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    Re: Bubble sextant intervention needed.
    From: Paul Dolkas
    Date: 2012 Oct 20, 11:10 -0700



    Perhaps you’re missing my point – a sextant needs to be able to be out in the sun  for a good 10-15 minutes, or else you’d never be able to take a few sun shots (esp. in rough conditions). And I’ve never had the misfortune of having the silver scale jump out of the frame –  perhaps my Davis wannabe is built better than I thought it was!


    Since some sextants are painted white, I couldn’t understand why they all aren’t done that way – certainly the plastic ones could benefit from this, since they (mine anyway) warp significantly in the time it takes to get a few good shots. I was taught you need to zero them out just before a shot, and then check the index error just after you finish. I’ve always had at least the better part of an arc minute error increase between the two checks in warm conditions. (That’s what I get for buying plastic!)


    In any case, I like Ronald’s answer about reflections in a navigator’s dome.  I’ll just have to make sure I have a good 1/8” bubble to start with on a warm day – smaller ones can shrink too much, even in the shade.





    From: navlist-bounce@fer3.com [mailto:navlist-bounce@fer3.com] On Behalf Of Brad Morris
    Sent: Friday, October 19, 2012 8:57 AM
    To: NavList@fer3.com
    Subject: [NavList] Re: Bubble sextant intervention needed.


    Agreed Geoffrey.  The navigator is urged to permit the sextant to reach thermal equilibrium prior to observations, but I never recall seeing advice urging the navigator to do that by leaving the device out in the sun!

    Best Regards

    On Oct 19, 2012 11:51 AM, "Geoffrey Kolbe" <geoffreykolbe@compuserve.com> wrote:

    At 07:23 19/10/2012, you wrote:


    Well I'm not, really - but I was always taught that you need to leave a
    sextant out to equilibrate with the outside temp before taking a sighting.

    With respect Paul, I don't think you were ever taught to leave a sextant out in the sun! The great danger of that is that the silver scale jumps out of the frame and renders the sextant instantly and totally useless. X;{



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