drag calculations for large catamaran

Discussion in 'Boat Design' started by fredscat, Oct 2, 2010.

  1. Ad Hoc
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    Ad Hoc Naval Architect

    So, if you have completed "some preliminary design", can you show the GA and give a summary of the SOR?
     
  2. Leo Lazauskas
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    Leo Lazauskas Senior Member

    The good news: you can use the free program "Michlet" to estimate the calm-water hydrodynamic resistance including the interference. (Note: in hydrodynamics we use the term "resistance" not "drag".)

    The bad news: it is only a very small fraction of the work you need to do to get estimates in a real seaway.

    The best news: you have received excellent advice, especially from Mike Johns and Ad Hoc.

    Good luck!
    Leo.
     
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  3. fredscat
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    fredscat Junior Member

    Thanks, I do agree on having received excellent advise and I am thankful
     
  4. fredscat
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    fredscat Junior Member

    The hulls are a fiberglass - PVC foam _ fiberglass sandwich. All the loads are transmitted into the inside skin area via bulkheads and ribs and stiffeners. The panel stiffness is provided by the sandwich construction.
     
  5. fredscat
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    fredscat Junior Member

    I can / and will provide the General Arrangement structurally speaking If by SOR you mean the parameters of the design philosophy, as in expected performance, displacement, draft etc. I will do so as well. I am new to forums and I am not sure on where or how to post this information. May I or should I send it to you via e-mail?
    I see you are a Naval Architect, do you have FEA capabilities? if so, in what form would I have to submit the drawings to go into ALGOR or similar software?

    I have all my "STUFF" in 3D AUTOCAD but designed for shop use not for FEA.
     
  6. fredscat
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    fredscat Junior Member

    I can / and will provide the General Arrangement structurally speaking If by SOR you mean the parameters of the design philosophy, as in expected performance, displacement, draft etc. I will do so as well. I am new to forums and I am not sure on where or how to post this information. May I or should I send it to you via e-mail?
    I see you are a Naval Architect, do you have FEA capabilities? if so, in what form would I have to submit the drawings to go into ALGOR or similar software?

    I have all my "STUFF" in 3D AUTOCAD but designed for shop use not for FEA.
     
  7. apex1

    apex1 Guest

    It would be fine to post it here and not behind the curtain (e-mail).

    One of the reasons of these threads are, to let other members gain knowledge not just one.

    Regards
    Richard
     
  8. fredscat
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    fredscat Junior Member

    thanks for the clarification
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    You can post here, or send me a PM with your email address, it is up to you. You don't need to post everything and in fine detail too. Just the main GA, which identifies the layout and what is where. Same for the SOR, ours are some 30+ pages long...but you can summarise in one page the main aspects of what the design is for and its intended operation.

    I am also surprised by your statement of "inner skins".

    The whole purpose of using a sandwich construction is to increase the stiffness of the member. Thus both skins are working. If you are relying on just the inner skin, this is a skin skin construction by the back door, which doesn't make sense in the approach and methodology???? Hence the GA and SOR will shed light on what you're trying to achieve.

    Yes, i do have and use FEA.
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    BTW....FEA is a tool, just a tool. Not every project requires a full FEA. It also depends upon the purpose, ie what the output is going to show you and what will you do with said data?

    Hand calculations can provide over 90% of the structural design of a multihull. I use FE as and when i need to either support my hand calculations, to obtains SCF especially for fatigue analysis or, some calculations would simply take too long by hand as too complex.

    Don't get fooled by the pretty colours and animations....it is just a tool, and a sleeping beast if not used properly.
     
  11. mydauphin
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    mydauphin Senior Member

    Guys speak English so others that are not so studied know what you are speaking about...
     
  12. latestarter
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    latestarter Senior Member

  13. mydauphin
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    mydauphin Senior Member

    It would nice if you guys post some SOR and FEA for us layman so we know what you are talking about.
     
  14. apex1

    apex1 Guest


  15. fredscat
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    fredscat Junior Member

    No daubt about that! In a few days I will post the ONE sketch of the simplified
    structure. My hand calcs could not properly solve some of the force directions. Maybe someone else can do much better than I. (I have been out of school for some 50 years!!
     
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