The perils of edgy design offshore

Discussion in 'Sailboats' started by CutOnce, Jul 18, 2011.

  1. Ad Hoc
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    Ad Hoc Naval Architect

    A typical sailing catamaran in the 10-13m range. As noted, unless of course you wish to provide the GZ curve of the cat's you posted to be more "accurate" as you seem to imply?

    Your understanding of your own question.

    Where does my GZ curve state it is a 50knot wind? It doesn't. You claimed that cherry picking is present in racing, viz:

    The curve shows quite simply a wind producing a wind heeling moment. The wind can be ANY wind you care to select. Your premise is that there is a double standard. Given a nominal wind heel, when overlaid onto 2 very different vessels, the result is clear to see. One would capsize, the other not, by a very clear and obvious margin.

    So, please explain where the double standard is..?
     
  2. Doug Lord
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    Doug Lord Flight Ready

    The Perils of Edgy Weather in Any Boat

    ==================

    =================

    Mr. Wiley, if you'll reread my post you'll see that I did post numbers that cover the real world sailing of a typical racing cat.
    Further, the point is that in a race these boats are sailed at a much greater angle of heel that mentioned by Mr.Hoc and are most always raced on the
    edge of a capsize/pitchpole to reduce wetted surface by keeping the weather hull out of the water. They are the essence of edgy boats sailed in an edgy manner-in a manner that a capsize or pitchpole may only be a split second away. Yet they are allowed to race in the Chi-Mac with no problems
    from the powers that be. Of course, I think it is right that they are allowed to sail and race.
    My problem is that there seems to be a standard in peoples minds for monohulls where the idea is to reduce risk to nil while there is a standard(rightly) that allows high performance multihulls to race with no restrictions on how they are sailed when that can be a very risky proposition in a race.

    ---
    As I said before, I 100% support the "Findings" and Recommendations of the report and hope that their implementation will produce much better, faster and safer boats without in some way discouraging design innovation. Time will tell.
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Woaah..missed that.

    Please show me the posting that provides the GZ curve of the high performance racing catamarans that you are happy with to use as a basis.

    Please show me where this posting is with said graphs.
     
  4. MikeJohns
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    MikeJohns Senior Member

    Marc
    It has happened, these sorts of boats are very old and poor designs that are prohibited in most races and have been for decades. If you want a better safer and faster boat they are out there in droves.

    As to how to improve the boat; look at the commentary as to what's wrong with it. The improvements are then self apparent.

    This is an antiquated design that was condemned from the start by racing sailors as well as professional designers. Much better boats have evolved since then.
     
  5. daiquiri
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    daiquiri Engineering and Design

    They are actually flown at angles much below where their maximum RM is, and hence not on the edge of a capsize. The windward hull has to be out of water, as you mention it, in order to reduce the water resistance. But it also has to be very low above water (ideally just above the water surface) in order to reduce the aerodynamic resistance and to prevent an excessive decrease of the driving force by sails (due to heel).

    What Ad Hoc wanted to show (I presume) is something you probably already know (perhaps expressed in another terms) - a huge difference in stability between monohulls in general (and Wingnuts in particular) and cats, for the same heeling moment. And that is essentially a condition similar to the one which capsized Wingnuts - with sails reefed and hence wind-induced heeling force acting on just the hull and poles. It means that a cat of a similar size and weight might have been able to withstand the wind force better than Wingnuts could. All of that is to say that in some critical situations Wingnuts' behavior cannot be assimilated to a behaviour of a similarily-sized cat, and neither can be it's degree of safety.

    I essentially agree with this statement, if you cancel the words "to nil" and if we exclude Wingnut's design from it. It is a boat with some critical stability issues, as has been shown both here and in the accident report.

    Cheers
     
  6. Doug Lord
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    Doug Lord Flight Ready

    The Perils of Edgy Weather in Any Boat

    ---------------------
    Slavi, as soon as the windward hull of a cat or the main hull of a tri leaves the water-even just 1mm- it is at(or just past) max RM-RM only decreases from that point. Of course that depends on where the crew is . But assuming that the crew is max to weather and/or in their normal maximum racing position as soon as the weather hull leaves the water -that is maximum RM.
    I've sailed and raced multihulls for many, many years and when you fly the windward hull on a cat you'd better be on your toes. Their is no comparable
    "risk" associated with a properly designed monohull keelboat-except maybe downwind in a lot of wind with big waves and the spin set.

    From Woods design website( http://www.sailingcatamarans.com/stability2.htm )

    click on image:
     

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  7. troy2000
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    troy2000 Senior Member

    Doug, in an offshore race lasting two or three days, how much time will a catamaran spend flying its windward hull? Honest question; I know little about them.
     
  8. daiquiri
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    daiquiri Engineering and Design

    True Doug, I've just realized the nonsense about max. RM I have written. All the rest remains valid. Evidently it's time here to go to sleep. Cheers to everyone! :)
     
  9. Doug Lord
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    Doug Lord Flight Ready

    The Perils of Edgy Weather in Any Boat

    ==============
    As much is possible* because the gains are substantial getting the windward hull out of the water. It also, of course, depends on the conditions- because the risk is much higher when flying a hull prudence may dictate a more cautious approach with some skippers.
    The point in my earlier discussion is that this is how these boats are sailed when racing-it is risky and it is normal. It is much more risky on a regular basis
    in normal conditions than even racing a poorly designed(apparently) boat like WingNuts in normal conditions-and therein lies the crux of the contradiction I just can't get out of my head.

    *Keep in mind I'm talking about high performance multihulls-cruising multihulls rarely fly a hull.
     
  10. peter radclyffe
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    peter radclyffe Senior Member

    most multihulls do not have an edge which digs in,so does not flip so easily

    which is what makes wingnuts, in particular , so dangerous

    a multihull is less affected by the sea than wingnuts
     
  11. MikeJohns
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    MikeJohns Senior Member

    But on one hand you have a chosen and well understood danger like flying-a-hull that action will be done with skill and understanding. When you reduce sail and slow down it becomes considerably safer. So you have a choice and you choose to compromise the safety, you can later choose to adopt a safer course of action if the weather picks up or night falls, or you get exhausted or ill.

    The other type you are comparing this with is an intrinsically poor design for a monohull to be used offshore, with characteristics that make it treacherous to be aboard in bad weather. There is no equivalent. You can't slow down and drop sail to make the boat intrinsically safer when it's intrinsically unsafe.
     
  12. Gary Baigent
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    Gary Baigent Senior Member

    From Ad Hoc,
    "Oh dear, someone with delusions of grandeur that is incapable of logical reasoning and theorising based upon observations to produce consistent and repeatable engineering knowledge open to any independent scrutiny."

    "So, the book by Issac Netwon "Philosophiæ Naturalis Principia Mathematica" published in 1687, is now out of date. Ergo F=MA is no longer valid??..hmmm interesting...tell me more"

    Oh dear, Ad Hoc, the delusions apply to you with you ridiculous and ignorant 2 degree heeling catamaran (obviously you've never sailed one but can draw an inept, inaccurate graph, as if that will suffice) - but my point is that knowledge continues and aside from your silly overkill smugness in introducing the Newton figure, old thoughts ARE overtaken, new skills ARE developed (talking sailing - what would Issac think of the astonishing foiling Moth sailors for instance, that would be light years away from what he would have envisaged sailing to be, he'd probably suffer from immediate dropsy) - and the same applies to edgy other designs; humans are incredible and can surmount many of the established thoughts and principles formerly accepted as sacrosanct.
    And obviously, you and MJ adhere to the latter - stuck in a time warp, say late 17th Century. By the way, aside form your superior posturing, why haven't we seen examples of yours and MJ's perfect designs on this forum? I'm sure many wait with bated breath.
     
  13. Willallison
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    Willallison Senior Member

    Actually, I rather think that Isaac would be rather pleased with himself... all that FACTUAL physics put to such exciting use....
     
  14. MikeJohns
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    MikeJohns Senior Member

    One of the principle tenants of Naval Architecture is that there can be no perfect design. Just the best call on the juggling of compromises. And what is perfect? in your world maybe the fastest and most dangerous for the thrill or for another the fastest and the safest (compromised already) and again for another the most comfortable and reliable plodder ....... first you need to define perfect! The perfect boat for all uses is an oxymoron.

    It would be good if you had enough conviction to nail your colors to the mast rather than all the polemics. Then we can look at specifics.

    Do you really think Wingnuts was seaworthy and suitable for the conditions?
     

  15. Gary Baigent
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    Gary Baigent Senior Member

    We're talking about "edgy" (meaning high performance) race boats here, MJ, quite simple, nothing to do with plodders, not much to do with compromising. I noticed that you slime-d away from Upcurchmr's question about what you would do to improve the O.J. Rogers boat. So here's your chance; at last we will be able to see the renderings and figures of the superior "phantom" MJ design, a winner, maybe even a breakthrough. All of us here ... abated breathing.
     
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