Designing a 9 meter sailing catamaran

Discussion in 'Boat Design' started by Pammie, Jul 25, 2018.

  1. Ad Hoc
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    Ad Hoc Naval Architect

    This suggests to me, that you are uncertain in how you have defined your panel aspect ratios...and thus your structural arrangement.
    Would that be correct?

    Thus, let's make sure your panel sizes reflect the structural arrangement to ensure you've not misunderstood. Can you post a sketch of your arrangement - with Dims?

    EDIT - for ref:
    If you imagine an I-Beam. The flanges take the tensile and compression loads, and the web, takes the shear load. Thus the web is the core, which is the foam core, and this must transmit the shear loads. That's it - simple.

    You can find a simplified discussion of this here
     
    Last edited: Jul 30, 2018
  2. TANSL
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    TANSL Senior Member

    Yes, you're right. ISO, in that and in many other things, is not clear enough. If you consider a "natural accident" as a reinforcement, you have to show that its resistant module, its shear stress area and its slenderness are the adequate for a reinforcement in that position in the hull. It is normal to have to proceed to put additional local layers (overlaps) to get the necessary properties.
     
  3. Pammie
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    Pammie Senior Member

    @Ad Hoc: well maybe I wasn't quite sure. But after studying figure 9 I am sure that I did what is intended. See added picture of the front half of the hull which contains the most shear loaded plate. My data was in spreadsheet. Visualising it was a good exercise.
    Good explanation of shear flow; thanks.

    @TANSL: I didn't realise that. Will have a look at it when I start with section 11.
     

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  4. Ad Hoc
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    Ad Hoc Naval Architect

    Ok..well, i see some transverse sections...but...what about longitudinal?
    Since how far do these sides and bottom extend before they are supported themselves?

    How are you taking out the shear load, from the mast?
     
  5. rxcomposite
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    rxcomposite Senior Member

    There seems to be something lacking or wrong diagram in fig 9 of ISO. If the angle formed by the 50 degree base angle and the sides is less than 150 degree, it becomes a 2 distinctive span as diagrammed by the chord line. Yet it is marked as b1, same as illustration a. Anybody care to comment?
     

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  6. Pammie
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    Pammie Senior Member

    The longitudinal distance between sections is given below the sections. My earlier sketch shows a longitudinal stiffener mainly 92 mm above waterline. This extends from x=880 to 7500 mm. In the middle the ring frames are asymmetric because of daggerboard case and have two longitudinal stiffener. Will try to post that later.

    Hmm: the text in the picture says "Most shear load" not Mast shear load :). Not very clear indeed. So is shear load of water pressure. I called it shear load as representation of minimal thickness.
     
  7. Pammie
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    Pammie Senior Member

    You mean the angle in the bottom is also bigger than 130 degrees?
     
  8. rxcomposite
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    rxcomposite Senior Member

    Still need another explanation. 9.12 says" upload_2018-7-31_14-37-18.png
    so for a 10 meter boat, 330 x 10 = 3,300 mm., the longest length allowed for a longitudinal?
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    It is simple enough actually.

    If you were to consider a normal span of a straight beam, between 2 supports, it is L = distance between the two supports., Simple enough.

    Suppose now half way along the beam is bent, let's say at 90 degrees, to form an " L " shape. The span is no longer L, it is L/2. Because half way along the length the beam changes direction and is out-of-plane. The vertical loads imposed on the span between 0 and L/2 cannot bend the beam from L/2 to L. As it is at 90 degrees to it. This at this change of direction this is considered the "support" for the beam of length L/2.

    So if we increase this 90 degree angle to say 100 degrees, is the same still valid - yes! But what about at 180 degrees, i.e it is now horizontal, the span is now back to L. So somewhere between the two is the crossover of whether the span is taken as L/2 or L. And it occurs when the angle at the knuckle (or joint) is 150 degree or greater.

    Does that make sense?
     
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  10. TANSL
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    TANSL Senior Member

    NO.
    The sections 9.1.4.3, 9.1.5 and 9.1.6 of ISO 1225-5 are quite enlightening. and, however you define a natural reinforcement, it must comply with the requirements of chapter 11 regarding reinforcements.
    The only thing that the ISO says is that chines forming an angle between 130º and 150º generally comply with the previous condition. It does not say that with other angles the requirements can not be met.
     
    Last edited: Jul 31, 2018
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Oh dear...that sounds awfully like:

    :eek::p

    Not exactly...it is just saying not taken more than. So if there is any benefit from being greater, non is given or allowed.
     
  12. rxcomposite
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    rxcomposite Senior Member

    Thanks AH. So given the max length, the Alpha Beta EAR rule takes over. The aspect ratio correction factor. More rules in Table H3.
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    Yes, because for that EAR you have :

    upload_2018-8-1_11-34-33.png

    But with the caveat, not greater than, or l >...hence the limiting factor.
     
  14. Pammie
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    Pammie Senior Member

    As promised the sketch of the aft part plate dimensions
     

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  15. Ad Hoc
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    Ad Hoc Naval Architect

    Hi Pammie

    A tad confused.
    Your sketch shows 6 transverse frames, yet you seem to indicate 7 ordinates.
    So which frame is which coordinate?
     
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