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    Re: Use of AH for professional navigation
    From: Gary LaPook
    Date: 2011 Oct 6, 11:35 -0700
    Here is a link to a prior post that also reports the accuracy of some observations taken in the middle of the night at sea:

    http://www.fer3.com/arc/m2.aspx?i=114008&y=201009

    gl

    --- On Thu, 10/6/11, sjoquist.magnus@telia.com <sjoquist.magnus@telia.com> wrote:

    From: sjoquist.magnus@telia.com <sjoquist.magnus@telia.com>
    Subject: [NavList] Sv: Re: Sv: Re: Sv: Re: Use of AH for professional navigation
    To: NavList@fer3.com
    Date: Thursday, October 6, 2011, 3:14 AM

    I know practically nothing of air-navigation, but compared to a Cessna the accelerations of a cargoship it may be so that the ship is more steady. Whatever vibrations You have on a ship can be handled by standing with slightly bended knees and a fairly loose grip (fingertip) on the sextant (sitting is more difficult but probably there is no alternative on an aircraft). Rolling and pitching of the ship is not a serious problem if your sea-legs are fairly well trained. On a smaller boat, or on a very fast-going ship when the bow continiously hits the waves there would be a challenge, but I have never used sextants (for measuring vertical angles)  with AH's on such crafts.
     
    Night-observations can also, as You surely know, also be done without any AH at all provided Your night-vision is good and if You accept something around 10 NM-precision. Being 65 I cannot any longer brag with my night vision, but younger collegues take star- (and planet-) sights with very good results (no Moon around). With "very good" under nightconditions I here mean around 5 NM.
    Textbooks are OK, in general, but if the text does not match my own experiences I disregard the former.
     
    Correct me if I am wrong, but did not submarines occasionally take astro-sights ("periscopal")? Would be interesting to know what precision they had in their LOP's. Does not sound too easy imagining a dark windy night wintertime North Atlantic (read some of that in textbooks, though).
    /Magnus
    ----Ursprungligt meddelande----
    Från: garylapook@pacbell.net
    Datum: 2011-10-06 11:12
    Till: <NavList@fer3.com>
    Ärende: [NavList] Re: Sv: Re: Sv: Re: Use of AH for professional navigation

    Thanks for the input and we have discussed bubble sextants at  great length before and flight navigation too. I have half a dozen bubble sextants of various types. I am interested with your use of a bubble sextant at sea because most texts say, that due to the quick accelerations at sea, that the bubble sextant doesn't work too well. I have never tried using one of mine afloat. Greq Rudzinski might have some information about this usage.

    Here is a link to a group of us using our bubble sextants:

    http://www.fer3.com/arc/m2.aspx?i=111467&y=201001

    and more can be found in the archives:
    http://www.fer3.com/arc/sort2.aspx?y=201001su

    http://www.fer3.com/arc/m2.aspx?i=114097

    You may also find this of interest:

    http://www.fer3.com/arc/imgx/Bubble-sextants-Precision-Astrolabe.pdf




    I also have put up a website discussing flight navigation with bubble sextants:

    https://sites.google.com/site/fredienoonan/other-flight-navigation-information

    https://sites.google.com/site/fredienoonan/

    Welcome aboard.

    gl





    --- On Thu, 10/6/11, sjoquist.magnus@telia.com <sjoquist.magnus@telia.com> wrote:

    From: sjoquist.magnus@telia.com <sjoquist.magnus@telia.com>
    Subject: [NavList] Sv: Re: Sv: Re: Use of AH for professional navigation
    To: NavList@fer3.com
    Date: Thursday, October 6, 2011, 1:42 AM

    I am talking about artificial horizons for marine sextants, shipboard use.
    In teaching students how to astronav, I have also used buckets of water as reflecting device with very godd outcomes. The bucket horizon is of course useless on a moving vessel, but adds to the understanding of what corrections to apply and how the sextant works. It also gives the student the "YESSS"-feeling and adds to his/her interest for the Art of Navigation in general and the Art of Astro Navigation in particular.
     
    Re-reading some of present and previous discussions on AH's I have the impression that the core subject is marine surface navigation, even if air-navigation and military uses also in a wider perspective surely is relevant for the question about what is "horizontal". Training in areas without visible horizon is one very important step towards being an Astro Navigator.
    Sorry to all of You  if I have misunderstood the topic at hand.
    /Magnus

    ----Ursprungligt meddelande----
    Från: garylapook@pacbell.net
    Datum: 2011-10-06 09:53
    Till: <NavList@fer3.com>
    Ärende: [NavList] Re: Sv: Re: Use of AH for professional navigation

    Are you talking about the type of artificial horizons we have been discussing, a horizontal reflecting surface, or are you talking about artificial horizon sextants?

    gl

    --- On Wed, 10/5/11, sjoquist.magnus@telia.com <sjoquist.magnus@telia.com> wrote:

    From: sjoquist.magnus@telia.com <sjoquist.magnus@telia.com>
    Subject: [NavList] Sv: Re: Use of AH for professional navigation
    To: NavList@fer3.com
    Date: Wednesday, October 5, 2011, 11:46 PM

    Hi Gary  -
    Short answer is: Fine!
    Source: Own experience from the early mid -80's and early -90's (large commercial vessels =  quite stable platforms. Rolling yes, pitching yes, vibrations no!).
    Sub-source: Reports from former "students" (cadets Royal Swedish Navy) who have tried out some quite advanced instruments during their astro-training weeks onboard GLADAN and FALKEN (Navy Schooners).
     
    Longer answer: Assuming You "accept" a precision in position somewhat lesser (say around 5 NM uncertainty) than You would for daylight/twilight observations (say better than 2
    NM) under good conditions, You are happy to have it onboard, although it can be hard to persuade the shipowner to include it in his standard equipment on his vessels).
    Also: Takes a bit of training to get good sights, which is quite OK. Not a bad way to spend night-watches at sea.
     
    Best,
    Magnus
    ----Ursprungligt meddelande----
    Från: garylapook@pacbell.net
    Datum: 2011-10-06 08:17
    Till: <NavList@fer3.com>
    Ärende: [NavList] Re: Use of AH for professional navigation

    How do these artificial horizons work on shipboard?

    gl

    --- On Wed, 10/5/11, Magnus Sjoquist <sjoquist.magnus@telia.com> wrote:

    From: Magnus Sjoquist <sjoquist.magnus@telia.com>
    Subject: [NavList] Use of AH for professional navigation
    To: NavList@fer3.com
    Date: Wednesday, October 5, 2011, 10:43 PM

    Dear All -
    AH's are not only for desert/Arctic Navigation or for backyard training.
    They are also provide means for 24hour astronav on the High Seas.

    (Combined with dark-vision telescope we are talking about costs around 10.000 USD or more which normally is out of range for private (or students) budgets)).

    Best!
    Magnus Sjoquist
    (Thanking You All for very interesting reading on this and other matters).
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