biaxial vs woven rovin fibreglass

Discussion in 'Fiberglass and Composite Boat Building' started by busumark, Dec 25, 2008.

  1. busumark
    Joined: Dec 2008
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    busumark Junior Member

    hi, i would like to know which is the best material to use to build a 14ft boat. biaxial or woven rovin mats? what are the advantages of one over the otherone? thanks
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Depends.. If you want clear "wooden" finnish woven is the way. Biax is sructurally stronger. With an avarage 14 footer there's not major drawbacks with either one..
     
  3. busumark
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    busumark Junior Member

    thanks for reply. with wooden finish what do you mean exactly because i was told that with biax the boat is more smooth and with woven there are some places that you can see the squares of the mat against the light
     
  4. TeddyDiver
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    TeddyDiver Gollywobbler

    With biax there's bigger risk having litte air trapped btw the fibers during the process producing a bit "cloudy" appereance. Biaxials have also the additional stitching to bind the fabric. The squares with woven will disappear with additional layers of resin.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Teddy's right, you have it backwards Busumark. The biax produces a much rougher surface, requiring considerably more effort to fair smooth. Woven fabrics "wetout" cleanly, lay down flat and if a light enough cloth is used, it will become completely transparent. There is no "mat" in regular cloths. Now there are "combo" fabrics, where a mat is lightly stitched or bonded to a layer of mat, but this is a bulking product used to increase laminate thickness and not something that would be used in a clear coat application or with epoxy.

    I would help to know which 14' boat you're building. Generally on a taped seam build of this size I'd use 8 ounce biax on the centerline and chine seams, then (after fairing) sheath the full exterior of the hull with a 6 or 8 ounce cloth. This would provide 16 or so ounces of material on the chines and centerline seams, with a 8 ounce fabric everywhere else for abrasion resistance and water proofing.

    Technically, you could use just 8 ounce cloth (tape) on the seams, but I'd be inclined to use at least two layers to gain strength. This is an extra step compared the method I previously described and not as strong, so hence my choice for biax seams and regular cloth fabric sheathing.

    If you want the wood grain to show (clear finish) then you can't use biax or cloth weights heavier then 4 ounces. 6 ounce cloth is just barely visible, but it's there. 4 ounce cloth is all but invisible once the weave is filled with additional coats of resin.

    If this is a plywood build, epoxy is the choice. Some have used other resins (polyester and vinylester), but results will be less water proof then epoxy and the poly's are more difficult to work with, if you're not accustomed to them.
     
  6. sabahcat
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    sabahcat Senior Member

    Stitched is even better sitting flatter than all and as the fibers arent going over and under, but run straight, the loads pull straight and I believe you get more strength for less weight of cloth.

    I'd suggest a double bias cloth
     
  7. busumark
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    busumark Junior Member

    the boat is going to be built from a female mould. all the boats that i have seen have been made with woven and in some places you can see the squares against the light but i havent seen one made using biaxial so i havent seen a finished boat with this material. my question is more how the boat looks like than a question of strenght.
     
  8. TeddyDiver
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    TeddyDiver Gollywobbler

    You absolutely right.. but the strength and resin/fiber ratio isn't an issue with avarage 14 footer, neither the price of the fabric. It's totally different with 14' cruising cat :D
     
  9. PAR
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    PAR Yacht Designer/Builder

    A few things need to be ironed out before you decide on your fabric schedule (which has to be engineered). If building inside a mold, then it sounds like you'll be using either polyester or vinylester. If this is the case, vinylester can take advantage of biax fabrics, but if polyester, you're just wasting fabric, because the resin doesn't have the elasticity to compete with the stronger fabric, regular woven is fine. In both cases, you'll want mat in the laminate, for bulk and to prevent "print through" which is as you've previously described as "squares showing through". Properly applied, placed and correctly sized, mat will prevent print through.

    On the other hand, if you're employing epoxy as your resin, then you can skip the mat all together. Weave filling and fairing coats will prevent print through. Secondly, the resin is much stronger, more water proof and take full advantage of the higher modulus fabrics (like biax), because the elasticity of the fabric matches that of the resin.

    I can think of several locations on a 14' boat, where having the additional strength of biax or other high modulus fabric can be beneficial. Not only for load bearing but to help produce a lighter, stronger structure.

    It would be very helpful to let us know what you're building, the designer, model, etc. With this, the discussion can go from generic and general guidelines to specific recommendations for your application.

    With the basic nature of you questions so far, I hope you're not trying to develop a laminate schedule yourself. Thermoset plastics (fiberglass resins) and the reinforcements (fillers, fabrics, mats, combos, etc.) used in them require a fair amount of understanding or you'll end up with overly heavy and or weak structures. A set of plans may seem pretty simple, but lots of expertise usually goes into them. The better designer's work (drawings) look satisfyingly simple, but in fact are highly engineered and refined. This is the hallmark of a good designer.
     

  10. busumark
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    busumark Junior Member

    no i am not going to built the boat myself. there is a boat builder and he told me that he does his boats with biaxial not like the other boatbuilders that use woven. he told me that his boats are stronger and have a smooth finish.he told me that they use it tp build powerboats and that it is more expensive. i asked these questions because i dont trust this person. he doesnt even know the correct name of the material i had to check it on the net and wanted to know some things about this material because i have never heard about it.
     
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