Composite mast

Discussion in 'Fiberglass and Composite Boat Building' started by denmic, Feb 9, 2020.

  1. denmic
    Joined: Mar 2015
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    Location: South Africa

    denmic New Member

    I am wanting to build a CF mast for a 41' catamaran. The cross section of the mast will be elliptical with dimensions of 385mm x1 75mm and 17.5m long with the top 2m tapering from three sides and have a prebend of 80mm. The process I am considering is as follows:
    1. make and set up female half mold stations.
    2. strip-plank mast mold in two sections with 3mm cedar strips glued together with thickened epoxy. 3. Lay one layer of 420g/m2 45 x 45 assembled roving which will be inside of mast.
    4. Join two halves of strip-planked mast together.
    5. Fair this mandrel and layup over it with carbon fiber and epoxy. (mandrel stays as part of the mast)

    I think about 8-10mm wall thickness is what i would need to achieve with most of the fibers running longitudinally (70-80%) and several layers running at +45 and - 45deg (20-30%). For a hand layup I think using 300gsm uni for all layers would work, pulling the diagonal fibers really tight while wrapping and using peelply and packing tape over every third layer or so.
    My questions are: Is this a feasible idea? and. How many layers of 300gsm CF to make up thickness I would need for such a mast?
     
  2. rxcomposite
    Joined: Jan 2005
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    Location: Philippines

    rxcomposite Senior Member

    You need also 90 degree fiber on the inside. This is the hoop strength and prevents the wall from collapsing. If you are thinking of filament winding the manual way, just pull the uni tight while winding and have someone squeege out the excess. This is the basic principle when winding Uni.

    And you can use a dissolveable mandrel on a pipe. After curing, you dissove the mandrel.
     
  3. denmic
    Joined: Mar 2015
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    Location: South Africa

    denmic New Member

    Thank you rxcomposite, so the first layer over my cedar core should be uni at 90deg for hoop strength.
    Is 300g uni the right way to go for this kind of layup i.e manual filament winding or could I go with 500gsm and how many layers and in what sequence?
     
  4. denmic
    Joined: Mar 2015
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    denmic New Member

    It seems 300gsm is all I can get locally anyway.
     
  5. rxcomposite
    Joined: Jan 2005
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    Location: Philippines

    rxcomposite Senior Member

    Go to a local library and check Filament Winding Composite Structure Fabrication by ST Peters et al before you embark on this very expensive project.
    You don't need to read the whole book as it contains some very advanced calculations. Read only the part how to make different mold for filament winding. You don't need a machine also. Only a rotisserie as long as there are friends to help you.

    The book also gives suggestions on the percentage of layers for hoop, axial, and nearly horizontal windings for thin wall cylinders. The book also tells you how to calculate different thickness/width per weight of the fibers.

    Maybe you will also get some idea on how the fibers are pre wetted before winding.
     
    Last edited: Feb 9, 2020
  6. denmic
    Joined: Mar 2015
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    Location: South Africa

    denmic New Member

    Thank you I'll have a look in our sparse library but I am doubtful I will find it. I'll also check online maybe I get lucky.
     

  7. rxcomposite
    Joined: Jan 2005
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    Likes: 185, Points: 63, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    I bought the book (2nd Edition) for $100 at SAMPE before. Have heard there are many editions later. Very good book. If you immerse yourself in the math, you can do design also.
     
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