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    Re: Averaging
    From: Joel Jacobs
    Date: 2004 Oct 7, 14:58 +0000



    Thanks for mentioning the averaging mechanism of bubble sextants for aircraft. Our resident expert on this type instrument, and instruments in general, is Ken Gebhardt of Celestaire, and some others on this list all of whom I will allow to correct me. I'm operating off a laptop without most of my files, but I would like to make the following comments.


    1. Shooting sights from high speed surface craft are subject to the same problems as those taken from an aircraft with the magnitude of the error being a function of ship's heading. I think George H has submitted some details earlier.


    2. The type of forces a small boat navigator is subjected to in heavy going is just as extreme as in an aircarft.


    3. The USN introduced a sextant years ago for surface navigation that dropp BB shot in an attempt to average sights. It was unsuccessful.


    4. I have maintaind that a odd number of sights should be taken with the results averaged when shooting from smaller size vessels. This is less important as tonnage increase. I also reccommend shooting from the crests of waves and never from the troughs.




    Some people have asked to see pictures of the damages incurred where we used to live in Fort Pierce, FL


    This link has a portfolio of some of them.



    Even though off topic, these comments explain them:


    Pictures of what we were most interested in. Note the two white sailboats next to one another. Then look at the newspaper picture taken from a helicopter. The boat with the clipper bow was blown into our slip.  It is a CSY 44. All three were later sunk. We now are in a 50 foot MY that I hauled before the storm. The boats in the slips had extensive damage from the boats that were blown behind them. The large dark objects are remnants of the floating docks which are all gone, as is the boats that were moored to them. The vacant water with just a few pilings remaining is where four floating docks were. They had about 100 boats secured to them of which 70 were destroyed. It is reported they were secure at 1 AM which is about when the eye hit us. The boats which have fallen off their skids are in a boat yard just across the way from us. The street scene shows we were alone when we first ventured out on Saturday morning. It stayed that way for two days. ! ;


    On 26 SEP Hurricane Jeanne hit the same area a second blow (no pun). We had moved South to a Hurricane Hole in Jupiter in anticipation of this on 23 SEP, and sustained some superficial damage, nothing of consequence.

    Sea Ya,


    Joel Jacobs


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    -------------- Original message from Michael Dorl : --------------

    > >
    > >(However, I imagine that this recommendation has to be modified
    > >for a navigator of a strategic bomber flying at 600 knots.
    > >I don't know much about the aerial navigation, but I suppose
    > >it had to be done by cell nav before GPS era, and if you are over an
    > >ocean).
    > As I understand it, there's an added problem in a plane because the plane
    > tends to roll causing the gravity
    > vector to oscillate. Many of the WW2 era aviation sextants have mechanical
    > averaging devices to compensate
    > for this; mine has a 1 minute averager. One minute at 300 miles per hour =
    > 5 miles.
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