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    Re: Slocum's lunars
    From: Frank Reed CT
    Date: 2003 Dec 12, 17:48 EST
    George Huxtable wrote:
    "I doubt if Frank Reed and I are going to agree much about whether Slocum
    took just one lunar on his circumnavigation, or whether he made it a common
    practice. Perhaps it may have been something between the two."

    Well, it's not a matter of huge importance anyway. Lunars are pretty obscure, no matter how you slice it. I have heard (verbally) two people refer to Slocum's voyage as "circum-navigation by lunar distances". That is, they believed (on no real basis, probably just anecdotally) that Slocum's *principal* method of determining longitude was lunars. I am highly sceptical of this belief and remain so.

    Slocum was a highly skilled small-boat navigator, but the methods he used were the ones that were used for centuries: noon Sun for latitude and dead reckoning for longitude. In any case, after this latest discussion, I am more convinced than before that Slocum used lunars probably only once and at best very rarely (twice?).

    George wrote:
    "Frank argues that Slocum's position, South of Rio, that was agreed with a
    ship was by dead-reckoning over the few days since leaving Rio, and not by
    lunar. I agree that it's a plausible explanation, and doesn't prove (or
    disprove) that a lunar was taken at that time."

    Oh come on. Slocum wrote of that experience: "The Spray, with her tin clock, had exactly the same reckoning. I was feeling at ease in my primitive method of navigation, but it startled me not a little to find my position by account verified by the ship's chronometer."

    Primitive method? Position by account? This is clearly NOT a reference to shooting lunars. It is not merely that he might have taken a lunar. He's saying that this was position "by account" --dead reckoning.

    And:
    "Frank appears to accept the lunar longitude between Juan Fernandez and
    Nukuhiva."

    Well, of course. I'm still open to speculation on his motives for shooting a lunar at this point. I wonder if he had begun to doubt his dead reckoning and after 46 long, long days at sea he needed re-assurance that he didn't have another 46 ahead of him.

    George wrote:
    "2. He towed a rotating log, which would indeed give him information about
    longitude; particularly on a mainly West-going passage, as this was. But
    for that, there was no input AT ALL required from a clock. It wasn't a
    speed-log, it was a distance-log. So why would Slocum refer to his clock,
    if that log was where his longitude was derived from?"

    You still need some basic clock when you do DR navigation. At minimum, you'll want to record your position at a regular time every day, let's say, 4pm, or once every four hours when closer to shore. A beat-up old clock would serve fine for this purpose as would a good sandglass. [off-topic but relevant to another thread: if you still haven't seen M&C --there's a whole lot of sandglass flipping in the movie, which I thought was an interesting theatrical touch]

    And:
    "3. I'm sure Frank and I would agree that that tin clock wasn't being used
    for any form of "longitude by chronometer"."

    Yes. I was curious what misinterpretations of the "tin clock" you've encountered from other navigators. When I mentioned lunars and Slocum to an old yachtsman who fancies himself knowledgeable in matters navigational, he started going on about getting my own tin clock. I couldn't quite fathom what he meant.

    "4. If it was just a matter of dead-reckoning from a log, why would Slocum
    refer to it as "the greatest science"?"

    Because DR is a science. It is NOT just a matter of reading the log. The science comes from knowing how to correct the position. There's another good example of Slocum's navigational "science" as he returns to the coast of Brazil towards the end of the voyage. He wrote:
       "On May 10 there was a great change in the condition of the sea; there could be no doubt of my longitude now, if any had before existed in my mind. Strange and long-forgotten current ripples pattered against the sloop's sides in grateful music; the tune arrested the car, and I sat quietly listening to it while the Spray kept on her course. By these current ripples I was assured that she was now off St. Roque and had struck the current which sweeps around that cape. "

    This method of getting the longitude by running into one of the several major currents off the east coasts of the world's continents is a classic method of navigation. It's just the sort of thing you don't need to pay attention to if you're navigating by lunars.

    And you wrote:
    "We have to remember that Slocum was writing a journal for the ordinary
    reader, not a log for the interest of Nav-l listmembers. Having described
    taking lunars once, in the Pacific, we shouldn't expect him to refer to
    each lunar observation thereafter in his text."

    I don't buy it. He spent paragraphs on his Pacific tale of a bad logarithm and not once does he mention elsewhere that he "verified the longitude by the trustworthy Moon" or some such?! He clearly and plainly refers to dead reckoning techniques in the book, but never manages to mention the Moon again?? Further, he clearly describes courses across long stretches of ocean that are constant latitude legs  --"running down the longitude". These constant latitude legs are exactly the sort of sailing that used to be commonplace on ships that could not be sure of their longitude via chronometer or lunars.

    And:
    "It is indeed a pity that his log no longer exists."

    Just to clarify, you're sure of that? This was one of the things I've been trying to find out.

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