Dynamic loads on canting keels

Discussion in 'Stability' started by GERGF3, Jul 10, 2007.

  1. GERGF3
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    GERGF3 New Member

    Hello,

    I am a naval architecture student from Germany and I am writing my diploma-thesis at the moment. It is about "dynamic loads on the canting keel of the sailing yacht sailOvation".

    Maybe I am the first student in Germany who is working on this case and my problem is that there is no useful literature.

    Is anybody in this community who can help me?I need some ideas form my thesis.

    Thank you,
    Gregor
     
  2. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    I am only guessing, but I think the largest loads is when the bulb and the keel is up in the air.
     
  3. marshmat
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    marshmat Senior Member

    Gregor,
    The reason you can't find any useful literature on your subject is because virtually all of the useful literature on large canters is proprietary and confidential.
    The static loads- simply holding the weight of the bulb at whatever angle- are simple. Am I correct in saying, Gregor, that what you're studying is not this problem (a simple cantilever) but, rather, the additional loads due to hydrodynamic forces, the motion of the boat, and intersecting the water surface?
     
  4. MikeJohns
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    MikeJohns Senior Member

    Raggi
    Yes but dynamic events. For example dropping into a trough with the keel horizontal .

    cheers
     
  5. CT 249
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    CT 249 Senior Member

  6. MikeJohns
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    MikeJohns Senior Member

    Hi Chris

    This is always the problem with complex dynamic loads and why scantling rules and new inovation through such vehicles as the ABS "5 year rule" are accepted practice in an era of powerful computers and sophisticated software.

    I think there are some rather slim FOS on some bulb keel designs and a tendency for some designers to ignore (or be ignorant of) serious fatigue strength issues in their designs.

    We get similar arguments going through the courts wrt rig failure.

    I know from acting as expert witness that it doesn't take much technical obfuscation to make the court indecisive, a classic case of a tribunal being a better choice than an adversarial hearing. [Although in the link you posted the verdict was decisive.]
     
  7. Windvang
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    Windvang Yacht Designer

  8. GERGF3
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    GERGF3 New Member

    Thank you for your help. The paper about the VO70 is quite useful. The link below shows a pic of the SailOvation, the Yacht i am writing about.

    http://www.segeln-magazin.de/sailovation/images/350pixSOV_5_100706.jpg

    I am going to do seakeeping tests on bord with an installed acceleration measurement system. i will use the data for a FEA calculation.
     
  9. GERGF3
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    GERGF3 New Member

    Is anybody knowing anything about the dvpp peter ottosson developed?
     
  10. yades
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    yades Senior Member

  11. hbr
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    hbr Junior Member

    Gregor,

    did you finalised your thesis and do you want to share some info about your thesis?
     
  12. Pericles
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    Pericles Senior Member


  13. Chris Ostlind

    Chris Ostlind Previous Member


    Great set of observations. I posed a question related to this scenario regarding canters back in January and still, as you indicate, there is precious little from which to draw conclusions as to the overall dynamic loads being spread through the boat due to the effect of the canted keel.

    Quote: Chris Ostlind from post #103 S/H Battle of the Canters http://www.boatdesign.net/forums/showthread.php?t=14833&page=7

    "Furthermore, what was most startling was that fully 38% of the boats with canting keels that were supposed to start the race had to fall out or not start at all due to demolished masts. Since when is that a statistic to crow about? If it had been a bunch of different maladies that had mysteriously befallen the canting fleet, then you could say it was an unfortunate run of bad luck. When it's all due to mast failure, you can't simply ignore the fact and start tossing kudos for a job well done. How many boats of the non-canting variety had their masts taken down in the very same conditions? Was it equally as problematic when looking at a percentage of the traditional keel fleet?

    Nearly 40% failure, out of the event, all from the same problem...? That has seriously problematic written all over it. I'm willing to be corrected on this position, but I still haven't seen any info that would tell the story differently. Perhaps Randy could shed some light on the stress issues for canting keel equipped boats and how that loading is pushed through the rig under the stress of racing?"



    One of our well-known Forum posters had this for a response, which indicates the distance of the typical boating enthusiast from what could be really going on with these boats:


    Quote: Doug Lord from post #111 S/H Battle of the Canters page 8

    “The rig doesn't give a hoot what’s under it: a canting keel, two or three hulls, or a belly full of lead-just so long as it is designed and built properly for the RM developed by whatever means. There is absolutely no association whatsoever between canting keels and rig failures-or at least there shouldn't be. The science of rig design and construction for a given RM has been around generations longer than have canting keels. The only area I can see any possible guilt by association is in the fact that the masts have come down on racing sailboats....”


    Now, here it is, some 7 months later and still there is pretty meager pickings from which to draw something like a solid set of conclusions. If anybody out there manages to glean any inside info from the various canting keel sources available, I sure would like to know what is being modeled to deal with this issue.

    btw... Nice sources, Chris and Windvang.
     
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