How valid is Marchaj area under the stability curve for catamarans?

Discussion in 'Stability' started by UpOnStands, Oct 10, 2017.

  1. Ad Hoc
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    Ad Hoc Naval Architect

    Unfortunately there is a real need. Since the answer to my question, which you have still yet to answer, dictates the reply I give you. And thus your understanding.
     
  2. UpOnStands
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    UpOnStands Senior Member

    No denying my lack of experience or indeed understanding. So the formal answer is no, I have never done a stability calculation.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Buoyancy is not dependent on depth of immersion.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    which brings me to this (and my point)

    If you think of a simple box that is floating and is connected to another equally simple box by a raft section. Thus forming a multihull. Let's says the draft is 1.0m at rest. And let's say the displacement of the whole boat is say 10 tonne on this 1.0m draft. Ok with this?

    Fine...so the whole vessel is now heeling, let's say due to a wind force. This means the hulls will rotate. For the sake of simplicity (as the reality is not) let's say it rotates about the vessel centreline...ok?

    So if the whole vessel/boat keeps rotating until one of the box hulls is out of the water...does the boat weigh more or less or the same as before the wind force was applied?

    Obviously it is the same, since NOTHING has changed or been added or removed on the boat.

    Thus the single box hull that is now left in the water, while the other is now in the air, does this single box hull remain floating on an equivalent 1.0m draft or must it now accommodate the total displacement of the boat?
     
  5. UpOnStands
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    UpOnStands Senior Member

    will reply when time permits
     
  6. UpOnStands
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    UpOnStands Senior Member

    Ok, as the sail inclines off vertical the wind hits the sail obliquely imposing a horizontal load and a vertical load?
     
    Last edited: Oct 11, 2017
  7. Ad Hoc
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    Ad Hoc Naval Architect

    The question is thus:

    Nothing to do with:
     
  8. UpOnStands
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    UpOnStands Senior Member

    Replying to your
    Doesn't the wind needed to rotate the boat also increase the load on the boat?
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    So the wind, a horizontal load, increases the weight, a vertical load, of a boat??
     
  10. UpOnStands
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    UpOnStands Senior Member

    Yes, through the oblique surface of the sail.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    So....that's a no then.
    You don't understand the question then. Discussing a non sequitur does not aid you either...
     
  12. UpOnStands
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    UpOnStands Senior Member

  13. TANSL
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    TANSL Senior Member

    Yes, imo, stays, shrouds, etc. transmit compression loads to the mast.
     
  14. Ad Hoc
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    Ad Hoc Naval Architect

    Aahh..ok....so that's a no then, again. You can't or are unable to answer the question i asked above.
     

  15. UpOnStands
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    UpOnStands Senior Member

    Which question?
    has been answered. YES
    If the force that rotates the vessel is wind acting on the sail the answer is that the vessel's displacement is increased. If the wind stops the additional load vanishes.
    answer: Assuming equilibrium and no external forces the immersed box(hull) must carry total weight of vessel .

    Anything missed?
     
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