Power-Cat. concept design

Discussion in 'Boat Design' started by Lee01, Jun 27, 2017.

  1. TANSL
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    TANSL Senior Member

    But Rhino 3D platform nor any other software can do any reliable resistance calculation if you have not previously done a study of weights and c. of g. I think, but it is only an opinion, that you would let yourself be advised by a technician because I see some gaps in your approaches.
    Good luck with your project.
    Oh yes, another doubt : Snap6.jpg
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    The frontal view appears to show more hull on the inside than the outside, opposite of what the OP suggested.
     
  3. Alik
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    Alik Senior Member

    1. Rhino/Orca does not calculate resistance of catamarans, or I am missing something?
    2. Displacement is usually calculated by table of weights. This includes structural weight, which can only be obtained from preliminary calculation of structure and lamination schedule, or from similar craft. Rhino etc. is of no use here.
     
  4. Lee01
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    Lee01 Junior Member

    @TANSL don't take measures on a rendering in perspective as they are not accurate, the inner of the hulls has less area. Cg and Cb are at the same location, the mountain moves to the prophet or otherwise. Orca has a performance prediction and new CFD plugin. For weight, only similar vessel was studied and also some useful literature online..
     
  5. TANSL
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    TANSL Senior Member

    The picture must have little resolution so you can not see that I have not taken measurements. I have only drawn a few lines and I have written several texts trying to show that the distance between hulls is probably not the third part of the breadth (BC/3), as you said.
    If you allow the boat to float freely, the coG and the c of buoyancy will automatically be placed in the same longitudinal position. The prophet does not need to move. But that does not mean that the equilibrium position is correct. And that is one of the things that, for a long time, you should have checked.
    I'm sure Orca or its new plugins, which I do not know, are unable to do any study if you do not calculate the weight and coG of the boat.
    Similar boats? It may be but if there is a boat so similar to this that you can get reliable data, it means your boat would not be so new. I do not think, although I can be wrong, that there are similar boats with a structure that can withstand 49 knots.
    But, in any case, the designer is you and, therefore, you know better than anyone, I suppose, the problems that your boat can have and how to solve them. My advice is that you do not rely on similar ships, if any, and that you make your own calculations.
    Online documentation?. How much documentation on line should you study to be able to design a boat of the performances of yours ?. The answer, imo : much more documentation than anybody could read and assimilate in a long time.
    You have made a beautiful render. Find someone who can turn it into a boat design.
     
    Last edited: Jul 2, 2017
  6. Alik
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    Alik Senior Member

    Performance prediction in Orca is Savitsky and Holtrop. None of them is suitable for catamaran! For the CFD, I doubt You did it; but if yes how do You validate the results? CFD without validation is useless for catamaran.

    Where did You get weight details of similar vessel, say for structure? Especially considering Your very high design speed, structure should be designed for higher g's, there is no statistics for such fast catamaran craft, unless You have designed few of them Yourself before :)
     
  7. Lee01
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    Lee01 Junior Member

    If after preliminary scantilings and weight calculation the Cog is so far as 50 cm forward than it should be, the boat would change the static trim but I can move the pilothouse after and also move the hypotetical tanks and the generators. And if for some reason I have to change the underwater volumes, it is not a big problem.
    The Savitsky used in Orca 1 can calculate the resistance of a (symmetric) mono-hull, I then doubled the results for the cat. 49 knots didn't seem a relative high speed for a hard chine MH to generate a lot of RAM effect but this and aerodynamic coefficient were estimated to add 10% more of total resistance. I haven't used any CFD ever. Alik, one of the most specific document that I have found about power catamarans is online google for Nazarov Power Catamarans Design, very good reading ;)
     
  8. TANSL
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    TANSL Senior Member

    Something else you'll have to add, do not you think?
    Of course not but with hard chine or without it you will have to calculate the scantlings to withstand the accelerations produced by that speed as well as the impacts of the waves on the inner shells and on the wet deck.

    By the way, nice trick to tell Nazarov that you have read his study. Although this will not prevent you from having to perform many more calculations than the ones made so far.
    Allow me a question that has nothing to do with hydrostatics, weights, etc. but that is important: Do you think that in the pilothouse there is enough space for 12 people to comfortably cohabit in it ?.
     
    Last edited: Jul 2, 2017
  9. Lee01
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    Lee01 Junior Member

    Hehe, do I have make the calculation? Inside the pilothouse is 4,5 x 5,5, mq of wich 5 mq is taken by six seats a four seats sofa, the ramaining 20 sqm can accomodate more than 10 people a little squeezed with the reccomended from ISO space of 450x750 mm for each one but it has comfort only for a dozen of seats.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Can you get a top speed of 49 knots in a (46 ton here) boat using around 60hp/ton ? I don't know many, or any boats that can do that. More like 100hp per ton in any I've been in.
     
  11. Lee01
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    Lee01 Junior Member

    Thanks again Mr.Nazarov!
    Tansl don't scratch the gelcoat with your marks please. I would accept a lower speed prediction and choose a bigger engine like the MAN V-12.
     
  12. TANSL
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    TANSL Senior Member

    I do not want to scratch anything with my marks. I'm trying to make you understand that you would do well to commission someone who knows the subject, who turns what is a nice render into a viable boat project.
    You do not have to accept a reduction in speed. If you want your boat to reach 49 knots, you must design a boat capable of reaching them and, if you do not know how to do it, ask some expert to do it. The other possibility is to try to find out the maximum speed that the render you have thought can achieve. It is about putting some engines as large as possible, as long as they fit in the hulls.
    Do not hate me, please, for trying to show you that designing a ship consists of more than drawing a nice object with a rendering software.
    And we are talking only about the ship as a floating object. Do you really believe that as a hotel that object is capable of achieving the goals you pursue?.
     
    Last edited: Jul 2, 2017
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  13. Alik
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    Alik Senior Member

    Speed prediction is very optimistic. To say more - unrealistic.
     
  14. Lee01
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    Lee01 Junior Member

    Okay speed is overestimated, I am open to any collaboration should someone qualified be interested in a similar boat
     

  15. TANSL
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    TANSL Senior Member

    Define, firstly, the SOR of the boat and your conditions so that the experts can evaluate if it is worth the collaboration. Good luck.
     
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