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    Re: Sumner lines: was[NAV-L] Simple celestial navigation in 1897
    From: Lu Abel
    Date: 2006 Mar 14, 09:30 -0800

    With respect to Sun shots vs full Sumner line navigation, I understand
    that a poll of small boat voyagers (ie, your average offshore pleasure
    boat voyager) showed that the vast majority of them did ONLY Sun shots.
      Even in today's world of handheld calculators making sight reduction
    so simple, my understanding is that among offshore voyagers who still
    take celestial sights (vs depend solely on GPS) the majority of them
    still do only Sun sights.
    As we talk about position fixing, let's keep in mind the type of vessel
    and where she's operating.  If I'm the navigator on a high-speed
    transatlantic passenger steamship that's trying to keep a schedule
    year-round, I have a much greater need for constantly updated fixes than
    if I'm a pleasure boat following the trade winds across the Pacific or
    Atlantic at a more leisurely five or six knots.  For the latter type of
    folks, they're likely to be operating in much sunnier conditions and
    exact position is relatively unimportant except when approaching land
    (at which point I heave-to if the weather is bad enough that I can't get
    good positional information).
    This thread started with a discussion of the navigational log of the
    Charles W. Morgan.  I suspect the navigational requirements for whaler
    operating in the north Pacific would be pretty much the same as the
    transoceanic pleasure boat.
    Lu Abel
    Frank Reed wrote:
    > George H, you asked:
    > "If there were a few  diehard old-school mariners clinging to older methods,
    > then indeed position-line  navigation would not have become universal. Is that
    > all that he is  implying?"
    > No, nothing so wishy-washy! 
    > As late as the  1930s, a substantial minority (maybe 25%??) of navigators
    > were still using  straight, simple time sights and Noon Sun --no celestial lines
    > of position. At  some earlier date, that proportion crossed the 50% "tipping
    > point". I don't know  when that was (and it would be very tough to prove) but
    > I'm looking at 1900-1905  right now. That's sixty years after Sumner published.
    > I think there are plenty  of reasons for this including issues of plotting
    > and charting, vessel speed,  mathematical complexity, bias regarding algebraic
    > versus plotted solutions, and  also, perhaps, an intangible sense that a
    > problem already solved did not need  solved again (thou shalt not re-invent the
    > wheel --and yet we do).
    > And  you wrote:
    > "It seems to me that one of the conditions pushing mariners to  adopt Sumner
    > techniques was the climate. Mariners returning to anywhere in  Northern Europe
    > had to find one of the narrow approach channels around the  British Isles,
    > after an ocean passage. Our climate is such that the Sun may be  only fleetingly
    > visible for days at a time. If and when it appeared, the sextant  would be
    > brought out, whether it was noon or not. The chance was too precious to  be
    > missed. There might be weeks at a time when no noon sights were possible at  all."
    > Yes, I agree with that. Climatic differences might well explain  variable
    > rates of adoption of celestial lines of position in different parts of  the world.
    > By the way, somewhere in W.E. May's navigation history, there  is a comment
    > about pre-war navigators (meaning pre-1940s) in the merchant marine  dispensing
    > with position lines and "reverting to" time sights and Noon Sun. I  don't
    > have a copy handy, but I think I'm remembering the phrasing right. I don't  think
    > he's specific, but I assume he was talking about *British*  navigators.
    > -FER
    > 42.0N 87.7W, or 41.4N  72.1W.
    > www.HistoricalAtlas.com/lunars

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