Page 1 of 17 12345611 ... LastLast
Results 1 to 10 of 161
  1. #1
    Join Date
    Jan 2010
    Posts
    6,031

    Default Wind against tide - physical reasons why this is dangerous ?

    Hi,

    I keep reading that conditions often become rough when the wind is against the tide and I'm curious to know the physical reasons why this is so ? Obviously you need to add the windspeed to the tide speed to get an idea of how much of a sea will result, but if the wind is say 30 kt and the tide is 4 kt, does the resulting effect amount to worse conditions that a wind of 34 kt would have given ? From what I've read the answer is "yes", but I'm interested to know what is going on for that to be true ? Is it an interaction with the sea bed or what ?

    Thanks,

    Boo

  2. #2
    Join Date
    Jun 2009
    Location
    south yorks
    Posts
    5,435

    Default difference in speed

    In simplified terms the tide changes the shape of the wave. It slows the deep part of the wave in relation to the top of the wave, sort of trips the wave up.The waves become higher and unstable and start to break

  3. #3
    Join Date
    Nov 2003
    Posts
    28,184

    Default

    Basically, the wind gets under the waves and makes them stand up, so they will be steep and choppy, hindering your forward progress.
    Excellent thread here on Cruisers Forum....

    http://www.cruisersforum.com/forums/...ide-32570.html
    'East Coast Pilot' at www.eastcoastpilot.com 4th Edition now available......

  4. #4
    Join Date
    Mar 2006
    Location
    The island of Alderney
    Posts
    2,536

    Default

    We had an interesting one yesterday while drifting in a tide of 2kn, a ferry went past (at 3 cables) and when the wake eventually arrived it was moving diagonally across the tide. You could plainly see the waves grow in height and then fall over themselves into breakers.

    I hope that description helps?

  5. #5
    Join Date
    Jul 2009
    Location
    East Coast
    Posts
    1,526

    Default

    Quote Originally Posted by Boo2 View Post
    Hi,

    I keep reading that conditions often become rough when the wind is against the tide and I'm curious to know the physical reasons why this is so ? Obviously you need to add the windspeed to the tide speed to get an idea of how much of a sea will result, but if the wind is say 30 kt and the tide is 4 kt, does the resulting effect amount to worse conditions that a wind of 34 kt would have given ? From what I've read the answer is "yes", but I'm interested to know what is going on for that to be true ? Is it an interaction with the sea bed or what ?

    Thanks,

    Boo
    It does seem to get a bad press.

    But the other direction, down wind, is a vote grabber !

    In a F6 & F7 it's as good as sailing gets. Finding a good enough reason for going in an opposite direction than you intended is often the problem though. Normally to do with going back to work.
    It is never too late to have a happy childhood. Buy a boat.

  6. #6
    Join Date
    Apr 2007
    Posts
    2,290

    Default

    It shortens the wavelength of the waves, making them steeper.

    The wind is not necessary for the effect, albeit it does make things worse, as a train of waves from the open sea encountering an area of strong tidal flow will steepen and tend to break. It can get pretty bad even on a calm day in some specific areas where a large swell encounters a strong ebb.

    If the tidal flow is in the opposite direction, i.e. wind with tide, the wavelength will increase and the sea will feel smoother and calmer.

  7. #7
    Join Date
    Sep 2004
    Location
    Victoria BC
    Posts
    996

  8. #8
    Join Date
    Jul 2001
    Location
    Lorient, just back from a second round Atlantic trip
    Posts
    3,167

    Default

    It does not explain anything about physics, but this graph (I think it comes from the Scripps Institution of Oceanography) gives some insight into the relationships between wave characteristics (length/height, curves L and H) and current speed (related to wave period/celerity, horizontal axis); it may also give an idea why in a tide against wind situation some waves break and some do not.


    [/URL]



    the full description can be found here

    http://sybrancaleone.blogspot.com/20...l-streams.html
    oh no, yet another sailing blog
    http://sybrancaleone.blogspot.com/

  9. #9
    Join Date
    Feb 2010
    Posts
    2,243

    Default

    Quote Originally Posted by Roberto View Post
    It does not explain anything about physics, but this graph (I think it comes from the Scripps Institution of Oceanography) gives some insight into the relationships between wave characteristics (length/height, curves L and H) and current speed (related to wave period/celerity, horizontal axis); it may also give an idea why in a tide against wind situation some waves break and some do not.


    [/URL]



    the full description can be found here

    http://sybrancaleone.blogspot.com/20...l-streams.html
    Very simple and clear description..useful thanks

  10. #10
    Join Date
    Jun 2005
    Posts
    18,628

    Default

    Sea bed interaction nearer the shore is extremely important. The other effect, not mentioned is that the relative wind speed is increased by the current
    If I'd wanted to live in a Banana Republic I'd have gone to South America.

Page 1 of 17 12345611 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Find Boats For Sale

to
to