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  1. #1
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    Default A Lesson in Physical Chemistry

    The saying that we learn something new everyday applies very well to sailing.

    The boat is coming out tomorrow and so I locked in to Heybridge Basin on yesterday's tide. Nasty morning, blowing top end of an 8 from the NE but at least it gave me a slant for the lock. Dropped the main and continued under storm jib only (still went past the withies at 4kts!), all fine and tied up in the lock. The lesson came when it was time to open the inner gates. It took three of us to open the first one and I asked whether one of the bearings had failed. The answer was that the fresh/salt water are so reluctant to mix that it holds the gates up. I was amazed; I knew salt and fresh don't like one another due to specific gravity, but not that it could result in such a marked resistance. It really took some pushing.
    "I thought my daffodils were yellow until I met Joe Kennedy."

  2. #2
    Join Date
    Feb 2007
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    Essex
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    22,857

    Default Re: A Lesson in Physical Chemistry

    Very good. I'll use that next time my wife complains that the heads seacock is stiff.
    Far away is near at hand in images of elsewhere

  3. #3
    Join Date
    May 2001
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    UK East Coast
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    36,535

    Default Re: A Lesson in Physical Chemistry

    Quote Originally Posted by Major_Clanger View Post
    The lesson came when it was time to open the inner gates. It took three of us to open the first one and I asked whether one of the bearings had failed. The answer was that the fresh/salt water are so reluctant to mix that it holds the gates up. I was amazed; I knew salt and fresh don't like one another due to specific gravity, but not that it could result in such a marked resistance. It really took some pushing.
    Logically, the higher density of salt water would result in the contents of the lock exerting pressure to try to open the gates, not prevent them being opened.

  4. #4
    Join Date
    Oct 2016
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    Currently Suffolk
    Posts
    1,079

    Default Re: A Lesson in Physical Chemistry

    Quote Originally Posted by pvb View Post
    Logically, the higher density of salt water would result in the contents of the lock exerting pressure to try to open the gates, not prevent them being opened.
    Yes, except that the inner gates open inwards, toward the lock.
    "I thought my daffodils were yellow until I met Joe Kennedy."

  5. #5
    Join Date
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    Default Re: A Lesson in Physical Chemistry

    Quote Originally Posted by Major_Clanger View Post
    Yes, except that the inner gates open inwards, toward the lock.
    Are we talking about the same lock?

    Screenshot 2018-11-21 at 17.44.56 copy.jpg

  6. #6
    Join Date
    Jun 2009
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    From the Needles to the Nab, from Cowes to St Catherine's
    Posts
    4,788

    Default Re: A Lesson in Physical Chemistry

    If they opened inwards what would keep them shut when the lock was emptied of water?
    Substance over style

  7. #7
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    Default Re: A Lesson in Physical Chemistry

    Quote Originally Posted by pvb View Post
    Are we talking about the same lock?

    Screenshot 2018-11-21 at 17.44.56 copy.jpg
    Quote Originally Posted by Little Grebe View Post
    If they opened inwards what would keep them shut when the lock was emptied of water?
    We are talking about the same lock and I'm talking nonsense! The inner gates do indeed open outwards, towards the canal. I can only blame it on going straight to the pub afterwards to warm myself up.
    "I thought my daffodils were yellow until I met Joe Kennedy."

  8. #8
    Join Date
    Jul 2007
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    Home-Sidcup, boat-Lower Halstow, Kent, England
    Posts
    567

    Default Re: A Lesson in Physical Chemistry

    Surely the gate being difficult to open is more likely to be a greater flow of water coming down the canal due to the heavy rain of the last few days, or the levels not quite even.

  9. #9
    Join Date
    May 2001
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    Norfolk/Suffolk
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    3,054

    Default Re: A Lesson in Physical Chemistry

    Quote Originally Posted by FulmarJeddo View Post
    Surely the gate being difficult to open is more likely to be a greater flow of water coming down the canal due to the heavy rain of the last few days, or the levels not quite even.
    What I Thought
    Harwich for the Continent - Brexit For the Incontinent . Sadler 290

  10. #10
    Join Date
    Oct 2016
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    Currently Suffolk
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    Default Re: A Lesson in Physical Chemistry

    Extra water in the canal can make little difference surely? If levels between lock and canal are equalised, which obviously they were, then all that has changed is a slightly higher level in the canal to push against (and we're talking an inch or so). I was surprised at the amount of effort needed to get the first gate started and thought that something had gone awry, but the lock-keeper must have experienced it countless times, and was sure it was fresh and salt water meeting.
    "I thought my daffodils were yellow until I met Joe Kennedy."

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