Hull thickness requirements different materials

Discussion in 'Fiberglass and Composite Boat Building' started by Gasdok, Jan 21, 2023.

  1. Gasdok
    Joined: May 2020
    Posts: 24
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    Location: Florida

    Gasdok Junior Member

    Looked at Gerr's scantling system gives hull thickness as LOA/ 1000.
    A 30 FT boat would require .0.36 inches plus 15 % for bottom plus 10 percent for a planing hull for a bottom thickness of
    0.45 inches.
    I am assuming this is with a mat/roving layup. I am planning a 1700 biax vac infused build probably with a core. Will the different materials allow a thinner layup?
     
  2. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    The thickness, by itself, does not guarantee anything. Furthermore, for a certain type of ship, for the bottom panels, for example, the material needed may be totally different in the middle of the hull than in the bow area, or in the keel than near the waterline.
    You can put a laminate of enormous thickness that, at worst, does not meet the recommended minimums. An analysis of the existing stresses through the thickness of a laminate should always be carried out to verify that each and every one of the layers is working correctly. This will allow the designer to adopt the minimum weight combination while giving him data to see if it is convenient or not to use a sandwich type laminate.
    The recipes that were used 30 or 40 years ago are no longer useful, the calculations have become more rigorous, more technical, which allows for much more optimized structures, whether you are looking for weight savings or if what you want is to save on labour.
    Consider layering multiple mats or fabrics on top of each other to make up your laminate. Don't go for just one type, 1700 biax for example. Place weaker materials in layers near the neutral axis and stronger materials in the outer layers. This facilitates lamination and reduces weight and material cost.
     
    fallguy and bajansailor like this.
  3. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    @Gasdok can you tell us a bit more about this 30' boat which you are planning to build please?
    What type is she - it sounds like she will be a planing sportsfishing boat type?
    Do you have a design in mind, or are you designing her yourself?
    If the latter, how far have you got with the design so far? Can you post any sketches?

    Dave Gerr's scantling formula is very generalised, and as Tansl says, you can optimise your scantlings in different areas.
     
  4. Gasdok
    Joined: May 2020
    Posts: 24
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    Location: Florida

    Gasdok Junior Member

    Planing stepped hull catamaran. Ventilated steps
     

    Attached Files:

  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Build a plug and test it; then build a mold after refining it.

    The laminate is the least of the worries unless a proven hull.
     

  6. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    Brutal question-have you ever built a boat before?I'm afraid I'm not seeing anything that looks close to ready for calculating hull laminate specs.The best idea is to go with what an experienced designer calculates.The alternative is not to venture into water much more than waist deep.
     
    TANSL, rxcomposite and fallguy like this.
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