Dave Gerr's Lindsay Lord scantling rules

Discussion in 'Materials' started by sinjin, Jan 20, 2016.

  1. sinjin
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    sinjin Junior Member

    I'm trying to identify currently available materials that could be adapted to Lindsay Lord's building technique, as described in Gerr's book "Elements of Boat Strength". The two materials Gerr identifies in his book for this are Dynel and "Vectra".

    I had no trouble finding information about Dynel and Modacrylic fiber, but I'm not sure there is a source of this type of cloth that I can buy in the small quantities I require. I've found products from a few online suppliers that they're calling "Dynel", but I'm not confident that they are, in fact, made from modacrylic fiber. One such site even defined "Dynel" as cloth woven from polyester! Does anyone know of a supplier selling cloth made from modacrylic fiber?

    The closest thing I can find to "Vectra" is "Vectran", an LCP fiber manufactured by Kuraray. Does anyone know for sure what material Gerr was referring to here?

    I have also considered polyester/Dacron, but apparently this material is often used as a peel-ply. Is this because polyester inherently creates weak bonds with epoxy, or must it be coated with something to make it work well as a peel ply? Aircraft Spruce bills it's Dacron cloth as good for use as a peel-ply, but doesn't mention any coating or finish.

    Any suggestions for a presently available woven cloth that would be a good alternative to "Vectra" or Dynel as a reinforecement for epoxy?
     
  2. PAR
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    PAR Yacht Designer/Builder

    You are misunderstanding the use of these abrasion resistance fabrics (Dynel, Xynole, Vectra, etc.) Vectra is a modacrylic and a common use is in automotive airbag covers, also in high end sail fabrics. It's usually woven with other stuff, like polyester to protect the fibers. Dynel is also a modacrylic, while Xynole is a polyester. The chemical makeup of these fabrics isn't as important, as the physical properties they bring to a laminate. More importantly is understanding the way the Lord method works, so it can be engineered successfully. I use a modified Lord method frequently in some of my designs.

    Maybe it would be easier for you to tell us what you're trying to do specifically, as researching material properties is one of the primary tasks for engineering laminates. The Lord method requires a great deal of laminate engineering, if you're going to take advantage of it's abilities. Using Geer's scantlings, will generate a heavy Lord method build.
     
  3. sinjin
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    sinjin Junior Member

    I'm trying to determine what materials, which I can source today, I would use if I built a boat using this approach. Gerr's scantlings for this method of building are quite specific, but I'm not sure I can buy either of the fiber reinforcements he specifies in the quantities I would need.

    I'm reasonably clear on what the Dynel once manufactured by Union Carbide is; however, I'm not sure I can currently buy it, or an equivalent. My research has made me suspicious that at least some suppliers are selling polyester using this name.

    The other alternative Gerr specifies is "Vectra". I cannot find any woven cloth sold under this name. I did find an old post on this forum that indicated that Vectra was polypropylene. If anyone here knows the nature and/or history of this material, please enlighten me.

    I don't thing the present day "Vectran" is what Gerr was talking about, but I could be wrong. He's very clear that the two fibers specified are appropriate for this technique because they stretch under impact much more than glass or kevlar or carbon (i.e., low-intermediate modulus, high elongation). Vectran is a high modulus fiber with an elongation similar to Kevlar.
     
  4. sinjin
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    sinjin Junior Member

    PAR,

    Just noticed you indicated that Vectra was a modacrylic. Do you know who manufactures it or where it can be purchased?
     
  5. mudsailor
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    mudsailor Junior Member

    You can buy Dynel from defender industries in NY www.defender.com

    Sold by the yard, 60" wide
     
  6. sinjin
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    sinjin Junior Member

    See this description of dynel. They're describing something that sounds like dynel to me, but they keep calling it woven polyester.

    Re: polyester/xynole/dacron: I was evaluating it as a possible alternative to dynel and vectra (whatever that is). My concern is that I've found it recommended for use as peel-ply, presumably because it does not form strong bonds with epoxy. The page I linked above indicates that polyester peel ply is treated so that it won't bond to the resin. Any wisdom on the use of polyester with epoxy? More specifically, does dacron bond well with epoxy?
     
  7. sinjin
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    sinjin Junior Member

    Thanks, Mud Sailor. I just sent them an inquiry about what that product is made from.

    I also recently discovered Diolen... characterized as "high modulus polyester". Popular for Kayaks. Seems to be easily obtained in Europe. Anyone here familiar with it? Anyone know where to buy it in the US?
     
  8. moTthediesel
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    moTthediesel Junior Member

    If peel strength is your concern with Xynole, due to the fact that it is a polyester, you needn't worry. I have used it myself many times with epoxy resin, and it's peel resistance is very high. It's also very nice to work with, it wets out very well and does not tend to "float" in the resin.

    You might want to look up some of the testing that Tom Lathrop at Bluejacket boats has done. Also, Reuel Parker has written extensively about the use of Xynole in boatbuilding.

    Tom
     
  9. redreuben
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    redreuben redreuben


  10. PAR
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    PAR Yacht Designer/Builder

    That Ocean Kayaks site has been around for a long time and is full of assumptions and unsubstantiated "results". An example is their results are the same between Dynel and Xynole, but my testing, several others testing and industry testing show something quite different. Xynole is twice as good at resistance over Dynel and nearly 3 times the peel strength over Dynel, by our testing. Simply put this guy's (my assumption) testing is shaded for the kayaker, so they can't recommend these fabrics, if only for the weight they'll bring to a kayak project. Without objectivity, these tests are useless. In the context of a kayak build, some merit, but a qualifier of some sort, at the beginning of the analysis, would have been appropriate.
     
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