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    Re: When did "time sights" fade away?
    From: George Brandenburg
    Date: 2011 Jul 13, 11:56 -0700

    For some of us they never have faded away! Since my primary interest is how ships navigated in the late eighteenth and early nineteenth centuries, I'm quite content thinking in terms of noon, time, and lunar sights. Although I think LOPs are great for visualization, I'll stick with what I learned from Frank down at Mystic!

    We have started a new "helm program" on the Friendship at the Salem National Maritime Historic Site. This is a 20 minute demonstration for ship visitors showing them how the ship navigated its way across the ocean long before GPS. They learn about steering on a compass heading, dead reckoning (with a log line and traverse board), lead line sounding near shore, and finally a very brief intro to celestial navigation (old style).

    In the latter the visitors learn how easy it is to measure latitude by a noontime sun sight, and then they get to do an actual sun sight with a Davis sextant (even though it isn't usually noon and we don't have a horizon). As for longitude we just say it was a much more difficult measurement that involved measuring time via the moon's position (Salem's ships couldn't afford new-fangled chronometers).

    The finale is a globe showing the Friendship's maiden voyage from Salem to Batavia (Jakarta) in 1797-8. The plot of the logged positions has long stretches of constant latitude sailing, and lunar longitude measurements at strategic course changes. For example there is a long stretch where the ship sailed from the middle of the S Atlantic eastward at a constant latitude of about 38 deg S until it had cleared the Cape of Good Hope and reached the middle of the Indian Ocean. There are lunar longitude points both at the beginning and end of this stretch.

    The majority of the visitors who attend these demonstration really seem to get it. And what is encouraging for me is that the staff rangers are able and willing to explain and demonstrate cel nav at this level, instead of leaving it for their resident expert (yours truly) to explain.

    George B
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