Need scantling for 17m motor yacht in ISO SCT or Hullscant will pay for it

Discussion in 'Class Societies' started by linda.vrdoljak, Feb 2, 2015.

  1. rxcomposite
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    rxcomposite Senior Member

    Experience will tell you that 900gr/m2 is too heavy to drape and layup. Find the weight that will drape well in the top/cap and radius well in the base/tabbing area. You may find two types of fabric will be practical for small and large stiffeners. Stay away from CSM in frames and stiffeners. Use biax or WR and use uni on caps whenever practical.

    I usually use DBM450 and seal it off with CSM300. The caps are overlapped to gain bulk or better yet, fill it up with uni fibers. Unis have almost 3x the strength of WR. I am sure SCT software can handle the calcs.

    Use the suggested tophat profile of ISO. It is there for a purpose.
     
  2. rxcomposite
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    rxcomposite Senior Member

    I'd go for 12mm bottom at midship. 9mm is too thin.

    Chines/strakes/sharp bends are usually 1.5x the bottom laminate thickness. Check ISO rules. It is usually fiiled up with compliant resin to ease up the radius. Me, I use roving strands to fill up radiuses.

    Again, I highly suggest you review LR SSC chapter on Construction Details. The details is what separates a good boatbuilder from a sloppy one.
     
  3. linda.vrdoljak
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    linda.vrdoljak Junior Member

    re

    You all suggested ask you arhitect, here she is.

    Epoxy filler and ceramic sanding disc gave even surface.
     

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  4. daiquiri
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    daiquiri Engineering and Design

    Very classy typo, I have to say. :D

    If it is also revealing your musical taste, you have my compliments. ;)
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    I am coming to this thread very late, not read it all either.

    Have you got what you initially asked for?
     
  6. linda.vrdoljak
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    linda.vrdoljak Junior Member

    Q

    scantling (stress analysis per ply- good one, not thickness)

    Should it be in El-c or El-b (iso materials)

    I know when I spoke with Imci they ask for laminate test EL-a, but I need something to start with.


    Some members here said they go by El-b and never had single problem, even when compaing to Abs offshore racing, numbers came very simmilar, sould I follow the same route?


    Finaly I got my plans straight, before was mess with uneven panels was just time and trouble,
    Now bottom and side panles same length, layout fits, all walls are bulkheads and lay on hull stiffeners. Now is simphony. Aspect ratio over 2:1 all good stuff.
     
    Last edited: May 7, 2015
  7. linda.vrdoljak
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    linda.vrdoljak Junior Member

  8. linda.vrdoljak
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    linda.vrdoljak Junior Member

    q

    what is minimum depth to becomae natural stiffener?

    I have 3.5cm here
     

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  9. TANSL
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    TANSL Senior Member

    Like any other reinforcement, it should have the necessary module, along with its associated plate, to withstand the design pressure in that area.
     
  10. rxcomposite
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    rxcomposite Senior Member

    It is not the depth but the angle. See ISO rule. A hull to deck is a natural stiffener. A transom step is also a natural stiffener.
     

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  11. TANSL
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    TANSL Senior Member

    Indeed, it depends on the angle so that it can be considered a "natural stiifener" but in addition to meeting the requirement of the angle, the standard says it should be "strong and stiff enough to be considered as proper stiffeners" (see first picture of RX). Therefore, in some case, it must be added, for the interior, additional layers of fiber.
     
  12. rxcomposite
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    rxcomposite Senior Member

    It is not stated in ISO rule but in most Class Rule, whenever there is a "sharp bend" such as chine, it should be reinforced by 1.5X the adjacent panel thickness. Thus, it must meet the necessary modulus by being "strong and stiff". This is usually illustrated in the design details but not in the design calculations.

    Correct me if I am wrong, but wasn't there somewhere in ISO where this "bend" is discussed and an equivalent modulus given? Not in ISO 12215-5 but somewhere.
     
  13. TANSL
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    TANSL Senior Member

    Rxcomposite, I think you're right. In this matter, as in several others, the ISO standard does not clarify anything. The designer must use his experience with other classification societies to solve unsolved problems in the ISO.
     
  14. rxcomposite
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    rxcomposite Senior Member

    Thanks TANSL.

    I found something. Still have to understand it but it is near morning our time.
     

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  15. linda.vrdoljak
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    linda.vrdoljak Junior Member

    Re

    You can see how they "skipped" 2 side longitudinals (10cm x 5cm they say is long stiffener and 2x900csm - 4mm)
    And they claim hull to be, no more 45x45cm unsuported panels and using this "natural stiffener"
    7.5kgm3 is hull, side 4kg of fiber

    nothing too impressive on thickness to allow to omit 2 side stiffeners and Lloyd A category boat,
    even in Iso doesnt let me to do 50knots wothout stress and with better (narrow) panel if I use same fiber weight above.

    I cant see how deep is "groove" but I think is bit more than what I have, 3.5cm.

    Ad hoc? What dnv say for this
    ;)
     

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