher in the south. As the crucial moment approached, the moment when it should cross the meridian, her captain, her master, all the watch-keeping officers, and all the young gentlemen would train their instruments, hold their breath, bring the sun’s limb to the horizon, and record the result. The master would report, ‘Noon, sir’, to the officer of the watch; the officer of the watch would cross the quarterdeck to the Captain, take off his hat, and say, ‘Noon, sir, if you please’, and the Captain, who knew it perfectly well from his own sextant, even if he had not heard the master’s voice a few yards from him, would say, ‘Make it twelve, Mr Babbington’ (or Grant or Turnbull, as the case might be) thus setting the boundary between one naval day and the next.” ---
**Author:** ![johncole](https://avatars.discourse-cdn.com/v4/letter/j/5f9b8f/32.png) [@johncole](https://boards.straightdope.com/u/johncole)\ **Post date:** [April 21, 2004, 8:53pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/16 "2004-04-21T20:53:47Z")
> [@sailor](#): > > I am not sure there ever was any such concept as the “naval day”. As far as timekeeping is concerned the day starts at midnight just like on land. I suppose the closest concept would be that local apparent noon marked the end of the forenoon watch and also the day’s run which AFAIK was always reckoned from noon to noon. According to [this link](http://www.nmm.ac.uk/site/request/setTemplate:singlecontent/contentTypeA/conWebDoc/contentId/9098/navId/005002007004) from the UK National Maritime Museum: > [@](#): > > The mariner’s day also began at a different time. Until an Admiralty order of 11 October 1805, the nautical day began and ended at midday and was 12 hours ahead of the civil day. Midday was of particular importance because this was the time when the major observations were recorded for position, course and distance run in the preceding 24 hours. To add to the difficulty of dating, when a ship entered port the civil day took precedence. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [April 21, 2004, 9:24pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/17 "2004-04-21T21:24:05Z")
The point is that this is not a clearly defined concept. The same way you can say my day starts when I get out of bed in the morning. Yes, the day’s run was reckoned from noon to noon and noon marked the end of the forenoon watch so, in that sense you can say it was the “beginning of the day” in the same way that my getting out of bed marks the beginning of my day. It is an important mark in the day. You can say “fiscal year 2003 starts April 1 2003 and ends March 31 2004” and then “Fiscal Year 2003” is clearly defined. Now, I have _never_ heard it mentioned that Monday, July 23, on a ship started at anything else than midnight. Astronomers reckon Julian dates from noon to noon and they are clearly defined as such but, AFAIK, the civil day on a ship, (e.g. Monday the 13th of June) never started at noon. I have never seen a cite saying “at noon day X finished and day Y began”. I would also be very careful with using movies or novels as reliable sources. The noon sight’s main purpose was to observe the sun’s height over the horizon in order to determine the latitude of the ship. The scene described in that paragraph may be very picturesque but does not sound realistic to me as there is not even a mention of the observed height or the ship’s latitude which was of more importance than the formal reckoning of noon time. I would only expect such a number of people observing the sun in a training ship. In a regular ship probably there were not more than two or three people at the most who were capable of doing celestial navigation. In merchantmen it was very often only the captain. And it was not like everybody had sextants either. They were terribly expensive. The sextant was invented around 1750 but it took decades to become widespread and navigators continued to use their backstaffs for a long time. Ships sailing in company talked daily to exchange observations. Ships meeting in the high seas would also exchange information about their reckoned positions. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [April 21, 2004, 9:28pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/18 "2004-04-21T21:28:28Z")
> [@sailor](#): > > I would also be very careful with using …novels as reliable sources. Sir, you speak of Patrick O’Brian. My Second shall call upon you in the morning. 🙂 ---
**Author:** ![Mr.Moto](https://avatars.discourse-cdn.com/v4/letter/m/9de0a6/32.png) [@Mr.Moto](https://boards.straightdope.com/u/Mr.Moto)\ **Post date:** [April 21, 2004, 10:12pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/19 "2004-04-21T22:12:47Z")
It is still custom in the U.S. Navy to mark noon by asking the captain’s permission to strike eight bells on time. This, of course, marks the start of the afternoon watch. ---
**Author:** ![johncole](https://avatars.discourse-cdn.com/v4/letter/j/5f9b8f/32.png) [@johncole](https://boards.straightdope.com/u/johncole)\ **Post date:** [April 21, 2004, 10:26pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/20 "2004-04-21T22:26:29Z")
> [@sailor](#): > > The point is that this is not a clearly defined concept. It was very clearly defined in HM ships at sea until the Admiralty order referenced in my previous post changed the rules. An [additional link](http://www.aandc.org/research/nautical_time_and_date.html) from the Archives and Collection Society of Canada, referencing contemporary documents. > [@](#): > > Till 1805 logs were kept in nautical time; that is to say when they were written up at mid-day, **that day’s entry consisted of the proceedings for P.M. of the day before and A.M. of that day**. [2] The change was ordered by Admiralty Circular of 11th October 1805 which ordered that “the calendar or civil day is to be made use of, beginning at midnight.” > [@](#): > > [2] Mariners reckon time in the astronomical manner, beginning at noon and counting from thence 24 hours to the next noon. The first 12 hours, from noon to mid-night, they mark with P.M., signifying after mid-day; and the second 12 hours, from mid-night to noon, they mark with A.M., signifying after mid-night; and end their day’s work on the noon of the nominal day. Hence their ship account is 12 hours earlier than the civil account of time > [@](#): > > Thus that day’s account which is marked Sunday the 9th of October, began on Saturday noon, and ends on Sunday noon [Next page](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181.md?page=2)