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    Re: New compact backup CELNAV system
    From: Gary LaPook
    Date: 2009 Apr 10, 23:22 +0200

    I've been traveling for a while and haven't been able to get back to
    this (Amsterdam, Athens, Rhodes, Crete, Istanbul, Cairo, Rome and now in
    Ken, maybe we see the word "backup" slightly differently. My suggested
    method was meant for those who already know celnav, it was not meant to
    be "Celestial Navigation For Dummies" a self teaching book. I meant it
    for a navigator who was considering whether it was worth the bother
    anymore to carry the sextant, requisite tables (H.O. 249, H.O. 229,
    etc.) and to remember to get a new Nautical Almanac every year (may be
    difficult where you are) or just give up celnav and buy an additional
    GPS to use as a backup. The flat Bygrave allows a navigator to decide,
    that without having to allow shelf space for books he will probably
    never use and not having to remember to get any almanac except once in
    every ten years (that can be downloaded for free from the Government web
    site,)  he will just go ahead and keep that old sextant and these couple
    of pages and forgo spending money on that additional GPS unit.
    Especially since an additional GPS doesn't offer complete redundancy
    since the whole system could be made unavailable by some military action
    or by our government shutting it down at the most inopportune moment in
    order to deal with an enemy attack or terrorist plot. Celnav, on the
    contrary, does supply complete redundancy and is self contained needing
    nothing from the outside except a hole in the clouds.
    Or the flat Bygrave could be used as the primary sight reduction method
    for a sailor who practices celnav regularly but appreciates the
    reduction in storage space and hassles of obtaining Nautical Almanacs
    each year. The accuracy of this method is perfectly adequate for normal
    celnav and is about the same as that obtained with H.O 249 a popular
    method used by small boat navigators. Call it a "compact" sight
    reduction method instead of a "backup."
    For anybody looking for a compact method and who doesn't like the flat
    Bygrave I would recommend getting a copy of  Weems Line of Position Book
    or Dresionstok (each are easier than Ageton) to replace their H.O 229,
    H.O. 214 or H.O 249 and then to also use the long term almanac from H.O
    249 that I included with the flat Bygrave.
    As you will see my other post today, I have nothing against crossing a
    morning sun line with an afternoon sun line to provide a running fix,
    use any method you like to accomplish this.
    Ken Gebhart wrote:Gary,
    > The interest in your Bygrave project has been great and well
    > deserved.  But when talking about "backup" systems, I think about one
    > who is ill versed in CN, and just wants to make a safe landfall
    > without his failed GPS.  In this situation, I feel that using simple
    > noon sight procedures supplemented by sunrise/sunset longitudes, and
    > polaris Lats would be fine.  All that would be needed would be the
    > Nautical Almanac (for the Sunrise/ Sunset things) and would have the
    > included SR Tables for intermediate sights.  One might not prefer
    > these NA SR tables, but they DO work, and in a backup situation, why
    > be choosey?
    > Ken
    > On Mar 17, 2009, at 6:26 PM, glapook@PACBELL.NET wrote:
    >> I am real happy that I kicked off this topic and am impressed by the
    >> level of interest shown in using this simple to produce modification
    >> of the Bygrave for a backup celnav system. I am also impressed by the
    >> improved scales created by the other members on this list. A while ago
    >> I contacted Ken Gephart at Celestaire to get his opinion on whether he
    >> thought there would be any interest in a commercially produced version
    >> but he didn't think there would be. He thought that a simpler system
    >> would be better considering the lack of celestial training of your
    >> everyday sailor. I started this discussion stating that it was meant
    >> for those knowledgeable in CELNAV, the virtue of this system being its
    >> compact size and its low cost. He said that if they already had the
    >> Nautical Almanac they had the reduction tables already published in
    >> the N.A. (I, for one, really dislike those tables, your mileage may
    >> vary.) Work out an example with the N.A tables and compare the work
    >> with the came computation with the Bygrave and I think you will agree
    >> the Bygrave is easier to use. Those same non celnav sailors wouldn't
    >> be expected to buy an N.A. every year either so another advantage of
    >> this system is the long term almanac.
    >> So Ken, any more thoughts about this considering the great interest
    >> shown on this list?
    >> gl
    >> On Mar 17, 1:09 pm,  wrote:
    >>> I am another long time lurker, who got all excited about Gary
    >>> LaPook's flat Bygrave scales, and also got cracking on my own
    >>> version of scales. Unfortunately it took me a while to complete
    >>> due to distractions like family and job. So Dave beat me to it by
    >>> a month or so.
    >>> In any case I decided to publish my version of scales as well. Not
    >>> because they are better than Dave's, but because they are written
    >>> in Postscript, and can be easily customized by each individual
    >>> user. It's easy to change width of scales to the size of your
    >>> sheet or cylinder, number of lines, font size, frequency and
    >>> thickness of tickmarks etc.
    >>> The files cot.ps and cos.ps can be edited with text editor like
    >>> notepad, and then converted to PDF using free Ghostview tool. To
    >>> do that you also need to install Ghostscript. Here are links to
    >>> download page.
    >>> http://pages.cs.wisc.edu/~ghost/doc/GPL/gpl863.htmhttp://
    >>> pages.cs.wisc.edu/~ghost/gsview/get49.htm
    >>> You could even easily define other scales using this template e.g.
    >>> sec()/csc() for Ageton method like Andrew suggested in one of the
    >>> previous posts. Though this would require to write up the function
    >>> in Postscript stack based form using just (sin, cos, and atan) as
    >>> these are only available trigonometric functions in postscript. I
    >>> would be glad to help, if somebody decides to do that.
    >>> Note that common procedures for drawing the scale are in scale.inc
    >>> file and it must be in the current directory when opening .ps
    >>> files with ghostview.
    >>> And I must also repeat Gary's warning, when printing PDF files
    >>> make sure to set Page Scaling to None. I wasted few transparent
    >>> sheets before figuring that out.
    >>> Martin
    >>>  cos.ps
    >>> 1KViewDownload
    >>>  cot.ps
    >>> 2KViewDownload
    >>>  scale.inc
    >>> 2KViewDownload
    >>>  cos.pdf
    >>> 23KViewDownload
    >>>  cot.pdf
    >>> 85KViewDownload
    > >
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