Experimental Catamaran Hull Rocker

Discussion in 'Multihulls' started by useragentseven, Jan 27, 2020.

  1. useragentseven
    Joined: Apr 2017
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    Location: Florida

    useragentseven Junior Member

    Drawing up a 48 foot (14.6304 m) catamaran hull, and EXPERIMENTING w/Rocker shape.

    Rocker_View_1 | Boat Design Net https://www.boatdesign.net/gallery/rocker_view_1.27280/
    Rocker_View_2 | Boat Design Net https://www.boatdesign.net/gallery/rocker_view_2.27281/

    The entire keel/centerline is curved (there are no straight lines). However, I have drawn the rocker substantially lower towards to bow, much lower than the stern (since, the bow is a finer/narrower width).

    Since, I have noticed many catamarans with deep rockers pitching forward and aft, as they go through and over waves, I have drawn the rocker lower, forward towards the bow to possibly acheive more flotation forward (and to attempt to keep the bows from diving as much).

    I understand that a deeper rocker is beneficial to help the boat tack/turn better, but, could I not just increase the area of the daggarboards and rudder to acheive this instead?

    [The inboard side of the hull, of course, is not complete yet but, will feature a chamfer panel (to also provide floatation forward, if diving occurs).]

    Any thoughts on rocker shape?

    Thank you!
     
    Last edited: Jan 27, 2020
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Frankly, I don't see anything remarkable or new in those pictures. Could you give more details or show the full hull? Thank you.
     
  3. useragentseven
    Joined: Apr 2017
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    useragentseven Junior Member

    Sorry. I guess I mislabeled this post. I wasn't really going for remarkable, just less diving/pitching.

    Thanks!
     
  4. Gary Baigent
    Joined: Jul 2005
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    Gary Baigent Senior Member

    Put lifting foils on your boards and rudders, pitching problems solved?
     
    Last edited: Jan 30, 2020
  5. redreuben
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    redreuben redreuben

  6. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    You can't really draw a hull on the computer and expect it to float as you have drawn. It won't.
    You first need to do a weight study of the entire structure and work out the CG. Then you get the CB to be directly under it.
    This means you have to design the structure as you design the hulls in a spiral, back and forth.
    My guess is that these hulls will lie back and float stern down and not as drawn. You can change volume distribution how you like on paper but the boat will rotate to put the GB under the CG. You can't get round it.
    Many designers have gotten this wrong and have had to have transom extensions installed - do the weight study or at least get some from similar style boats.
     
    useragentseven and Manfred.pech like this.
  7. useragentseven
    Joined: Apr 2017
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    useragentseven Junior Member

    Thank you! Very informative! The kind of information I was looking for.
     
  8. useragentseven
    Joined: Apr 2017
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    Location: Florida

    useragentseven Junior Member


  9. useragentseven
    Joined: Apr 2017
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    useragentseven Junior Member

    Wow. Big task there!
    Would many designers be willing to part with their weight studies? Especially considering their hours, and experience into such a calculation?
     
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