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  1. #11
    Join Date
    Nov 2009
    Location
    currently in Pto Montt, Chile
    Posts
    217

    Default Re: Length of day at high latitudes?

    More than a few red herrings being chucked into the mix here.... oblate spheriods and sidereal days included.

    Square rigger running her easting down in 45*S at 15 knots..... 360 miles a ( 24h) day.

    If she was at the equator that would see her covering 6* of longitude a day

    At 45*S that would be 6*/.7 = 8.5*.

    So they would be advancing the clocks 30 minutes every night with a 1 hour advance about once a week.

  2. #12
    Join Date
    Jul 2002
    Location
    Farnham, Surrey
    Posts
    20,746

    Default Re: Length of day at high latitudes?

    Quote Originally Posted by Frank Holden View Post
    'Noon' has a different meaning to sailors... or at least it did in pre GPS days.

    Some tramp steamers as late as WW2 would reset their clocks at local apparent noon each day, the result being days of all sorts of odd lengths.
    The norm however was to put the clocks forward by half an hour or a full hour - depending on the ship's speed - at midnight so that 'noon'/mer. pass. the following day would fall close to 1200 clock time.
    I thought ships advanced/retarded their ‘ships clocks for local time’ at the dogs? Or is that just an RN thing?
    Semper aliud

  3. #13
    Join Date
    Nov 2009
    Location
    currently in Pto Montt, Chile
    Posts
    217

    Default Re: Length of day at high latitudes?

    Quote Originally Posted by john_morris_uk View Post
    I thought ships advanced/retarded their ‘ships clocks for local time’ at the dogs? Or is that just an RN thing?
    Mustafa Bin a navy thing...
    Typically in MN clocks would be changed at midnight but the time lost (ie shorter watch ) would be shared between the 8-12, 12-4 and the 4-8.. If westbound the C/O would let the 2/0 and 3/0 suck up all the extra time on watch.. Varied a bit between companies and ships but MN doesn't have 'dogs'....

    Same same the date line.... gain a day? Oh look its a week day...! Lose a day?.... ooops there goes our day of rest....

  4. #14
    Join Date
    Jul 2006
    Location
    Emsworth Hants
    Posts
    12,116

    Default Re: Length of day at high latitudes?

    >Surely a day is the same at all latitudes,

    Our skydiving team was jumping a Hercules in Sweden and it didn't get dark until midnight, in the Caribbean it is 12 hours of darkness and 12 of light.

  5. #15
    Join Date
    Nov 2009
    Location
    currently in Pto Montt, Chile
    Posts
    217

    Default Re: Length of day at high latitudes?

    Quote Originally Posted by KellysEye View Post
    >Surely a day is the same at all latitudes,

    Our skydiving team was jumping a Hercules in Sweden and it didn't get dark until midnight, in the Caribbean it is 12 hours of darkness and 12 of light.
    Yes but.....

    Hours of daylight vary by latitude and season...

    A navigator's day runs from 1200 to 1200 ( ship's time ) ... whether that be a 23 hour day or a 25 hour day or something in-between...

  6. #16
    Join Date
    Mar 2007
    Location
    Atlantic
    Posts
    18,348

    Default Re: Length of day at high latitudes?

    Quote Originally Posted by Frank Holden View Post
    Yes but.....

    Hours of daylight vary by latitude and season...

    A navigator's day runs from 1200 to 1200 ( ship's time ) ... whether that be a 23 hour day or a 25 hour day or something in-between...
    Did you ever run noon to noon UT? For navigation purposes rather than crew watchkeeping in Local?

  7. #17
    Join Date
    Nov 2009
    Location
    currently in Pto Montt, Chile
    Posts
    217

    Default Re: Length of day at high latitudes?

    Quote Originally Posted by capnsensible View Post
    Did you ever run noon to noon UT? For navigation purposes rather than crew watchkeeping in Local?
    Nope.... day was always to 1200 ship's time..... however ...

    On the Union-Castle mail ships we would leave Southampton on GMT ( or BST ) and not touch the clocks until 2 ( or 1 ) nights before Capetown despite going well west around the bulgy bit of Africa.... so as not to confuse the passos...

    For much of the trip mer alts were something the 2/0 did in the middle of the afternoon to keep himself amused .... 'day's run' was calculated using 'sun-run-sun' and two Marq St Hilaires.....

    ¿Qué 'UT'? ... sounds positively Bonapartiste....

  8. #18
    Join Date
    Mar 2007
    Location
    Atlantic
    Posts
    18,348

    Default Re: Length of day at high latitudes?

    Thanks and bless our aviator friends for Air Navigation Tables and the fact that Greenwich got there first, not Paris.

  9. #19
    Join Date
    Feb 2004
    Location
    Boat (now back in) the Clyde
    Posts
    5,165

    Default Re: Length of day at high latitudes?

    Wow 50 degrees is high latitude. Think only Lizard Point in Britain is the only place in lower latitudes then.

  10. #20
    Join Date
    Nov 2008
    Posts
    6,717

    Default Re: Length of day at high latitudes?

    Quote Originally Posted by dunedin View Post
    Wow 50 degrees is high latitude. Think only Lizard Point in Britain is the only place in lower latitudes then.
    Yes, that's what I was thinking. Sailing on the West Coast, I never really thought of myself being a rufty-tuffty High Latitude sailor.

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