Sail Loading on Rig, Rig Loading on Vessel

Discussion in 'Sailboats' started by brian eiland, Oct 14, 2003.

  1. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Guest - don't worry, I don't feek taunted. Maybe I should have included a bigger smiley ;-)))

    Steve
     
  2. SailDesign
    Joined: Jan 2003
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    Location: Jamestown, RI, USA

    SailDesign Old Phart! Stay upwind..

    Ahem! That should be "feeL taunted" with an "L" not a "K".
    Sounds like a sensitive geek......
     
  3. brian eiland
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    brian eiland Senior Member

    New Mast Design Software -IBI news

    dvgale just recently posted a reference to this article that I felt might be applicable down the road in this discussion when we get back to it. BE
    _________________________________________

    Dutch team completes Best Mast project

    By IBI Magazine

    A joint project involving the marine industry and a number of research organisations in the Netherlands to develop a simulation model that can be used to calculate the peak loads experienced by masts and rigging is approaching its completion.

    The Best Mast project was led by Nirvana Spars, and also involved Maritime Research Institute Netherlands (MARIN), the Centre of Lightweight Constructions (CLC) - a joint venture between the Technical University of Delft and research organisation TNO - with input from Jongert, the well known Dutch boatbuilder.

    The CLC was responsible for developing a computer model to convert wind load into loading on a boat's mast and rigging. Another key participant in the project, MSC Software, was responsible for converting loads on masts and rigging into anticipated stresses and patterns of deformation.

    As Nirvana Spars notes, aluminium is gradually making way carbon-based composites in many masts because the new materials are lighter and stronger, but exploitation of the full potential of the new materials has been limited, primarily by the lack of data available about exactly what kinds of forces a mast needs to endure.

    Nirvana Spars says one of the key benefits of the project is it will help it to understand much more about the forces that masts and rigging have to absorb under different conditions. Currently, masts are manufactured with a built-in safety margin, in order to try to prevent them from snapping, but this sometimes makes for an unnecessarily heavy last, the company believes.

    To-date, Nirvana Spars has specialised in aluminium masts, but has completed a new carbon fibre facility in which it has so far built five carbon fibre furling booms.

    Using the data collected, Nirvana Spars anticipates that the computer model will be able to predict the loads that a mast will experience and enable the company to optimise the design of a mast before it enters production, and thus obtain the maximum possible reduction in weight whilst ensuring that the mast remains strong enough not to fail.

    Nirvana Spars' General manager Sander Rusche told IBI that the computer model was now completed, and that its accuracy was being tested against Ôreal worldÕ data collected by sensors on a boat made available by Jongert, Flying Magic.

    "We aim to have a demonstration system available for people to see at the Monaco Boat Show in September," Rusche told IBI.

    David Foxwell

    (15 July 2004)
     
  4. wafi
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    wafi Junior Member

    I believe the "easy" way to look at righting arm is the best you could do. Only classification company I know, who make some statements for "simple" rigg configurations and loads is German Lloyd. Of course, based on righting arms.

    Peter
     
  5. MikeJohns
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    MikeJohns Senior Member

    Rig loads

    It can be a pretty exact science now, the real numbers taken from the real world give close results to the older scantling rules. Unfortuantely most of the leading edge FEA on rig loads is not in the public domain but is the property of the consortiums and designers behind the America's cup boats. Given the relatively low cost of strain gauges and recording instruments (one laptop) it is quite easy to log maximum rig loads over a large range of sailing conditions. But like I said the scantling rules give a pretty close match to the designs we have done.
     
  6. conny
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    conny New Member

    easy solution

    just fit our pbo rigging ;) (www.smartrigging.com)!

    In all the stays a smart fibre is fitted, which measures the stress full time
     
  7. wafi
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    wafi Junior Member

  8. brian eiland
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    brian eiland Senior Member

    Interesting Sites

    Thanks, those are both interesting sites. I will spend a little more time looking at them upon my return from Thailand
     
  9. Lda
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    Lda Junior Member

    Concerning classic gaff rigs and wooden masts, I guess that computer estimates are specially difficult to make because those riggings are very flexible and the forces needed to "move" and accelerate the mast and gaff according to boat and spars movements are a substancial part ot the total, which is much less the case with lighter and much more rigid modern materials and bermudian rigs. I had the opportunity to work on a #1900 21' waterline racing (and seagoing...) gaff cutter with what looks like original mast and spars. Scantling looks not reasonable by "modern" (#1950..) standards although it lasted 100 years... Also its gaff and topsail spars use an elaborate cable fretting technic I had never seen before. Of course this technic implies that those spars need to be substancially bent in normal working conditions. I understand that those practices were about discontinued in the 30' or 50', possibly due to the progresses of calculus which convinced engineers to use much more rigid, and easier to modelise systems. Looks like AC boats are now returning to much more flexible solutions. Point is you won't find modern AC-like computer modeling technics already applied to non-exotic materials (if you can find modern AC like technical litterature published on the market anyway...). So your choice could be either to use 1950' or 1960' litterature which relates to rather rigid materials and assemblies, mainly because of limitations in modelling technics in those days, and which demands heavy scantlings as a consequence of this, or to use much less argumented scantling rules of 1900, which should be somewhat lighter and not necessarily weaker, provided corresponding materials and assemblies are in accordance with the practice of the days (ie: flexible enough...).
    If you have some time and money you can also consider making a complete modern computer modeling and analysis of classic gaff riggings (got 10.000.000$ just to begin with ?..) or use strain gauges and recording instruments for a complete recording of its strains (guess complete world class equipment should cost about 100.000$. You should need about 2 to 4 times this amount if you also need the engineers to do the actual recordings...).
    Conclusion : I guess that the building of good #1900 racing boats did attract a huge amount of talent and energy from many very decent people of the days. I understand that carbon-copies of those boats are not completely satisfactory for different reasons (including the respect of modern safety rules, whatever we might think of the logics which preclude some of them...). Question: do you believe that one guy who might want, in the future (say 2104), to "improve" a 2004-vintage F-17 or Falcon-5000 will have enough command on the work of our best contemporary aircraft engineers, on his spare time, just because he can use the pile of litterature that will be written between 2004 and 2104 ?


    regards
     
  10. FAST FRED
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    FAST FRED Senior Member

    Most rigs are NEVER designed to simply handle the loads , as fatigue must be considered.

    Dry sailing perhaps a tiny safty margin is acceptable , but a real boat kept on a mooring will go thru the stress of 24/7 365 X 15 of small motion which do add to the fatigue factor.

    Most boats I have worked with for offshore work attempt to have at least wire 2 failures per side , and keep the stick in.

    Simply use the vessels displacement as the breaking streignth requirement for EACH stay and you will probably keep the stick for years of offshore work.

    Day boats can use what ever force it takes to flatten the boat on its side with some safty.

    FAST FRED
     
  11. SeaDrive
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    SeaDrive Senior Member

    I believe that I read the the big New Zealand America's Cup boat (the one that raced the catamaran) sailed for several months with strain guages on all the rigging. So maybe someone (Farr?) has a good handle on this but keeps it as a professional secret.

    I'm sure other boats have sailed with fully instrumented rigs as well.
     
  12. Lda
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    Lda Junior Member

    Electronic strain measurement has been used for aicraft development at least since the 50' or 60', I guess that there are no more secrets in those technics. Furthermore I understand that corresponding equipment and services are freely available for sale at a number of respectable companies (a friend of mine worked in that stuff...). Point is those guy usually sell to the like of Boeing or Martin-Marietta and I understand that they just can not provide equipment or services for less than 100 grants because of their own costs. This should not be a real issue for most DOD suppliers or AC contenders.

    Nowaday, due to the rise of Internet and associated technics you might also be able to buy "off the shelf" strain gauges and interfaces and integrate this yourself to your favorite system for a notably lower price, provided you have the corresponding expertises. Corresponding expertise means being educated enough in electronics and computer sciences to be able to qualify succesfully to a high level engineering job at one of the non-forementioned providers, not counting classic mechanics and naval engineering expertises which you also need to make any sense of those mesures.

    I guess that you won't find that many "secrets" in computer analysis as well. At least when speaking of the kind of technics used and the capability to buy some of the like on the market. The secret is more tied to the understanding of the respectives qualities of the different product that might be used and to the experience needed in their use to be competitive, say, in the AC. Plus, I understand that there might be a few advanced stuffs in that field that might be not available today on the market, at least at some of the most advanced AC syndicates.

    Last and not least, saying that most pieces of the puzzle can be bought on the open market, and that you can freely hire people to provide most of the needed expertises does not mean that it comes cheap.
     
  13. guest

    guest Guest

    The big issue as I see it here concerning the strength of rigging elements is not the loads that are in the rig under normal conditions. What causes a rig to fail are the unexpected, impossible to design for events and fatigue; the crash gybe following a broach, the knockdown when a large wave breaks and the boat surfs backwards down the wave. The fatigue of sitting on a mooring doing nothing can be hell on fittings. If a boat rocks from side to side every three seconds constantly for 5 years the rigging will have suffered greater than 50,000,000 cycles. The acceptable stress for a high strength stainless steel at this number of cycles might only be a third of the yield stress for a single cycle. Throw in a bit of corrosion and who knows…

    The point is that to try to refine a design by analysis of a static case could lead to a situation where there is a loading that far exceeds the design case. It follows then that it does not make sense to do this analysis unless the extremes can be eliminated. Eg AC boats.

    What is a more relevant question is the investigation into the stiffness of a rig and how it responds to a gust…
     
  14. tonypearce
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    tonypearce Junior Member

    try "pierre gutelle", volume II, if you want to see how sail loads affect the rig design.
    I have a translation, from the french, of the appropriate chapter.
     

  15. brian eiland
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    brian eiland Senior Member

    Rig Discussion translation

    I would be very interested to see this discussion in english. Can you send me a copy of this translated chapter for which I can pay you. You might also add some of the significant portions to this forum discussion as a PDF attachment?
     
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