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    Re: long lost lunars
    From: Frank Reed CT
    Date: 2003 Dec 11, 19:19 EST
    I wrote earlier:
    "Now how about Slocum? Everyone mentions him when they talk about lunars, but reading "Sailing Alone Around the World", it seems that he barely used the technique. Is there other evidence (his log book) that he practiced lunars during his circum-navigation?"

    And George Huxtable replied:
    "And I think somewhere recently (but I can't locate it now) Frank implied
    that Slocum used lunars only once in his circumnavigation."

    Yes, I did say that, and that's what I'm getting at. There is the famous --and famously quotable-- section in SAATW where he tells of one instance where he was very bored on a long passage and amused himself by shooting a lunar. But his primary method of determining longitude was dead reckoning. My question is simply whether anyone knows if there is any OTHER evidence that he used lunars on his circum-navigation.

    George worries:
    "All this is a vile calumny on my favourite voyager! "

    Nah. He's the Mark Twain of the ocean.

    And:
    "I think Frank should re-read his Slocum"

    Tsk-tsk. George, they passed out SAATW with bottles of milk when I was little. I grew up in the smaller, quainter town next to Mystic: it's Noank, Connecticut, and when I was in grade school I used to play in a small backyard where a reproduction of Spray was being built. My friend's family finished their version of the boat and sailed off into the distance when I was ten. They returned from their circum-navigation when I was fifteen. Even the original "Spray" spent some time in Noank before Slocum unbuilt it and rebuilt it (if you dig, you'll find the name of "Noank" in the appendix of he book). I re-read SAATW this past summer mostly because several people suggested that Slocum circum-navigated the globe "using lunars". I'm fairly confident that that wasn't the case. So far, there is evidence that he used lunars *once*. I would be pleased to be hear evidence (*real* evidence) that he used lunars on a regular basis on Spray.

    And:
    "as I have just done: for the nth time (and a pleasure each time)."

    Yes, it's great fun to read. Have you read "Falcon on the Baltic" which I linked in that earlier message? Also a pleasure.

    George added:
    "Slocum mentions, early on, that although he owns a chronometer it would
    cost $15 to get it cleaned, so he decided to leave it behind. At Yarmouth
    he purchased his famous tin clock, the price of which was a dollar and a
    half "but on account of the face being smashed the merchant let me have it
    for a dollar".

    All of this is common knowledge, but what does it have to do with lunars? He needed an ordinary clock for dead reckoning --not necessarily for lunars.

    And wrote:
    "South of Rio, "Spray" exchanged positions with a steamship, and, with her
    tin clock, had exactly the same reckoning."

    Yes, Slocum's dead reckoning was dead on.

    And on to the ONE event of shooting lunars in SAATW:
    "43 days out from Juan Fernandez he says- "If I doubted my reckoning after a
    long time at sea I verified it by reading the clock aloft made by the Great
    Architect, and it was right."
    Nearing Nukahiva (Marquesas), he obtained a lunar longitude that was within
    5 miles of his dead reckoning, and when sighting it found that his
    longitude was halfway between those two reckonings. He said "even expert
    lunarians are acknowledged as doing clever work when they average within 8
    miles of the truth." Clever work indeed. But this was after discovering an
    error in a logarithmic table that otherwise would have put him many
    hundreds of miles out."

    This was on a long, long, dull passage from Isla Juan Fernandez. He had time to kill and he decided to dust off his knowledge of lunars. He speaks of "long wrestling with lunar tables", but a navigator who did them regularly could do the tables work in twenty minutes easily. It is not uncommon for beginners and calculators who are out of practice to blame their tables when they can't get things right the first time. To me, the fact that he says he has "discovered" an error in his logarithm tables is evidence that he did lunars rarely (maybe just this once on the whole circum-navigation). He didn't need to do them. Slocum himself wrote: "I hope I am making it clear that I do not lay claim to cleverness or to slavish calculations in my reckonings. I think I have already stated that I kept my longitude, at least, mostly by intuition A rotator log always towed astern, but so much has to be allowed for currents and for drift, which the log never shows, that it is only an approximation." [incidentally, you quoted this same passage and said that he wrote it when he was crossing the Indian Ocean, but wasn't this from the same section where he was describing his one lunar sight in the eastern Pacific? ]

    On a voyage like this where you can pick your path across the sea and choose the timing for convenience, dead reckoning is quite sufficient for crossing oceans. He had no schedule to keep, no cargo to deliver. There was no money on the line. Slocum write of constant latitude legs and "runnning down the longitude" in a couple of places. These are the standard approaches of dead reckoning longitude navigation. You get latitude by the Sun every day at noon and longitude by distance run corrected for set and drift. By running down the longitude, you have little risk of going wrong.

    And George quoted:
    "But the greatest science was in reckoning the longitude. My tin clock and only timepiece had by this time lost its minute-hand, but after I boiled her she told the hours, and that was near enough on a long stretch."

    He's talking about dead reckoning. If you want to know how far you've travelled in four hours, you need to know what four hours is. The minute doesn't matter much when you're doing five knots.

    Stating the essence of his opinion, George writes:
    "These passages are written in such a way as to imply that the lunar observations were routine matters that were kept up at regular intervals. How, otherwise, could he have had lat and long readily at hand to exchange with that steamship?"

    I don't agree with you at all on this. I think your use of the word "imply" is critical here. You're reading between the lines, and I find the evidence (from the book itself) weak at best that Slocum used lunars more than once on his circum-navigation.

    George added:
    "In taking a lunar, the angle changes so slowly that precise timing is
    unnecessary. The requirement for extreme precision is in the angle, not in
    the time. A clock with an hour hand only could probably be estimated to the
    nearest minute or two, which was close enough to relate a morning
    time-sight to a measured lunar distance."

    Look, I have no doubt that Slocum could have done lots of lunars if he had had reason to do so. But if he had reason, he probably would have paid up to get his old chronometer refurbished... Just a few days ago, we discussed the issue of doing time sights separately from the lunar sight. This is a trivial matter, and any clock that ticks would be up to the task. You do your time sight, you start your watch precisely when the time sight is taken, then you do your lunar --the sooner the better but it's not critical if you have to wait a while. You add the time on the watch from the lunar to the calculated local mean time from the time sight, and then compare with the Greenwich time deduced from the lunar. A person who can count seconds competently (and still handle a sextant without losing count) could do this. So the question of the tin clock is not relevant to lunars. It would neither have helped nor hindered the practice of lunars on "Spray".

    And you wrote:
    "And it could give a rough measure of time (and therefore longitude) for a few days thereafter. Even if it had been boiled. So Slocum's claim isn't impossible."

    I don't think Slocum *ever* claimed that he kept longitude on the tin clock, but yes, some people have misread SAATW thinking that's what he meant.

    "Even professional navigators have taken his tin clock joke seriously."

    What do they think he meant? That he was using it as a chronometer?!

    And you wrote:
    "In the hands of skilful observers and patient computers the Lunar Method is reliable within a quarter of a degree longitude, which would be the distance of a high landfall..."

    The accuracy of the lunars method is not at issue. As I have described in a number of posts, I've used it with great success and understand its strengths (and limitations) in some detail. What I'm interested in with respect to SAATW is something that strikes me as a bit of an urban legend. I don't think Slocum "practiced" lunars on his circum-navigation any more than anyone else did in that era. He used them once to entertain himself on a long passage approaching the Marquesas. That much is not in doubt. Did he shoot any others during his circum-navigation? I doubt it. He frequently describes dead reckoning navigation. I think that's how got longitude on his voyage.

    And you concluded:
    "As for me, I think that Joshua Slocum was a gifted teller of tales, and
    don't think we need to accept every word as gospel truth."

    Good for you, and I agree. Now... is there *evidence* of Slocum's navigation methods on "Spray" that would tell us how he sailed? Does anyone know what became of his log book from that voyage? I've seen a number of whaling ship log books from the 1840s and they used lunars once or twice and they note it in the log when it's done.

    Frank E. Reed
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois



       
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