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Thread: Tide Constants

  1. #1
    Join Date
    Mar 2010
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    me : Pwllheli Boat : Arisaig
    Posts
    268

    Default Tide Constants

    Just planning a solo sail from Arisaig to Pwllheli in 2 weeks time and plan on departing from Scotland after overnighting in The Sound of Gigha.
    In the sailing directions for the Sound of Gigha it states after N going and S going times:-
    "Constant is approximately -0200 Oban (+0500 Dover) at springs, and -0500 Oban (+0300 Dover) at neaps"
    And after 28 years of big boat sailing I suddenly realise I haven't a clue what it means. Mr Google has said something about harmonic tides and simple tides and has left me no wiser.
    Can any one enlighten me please
    Mike

  2. #2
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,057

    Default Re: Tide Constants

    Quote Originally Posted by Vegable View Post
    Just planning a solo sail from Arisaig to Pwllheli in 2 weeks time and plan on departing from Scotland after overnighting in The Sound of Gigha.
    In the sailing directions for the Sound of Gigha it states after N going and S going times:-
    "Constant is approximately -0200 Oban (+0500 Dover) at springs, and -0500 Oban (+0300 Dover) at neaps"
    And after 28 years of big boat sailing I suddenly realise I haven't a clue what it means. Mr Google has said something about harmonic tides and simple tides and has left me no wiser.
    Can any one enlighten me please
    Mike
    Add ( when positive) subtract (when negative) the figures ) 0200, 0500, etc to/ from the times of HW at the standard ports Oban or Dover to get the times at the secondary port ( or in this case the Sound of Gigha)
    Interpolate for tides between springs and neaps.

    From the almanac the north going tide begins at HW Oban + 0430 and the south going at HW Oban -0155
    Last edited by VicS; 23-04-19 at 16:19.

  3. #3
    Join Date
    Mar 2010
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    me : Pwllheli Boat : Arisaig
    Posts
    268

    Default Re: Tide Constants

    Thanks Vic.
    As soon as I read your answer it came back to me. A senior moment.
    Mike

  4. #4
    Join Date
    Feb 2005
    Location
    Guernsey
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    3,382

    Default Re: Tide Constants

    An important word is 'approximate'.
    Also, the differences will change during the lunar cycle.
    On the internet no one knows you are a donkey.

  5. #5
    Join Date
    Sep 2005
    Posts
    3,409

    Default Re: Tide Constants

    Quote Originally Posted by guernseyman View Post
    An important word is 'approximate'.
    Also, the differences will change during the lunar cycle.
    Indeed so. Pretty silly for the author of those sailing directions to call it a ‘constant’.

  6. #6
    Join Date
    Mar 2010
    Location
    Sunny Northumberland
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    1,011

    Default Re: Tide Constants

    I believe that Gigha is near an amphidromic point, so the tide range and rate are likely to be unusually small there.

  7. #7
    Join Date
    May 2007
    Posts
    35,815

    Default Re: Tide Constants

    Quote Originally Posted by guernseyman View Post
    An important word is 'approximate'.
    Also, the differences will change during the lunar cycle.
    That's why they give a springs figure and a neaps figure.

  8. #8
    Join Date
    May 2007
    Posts
    35,815

    Default Re: Tide Constants

    Quote Originally Posted by Baddox View Post
    I believe that Gigha is near an amphidromic point, so the tide range and rate are likely to be unusually small there.
    Height range is small, doesn't mean there's no stream though.
    ISTR nearly 2 knots?

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