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    Re: Ex RNZAF navigator keen to learn marine sextant ways
    From: Howard G
    Date: 2021 Dec 3, 15:15 -0800

    Hi David and the Other Contributors - great to be aboard with such a wealth of knowledge not yet lost.

    I used 2 different sextants - as an ab initio nav on Bristol Freighters - I used the RAF Mk IX bubble sextant up through an astrodome exactly as per navs of WWII - exactly. - worked fine day or night. Bubble worked well - fixing was accurate - Freighter chugged along at 150 kts so 3 star fix took 10 minutes - max altitude was 10,000 ft so often in cloud and rough - but we got pretty good at sites.

    Then posted to P3B Orions - a very different aircraft - pressurissed - up to 30,000 -  Kollsman periscopic - excellent sextant - pendulous sextant up through pressure hull - lighted false horizon I believe - very narrow field though - it was difficult to find a star if you didn't know where it was - beauty was you had a true north compass and the mount had bearings marked out so you could set the LHA/SHA of the star you were shooting - wind in the altitude - and there it was - for any of the stars you wanted to shoot.

    Problem was if you then encountered cloud - and had to re-compute for a different star - up at 30,000 the atmosphere was crystal clear and I knew the stars by sight.

    Early problem was then it took 10 minutes to calculate a new 3 star fix from tables - and you were travelling at 6 nms per minute - 10 minutes = 60 nms - things change quickly.

    Solved that problem - bought a Scientific TI calculator - 1st on market in 1978 - magnetic card reader - put all my tables into mag cards - could then select star, time etc and voila - had 3 star fix in about 1 minute - didn't matter if cloud covering part of sky could just look for star in clear area and claculate in less than a minute. Changed the game.

    But all those cards and workings and notes long gone - got to start again.

    Thanks for info on U Boats  - interesting stuff - WW II buff aero, marine - very interesting. 

    Will read your comments more thoroughly and come back with more questions no doubt as I brush up on knowledge.

    Thanks again everyone for comments - looking forward to partaking in forum.

    Regards Howard

       
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