New Test Data for Keel Loads

Discussion in 'Sailboats' started by Remmlinger, Jan 11, 2011.

  1. Remmlinger
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    Remmlinger engineer

    The following test results might interest the design community.
    I have measured the loads on the keel/hull junction during water impact. It turned out that the conventional design practice might result in a structure that is too week, especially for yachts with a low ballast ratio and a large keel area. The complete test results can be downloaded from my website www.remmlinger.com
    Any comments would be appreciated

    Ulrich
     
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  2. Perm Stress
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    Perm Stress Senior Member

    Many thanks for efforts!
    Now I am busy with reading your report.
     
  3. Perm Stress
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    Perm Stress Senior Member

    In your article, Reynolds number is actually left out of all considerations.
    In ship hydrodynamic research Reynolds number effects are always considered both when designing and performing an experiment and in analysis of results.
    As to keels, at least when lifting properties of keel and rudder are important, it is highly desirable to keep Re>~100'000 as an absolute minimum, for qualitative similarity of flows. This I know from literature and from own sailboat modeling.
    I would suspect, that in water-impact process as here Reynolds number should also have strong influence. Did you more research in to this topic, as is published in your article?
     
  4. Remmlinger
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    Remmlinger engineer

    Thank you for the careful study of my paper. Upon your comment I have revised page 3 of my paper, where I discuss the influence of Reynolds number. At water impact, the high loads occur during the very first moment, when only inertia forces play a role and frictional forces are negligible. I have added a citation of measurements that prove the independence of Reynolds number.
    Regards
    Ulrich
     
  5. SuperPiper
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    SuperPiper Men With Little Boats . .

    Yep, I read it. It's written in the style of the old NACA/NASA documents. I didn't even attempt to follow the math because most of it is developed in the references outside of the drop test document.

    The INTRODUCTION is clear and concise. The test procedure seems to be sound and rigorous. I sometimes lost track of whether the dimensions were in the model or the full scale domain. The references to highway impacts was brilliant.

    So to summarize the article: the crew inside a sailboat is likely to receive injuries if a (heeled) boat free-falls off a 2.1m crest; and, a boat should be designed for a free-fall height of 10m in order to keep its keel and to get its injured crew to safety.

    Did I get it right?
     
  6. Remmlinger
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    Remmlinger engineer

    That is exactly right. The current design practice would allow a drop height of approx. 2.1m meters for the hull and even less for the keel. Obviously people hope that their boat will never fall off a breaking wave that is higher than 2.1 meters. May be they manage to avoid storms or are able to steer clear of breaking waves. Since I have worked as a delivery skipper during all seasons, I doubt this being possible. Therefore I would recommend a much higher design drop height. A design for 10 meters would double the structural weight of the boat, compared to the current design practice, but I would accept this weight penalty for the peace of mind that I get for it.
    Ulrich
     
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  7. Guillermo
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    Guillermo Ingeniero Naval

    Very interesting work, Ulrich.
    Have you brought it to the attention of ISO 12215 Working Group 18?

    Cheers.
     
  8. Remmlinger
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    Remmlinger engineer

    Good point!! Yes, in October last year I sent a copy to Gregoire Dolto.
    He answered that it is too late to consider the results for an incorporation into the new ISO 12215-9.

    Since ISO is a non-governmental organization, funded by organizations like EBA and ICOMIA, their interest in new test results that might lead to heavier scantlings making the boats more costly, seems to be low. If a ship yard were forced by ISO to put more material into the boat and the end user is not willing to pay for it, the ship yard would loose money. I guess one has to inform and even educate the end user first. The pressure for a better design has to come from the market. As a first step I got my paper published in the latest IJSCT.

    Best regards and thanks for your interest
    Uli
     

  9. Guillermo
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    Guillermo Ingeniero Naval

    Thanks Uli.
    In my opinion although perhaps it is late to take into account your findings for the forecoming ISO 12215-9, the WG 18 should consider them for future amendments.

    As you probably know, Robin Lombscombe, who is also a member of the WG 18, has developed a Keel Checker based in the ISO, freely available through ICOMIA and Southampton Solent University (http://www.icomia.com/news/news.aspx?NewsId=240).

    It would be most interesting to have a keel checker which takes into account your findings. Perhaps some "safety-first oriented" blue water sailing boats' designers/builders would be interested.

    Cheers.
     
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