Alternative to marvelous Buccaneer 24

Discussion in 'Multihulls' started by Gary Baigent, Apr 18, 2010.

  1. cavalier mk2
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    cavalier mk2 Senior Member

    Which leaves the enthused carbon based fans beaming!
     
  2. buzzman
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    buzzman Senior Member

    Are wave piercings the latest facial jewellery fad????

    So not up on this 'modern Jung people stoof'.....
     
  3. cavalier mk2
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    cavalier mk2 Senior Member

    We should all thank Gary for being understanding as we explore the alternative....
     
  4. buzzman
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    buzzman Senior Member

    ...and accentuate the positive.
     
  5. Gary Baigent
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    Gary Baigent Senior Member

    Rebuilt and alterred main asymmetric foils for Groucho are near finished. The vertical sections are new; the old ones broke at the hard point - and there are 10 layers of uni directional carbon each side around the L junction curve and up past the float/foil hard point area - so it is almost solid carbon there. The tips have been altered and the L lifting area is now level - whereas before they angled down at a slight angle - and touched bottom early in shallow water.
     

    Attached Files:

  6. Doug Lord
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    Doug Lord Flight Ready

    Gary, its probably too late to change but if you were to make a bigger radius between the vertical and horizontal it's probable drag would be reduced and they might even start to work like TNZ foils(automatic altitude control).
    Looking pretty good ,though....
     
  7. Gary Baigent
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    Gary Baigent Senior Member

    The radius curve doesn't show in the photographs but it is quite a soft turn - no sharp edges. On Sid where the J foils were built from scratch, the radius is much wider - but couldn't do that with these two ... unless I build completely new. And I'm too lazy. The old foil designs worked fine ... but gave up the ghost under heavy loads. Hoping the thicker carbon on the rebuilds will halt that.
     
  8. P Flados
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    P Flados Senior Member

    Gary,

    You probably know this, but in case other readers do not:

    Along the length of the foil, bending loads go up the closer you get to the contact point at the ama (your hard point). This is easy to understand, and allows a builder to focus on putting reasonable amounts of fiber where it it needed.

    Less obvious is the needed layup distribution on top vs. on bottom.

    The carbon in hand built foils is much stronger in tension than in compression.

    In tension, less than perfect fiber alignment (including the pattern cause by the weave of a fabric) is not as big a deal, the fibers that do pick up the load are very strong and any amount of fiber rearrangement just helps. This is where high stress fibers become more straight which better distributes load.

    In compression, individual fibers or small groups of fibers tend to want to displace in a buckling fashion. As such, high stress fibers tend to get less strong and/or fail.

    For the Groucho foils, the very top of the foil at the thickest point is where failure in compression is most likely to start. This is where something like very carefully placed thick uni is a good choice. In fact, I would recommend putting twice as much primary load orientation fiber on top as you put on the bottom.

    On my small test platform tri, I am confident that all of my foil failures / near failures started with local buckling at the location of max compression as described above.
     
  9. Gary Baigent
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    Gary Baigent Senior Member

    Correct, PFlados, the foils crushed (both carbon and wood core) on the compression side a couple of fingers widths below the float exit area.
    I would have thought another breakage area would have been at the curved L section point (because of similar amounts of carbon layers there) but no problems. As you say, the danger area is the exit. I think I may have overdone the new laminates - but rather that than annoying groaning and breaking sounds ... and then you have to slow down ... and think, "Have I got enough epoxy on board to fix that?"
     
  10. santacruz58
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    santacruz58 Senior Member

    Thankyou P Flados and Gary for your thoughts. It is my understanding limited as it is that when using uni directional fiber that there should be some layers of fibers running across the uni to help bind them together as in your example of fibers under compression. The fibers across bind the individual or groups of fibers and help them from buckling under compression. Is this correct?
    nelson
     
  11. mcm
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    mcm Senior Member

    I'm confused, i understand the top of the foil as the contact point with the ama as opposed to the bottom tip.

    But it sounds like you're saying one face of the foil is in tension, while the other face is in compression.

    Are we talking about the faces or the top and bottom ends ?
     
  12. Gary Baigent
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    Gary Baigent Senior Member

    Yes, my description was not good.
    We're talking about the vertical section of the L shaped foil, the part like a conventional daggerboard, which in my design, is asymmetric (same as the lifting near horizontal foil part) and the foil broke at or close to the top of the vertical section at the float exit. And if the boat, in my case, was overloaded from wind strength and speed, the platform was obviously slipping sideways, making leeway, so the foil crushed on the compression side. And maybe there was so much lift developed from the horizontal L section, that that also contributed to crushing the upper part. The tension side (leeward) also gave way, but was not as ugly to look at as the compressed side. Hope that is clearer. Doesn't read very well though.
     
  13. P Flados
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    P Flados Senior Member

    Bending loads are the dominate concerns. For Gary's foils, the upward loads on the horizontal portion and the side load on the vertical portion combine on the lee foil to produce the max total bending loads. The max total bending load is transferred from the foil into the ama structure. At this location, the inside surface of the vertical foil is in compression for the lee foil. The fibers with the maximum compressive stress are at the surface of the foil at the location of maximum foil thickness.

    I have read a bunch of stuff about how to prevent local buckling.

    I think it may be possible to get fancy with the layup in a couple of ways.

    If the outer fibers are at 45° to the primary stress, they load up at a rate of 0.7 of the axial fibers. They may also add stability to the axial fibers.

    Also, if a you build up 85% of the fiber as normal, and then place the foil under a bending load prior to applying the outermost fiber, you can "transfer" a portion of the bending load away from the surface into fibers away from the surface. This spreads out the load more evenly and again you try to have your highest stress fibers down where they are more supported to prevent local buckling.

    However, the fancy stuff is small change compared to the main item. This is the combination of:

    • Having enough material
    • Having enough section thickness
    • Correct application of the carbon fiber material
     
  14. Marmoset
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    Marmoset Senior Member

    ^---------idiots observation mind you but...


    Possible candidate for light cheap spiral of carbon tow as well? Or double criss cross of tow down the length.


    Barry
     

  15. P Flados
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    P Flados Senior Member

    Tow is all I have used (I focus on low cost). It has advantages and disadvantages. Major amounts of tedious work is probably the biggest downside.
     
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