Fiber Orientation

By now every boat builder knows that fiber orientation is critical to laminate strength.  And I’m sure everybody knows that 34 oz triaxial for example has a bending strength of some 65,000 psi in the 0 degree, and about 20,000 psi in the 90 degree orientation, hand layup. And unidirectional fabric will have some 100,000 psi bending in the 0 degree and maybe 3,000 psi in the 90 degree.

But that is not all there is to it.  There has to be off axis fiber even if it performs less well.  I first learned about that in Tsai’s composites class in ’90 I think it was.  In tension it would not matter, but in compression and bending, the hard-working 0 degree fibers have to be kept in column, as it were.  The trick is to  have no more than 3 zero degree layers stacked before adding an off axis one.  Then you can add three more.

I have visited mulithull build sites where I have seen plans from famous designers with like, 10 or 20 layers of 0 degree stacked up, and no off axis fibers.  Don’t they know?  And they charge many times what I do.

3 thoughts on “Fiber Orientation”

  1. My late friend allways told me to use diagonal fibers. He was an expert with kevlar explosion proof shells for overseas …
    We used marine plywoods that were 90 deg fibers, 1/2-5/8 and added 45 deg fiberglass tapes for the ends and all reinforcements.
    Worked just fine for many years. Now they use all fiberglass and they need to repair (i find more often) every time they hit a rock.
    I looked at the hulls and they are made differently compared to my Crisscraft . Hand layed …
    The new design i plan to do will have axial glass on the outside and inside of the 3/8″ (3 x 3mm okoume ply) skin. The bulkeads are 2 feets apart and ribs 1 ft apart. I am considering bending a 1/8″ polycarbonate (Lexan) solid sheet epoxied under the inwater skin for low tide skimming. We know where the rocks are but … even with my rabbits poles ahead, a distraction will occur … this is also why the 60 ft hulls will be made in 3 parts (12′, 30′ 18′). Containerable …
    One friend wants me to look at his BIY trimaran with carbon and corecell … i am not too keen at working with composites, would they age well ? on an island, can i find or repair easily ? my bed frame (undermattress) can be made of spare okoume plys …

    1. Oh Oh, a little knowledge can be dangerous. Key to define the mission. Explosions may need 45 degree. You are not designing for explosions but for global loads. Think about global loads again for your container hull. Composites age well if designed right, and the UV is kept away. Who is your designer? Let your designer do the laminate work for your conditions. You would be amazed how much information we collect.

  2. Don’t drive under the viaduct, the columns are built the same way. lots of virts but no horizontal bands around them. Remember the California earthquake? Freeway columns failed because of no horz, same design.

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