Fiberglass and composites applying question

Discussion in 'Boat Design' started by Albert Jr., Sep 29, 2014.

  1. Albert Jr.

    Albert Jr. Previous Member

    Let's say you have a mold for a 17 ft semi-v.
    Nothing special, more for fishing and recreation.
    Requirements;
    - 3 piece construction
    - divinycell foam core
    - can carry an engine of up to 390 lbs (115 e-tec)

    Which layers of fiberglass and how much would you apply to each mold ?
    What should the foam thickness be and which type of divinycell ?
    What should the transom thickness be and what composite should I use (I saw some builders using coosa for their builds)?
    How wide a beam would you prefer ?
    How big should the bildge be ?

    Only looking for opinions and advice.

    Thanks and regards,
    Albert.
     
  2. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    Well, lets see...
    Find a finished boat out of the mold, cut some holes in the boat with a sharp 2" holsaw and sand the cut edge until you can "read" the laminate schedule.
    OK, really, the answer to almost all your questions is, "well, it depends..."
    So post up lots of accurate information and some clear photos from every imaginable angle, then ask again!
     
  3. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Albert - you don't seem familiar with the engineering of a boat hull.

    Just by coincidence, I came across this set of calculations for a 28ft boat today (attached) .

    Once you have figured out the pressures on the hull from operational loads, THEN you can consult a qualified professional to design the hull to carry the loads, and the appropriate Dvynilcell stiffness ( at least 4 common choices) and the Fabric design ( at least a dozen common weights and weaves ) to suit.

    17ft is big enough to get you into real trouble trying to guess the right answer, especially if you expect to insure the craft, and carry a crew into fairly rough waters - where, like now, its easy to find yourself in over your head.
     

    Attached Files:

  4. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    The ISO 12215-5 standard for pleasure boats, in case of fiber reinforced plastics, requires not only a minimum thickness in each zone but also in the case of non homogeneous materials, requires a study of stress distribution in each one of the layers making up the laminate. This results in that while the total thickness may be sufficient, the stress on any layer may exceed the maximum permissible value for the material whereby the laminate is invalid.
    Therefore, make a hole in the hull to take a sample, is useless as it is impossible to know the composition of the laminate. The only thing you can find is the thickness and % fiber, all of which is not enough.
    If you want to do something rigorous, or are required to comply with the ISO standard, in addition to the calculation of pressures, as well rwatson says, you need take into account considerations a little more complicated.
     
  5. Albert Jr.

    Albert Jr. Previous Member

    Thankyou for the reply, do you know where I can find the ISO standard ?
    I'm not sure if it's needed at Curacao but I'm interested in knowing what
    standards are really used and needed.
     
  6. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

  7. Albert Jr.

    Albert Jr. Previous Member

  8. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Obviously, if you are using a mould, the beam is not changeable and I don't understand your enquiry about the bilge. Unless there is some requirement to keep the boat's weight within strict limits, you might be better not using the core.
     
  9. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    The only standards you really need are the ones the insurance companies and boat registration authorities recognize.

    Contact them in your operational area, and /or your local marine authority for advice.
     

  10. Albert Jr.

    Albert Jr. Previous Member

    Thanks guys.
     
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