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. Alik
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    Alik Senior Member

    ISO does not require any bulkheads and does not consider strength in case for damage. Class rules do need bulkheads, say GL24<, DNV2-21, LR SSC...
     
  2. TANSL
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    TANSL Senior Member

    It is totally wrong to compare the results of any classification society with those obtained with ISO.
    I think Alik has explained it perfectly in post # 13.
     
  3. vkstratis
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    vkstratis Naval Architect

    Agree, but still you will have non-watertight bulkheads which require scantling determination and can be also used as structural elements, thus they have to be calculated.
     
  4. vkstratis
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    vkstratis Naval Architect

    ISO might provide lower results but still 11mm FRP bottom panel for a 17m boat achieving 50knots is too thin from my little experience. Anyway I dont think this is going anywhere since there are no plans provided for any real measurements and calculations.
     
  5. Alik
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    Alik Senior Member

    Yes in this case we take bhds as flat bar stiffeners.
     
  6. TANSL
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    TANSL Senior Member

    I just think it's too thin if calculations with ISO give me a higher value. Never by comparison with the calculation of a workboat with ABS. That, again, is completely wrong.
     
  7. TANSL
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    TANSL Senior Member

    My normal practice is to always stand bulkheads on an existing reinforcement. The forces transmitted by the bulkhead on the hull are spread more evenly and calculating the bottom panel / Side forgetting the existence of the bulkhead.
    I calculate the bulkhead by itself, not because it is a reinforcement of the hull.
    But here, of course, everyone will have their preferences.
     
  8. linda.vrdoljak
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    linda.vrdoljak Junior Member

    Tansl and Alik, this is what I want bulkheads as part of interior walls- the right way, and to be placed on stiffeners, like original Pilot boats but not placed directly on hull skin, it mat show "hungry dog" ribs.

    My Material technitian suggested "core"? for the bottom, and I'm against it all the way. Saveheave Marine also mention "no core hulls" at their yard, its hard to repair and It could delaminate faster.

    His proposal; laminate schedule goes 5 thin layers for face powdered with iso resin, than quadriax 900 w 600 csm to bond it, no "transition" layer from 300>900 biax?, and as many as needed straight forward, but "core" in the middle???

    And my suggestion was something like, 2x300, 2x450 csm, transition layer 600wr, and 1000wr 500csm as may as needed. Gets you stronger laninate with no quadriax, thickness is the same.

    Fist I did sketch to match walls with bulkheads and stiffeners, than we did it in cad

    17mm is easy to get if plate is larger, pilot boat has 14mm @ 35x40 plate size.
    I got 16mm with csm if plate is 70x90, at atf, than narrow it 60x40 and wr-ing it, you get 10-sh mm. Same boat 20tons B, 50 knots.

    Abs scantling is heavy duty stuff like lloyd, at the begining I left pleasure craft comparason iso vs rest of the class rulles to 24m.

    iso "allows" you 10.5mm at aft (12mm @ 2/3 loa) for 17m 20ton for 50 knots, but I'm not going to do this thin. And its nothing worse if you compare sith other CR for pleasure crafts.

    Look at japanesse scantling its even worse.

    Right now I"m comparing numbers, ISO boat is good but GL or RINA = Value.
     
  9. TANSL
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    TANSL Senior Member

    Before thinking about "core" (sandwich), consider using the infusion method and, importantly, the possibility of using the evaluation level "A". These two options reduce the required thickness.
    The thickness aft, I don't know what will be, but no doubt be much lower than at bow areas.
    You will do well to put in each area the thickness required because, in contrary case, you will have a much greater weight than necessary.
    Learn how to save weight. Maybe add an extra stiffener allows you to save weight by getting a smaller thickness for the bottom/side panel.
    In my opinion, you can do several things before using sandwich panels.
    Another issue : ISO can be good or bad but for the CE marking the best you can do is to use the ISO.
     
  10. TANSL
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    TANSL Senior Member

    If this helps: in the calculations I've done, using the "EL-b" instead of "EL-c" would be reduced thickness in 1.5 mm.
     
  11. vkstratis
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    vkstratis Naval Architect

    To be honest, I think you should consult a professional with both experience and qualification. Scantlings calculations can go quite complex and require more than min. thickness calculation, i.e. you will need stiffener placing, section sizing for stiffeners and scantlings determination for everything besides bottom panel. It is a job which cannot be done at forum threads.
     
  12. TANSL
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    TANSL Senior Member

    That is what, for days, we are saying. But besides that, this boat has a special feature, which is 50 knots. What can you say about this?
     
  13. vkstratis
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    vkstratis Naval Architect

    ISO only applies to craft with a maximum speed up to 50 knots in mLDC conditions. So ISO is probably at its boundaries for such a boat.

    Besides scantlings I would first consider if the boat is indeed designed for such speeds, as Alik mentioned earlier. The whole thing is somehow problematic. There no lines, no preliminary scantlings, so no weight schedule and no resistance/propulsion analysis. How does the thread's author know he will do 50 (plus?) knots? He mentions boats like Pershings and offshore boats which are complete different designs and serve different purposes.
     
  14. TANSL
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    TANSL Senior Member

    Yes, you're right, the boat is at the limit of what is regulated by ISO 12215. However, it is always possible to make some preliminary calculations for, among other things, better calculate the weight of the hull. As you know the project spiral occurs because you do some calculations that take you to deduct other things, that force you to correct the initial estimates. So even though you're right, it is necessary to calculate scantlings although missing some data.
    As for how to achieve 50 knots, I fear that the author of the thread does not know that, perhaps, with that hull is not possible. If you read the previous pots you will see that Alik already mentioned this point. If you read the previous posts you will see that we have already said most of what he had to say. But your opinion, the third, help, hope, to linda.vrdoljak follow our advice and you rent the services of a NA.
     

  15. vkstratis
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    vkstratis Naval Architect

    I 've got no reason not to agree with you TANSL.
     
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