Looking for help determine speed and power requirements of potential power catamaran

Discussion in 'Hydrodynamics and Aerodynamics' started by massandspace, Nov 8, 2017.

  1. massandspace
    Joined: Sep 2017
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    Location: Salt Chuck

    massandspace Junior Member

    I am looking for help (help more than "advice") on determining the feasibility of converting 27' catamaran sailing hulls into a medium-speed, displacement power catamaran.

    I have drawn the underwater hull surfaces as best I could with careful hand measuring at 24" stations in Rhino 3D.

    Is there anyone who can help me in determining the following based on the hull CAD file:

    1. Horsepower required to run the boat at different speeds.
    2. Maximum hull speed in flat water using a reasonable amount of fuel.

    I am willing to actually pay someone who can determine these things relatively accurately....to see if the idea will work....and possibly to determine to what extent the rear ends of the hulls would have to be modified to make it work....if that is even possible. I have also thought about adding some type of foil structure to the sterns to prevent what I anticipate will be the main problem of stern squatting.

    Thanks for reading and possibly pointing me in the right direction.
     
  2. TANSL
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    TANSL Senior Member

    Do you have a body lines plan?. Couold you show us what information do you have to create the 3D model of the ship?. What speed is, more or less, "medium-speed" for you?
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

  4. massandspace
    Joined: Sep 2017
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    massandspace Junior Member

    Hello

    I have a 3D CAD file of the underwater section of the boat....I can take a side view photo of that, but I think whoever can help would need the 3D model....no?

    I am looking to get about 10 knots of speed out of two 15/20 hp motors.

    Also, does anyone know if it is possible to contact a member directly?
     
  5. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I do not have a specific software for catamarans. I can study your boat with Maxsurf (Hullspeed) which will give an approximate idea of the power-speed curve. Could we have the 3D model of your ship in .igs, .dxf or .3dm format?
     
  6. massandspace
    Joined: Sep 2017
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    massandspace Junior Member

    Hello

    OK...how can I get the file to you? Is there a way to communicate directly?
     
  7. massandspace
    Joined: Sep 2017
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    Location: Salt Chuck

    massandspace Junior Member

    I just noticed the upload file button....I will try to upload the file in .3dm format when I can get my main computer online (on iPad now).

    I appreciate any help, but please understand that there are 2 hulls in the catamaran....any software used for monohulls I do not think will work, as there is wave interaction between the hulls.....????

    Anyway, I will attempt to download CAD file soon
     
  8. TANSL
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    TANSL Senior Member

    Yes, that is why I have specified that it is Maxsurf and that it will only be an approximate result. I only have this software and a spreadsheet for the Holtrop-Mennen method. If this serves you, great. Otherwise, we will have to wait for another member of the forum, with the appropriate software, to offer the correct calculation.
     
  9. massandspace
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    massandspace Junior Member

    OK great....I will post it...I hope by tomorrow. Thansk for your offer to help.
     
  10. massandspace
    Joined: Sep 2017
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    massandspace Junior Member

    I have attempted to upload the Rhino 3D (.3dm) file of the underwater sections of the catamaran. The front of the boat, by the way, is the part touching the "x" axis.....at the bottom if the files opens the way it opens for me.

    The hulls are spaced properly as well. Not sure how much one will affect the other in real life.

    Thanks to anyone trying to help.

    David
     

    Attached Files:

  11. TANSL
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    TANSL Senior Member

    I enclose the curves that I have obtained by 4 methods. The dispersion is very large but it is possible to give an idea of the maximum and minimum values between which reality can be found. I know it's not very clarifying but use it as best you can.
    Given the relatively large separation between the hulls and the small breadth of them, it is likely that at speeds less than 10 knots the interaction between hulls is very small.
     

    Attached Files:

  12. Ad Hoc
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    Ad Hoc Naval Architect

    Actually it is much easier than you think, and being suggested above too.

    All you need is:

    1) The displacement you wish to run at
    2) The WSA at said displacement.

    That's it.
     
  13. sigurd
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    sigurd Pompuous Pangolin

    The displacement is 1909 liter and the WSA 12.6 m2.
     
  14. sigurd
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    sigurd Pompuous Pangolin

    massa, the shape is too wavy, your boat is probably much smoother. Tansl, is that the hull you put into your calculations? Easiest way I make hulls is with T-splines in Rhino. It is an incredible amount of work to manually loft too many control points. The only sane way to use many control points is to start with a fair shape (a sphere) and use scaling selectively. Otherwise make guide curves from fewer control points and lay your 3d control points on the guide lines. There should be a curve fitting tool for control points, but I haven't found it. Meanwhile, easier to use as few points as possible.
     

  15. TANSL
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    TANSL Senior Member

    @sigurd, I have used exactly the shapes presented by the OP, with some slight modification. In my opinion shapes are not too well obtained, the boat will look like these shapes but it is not the same, for sure. But it is the only thing we have. Getting the exact shape s of an existing boat is not easy work.
    See hydrostatic properties that I have obtained for a draft of 0.398 m.

    Snap34.jpg
     
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