How to decrease the inclining oscillation and increase the stability on the boat

Discussion in 'Stability' started by Nickname123, May 30, 2017.

  1. Nickname123
    Joined: Aug 2014
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    Location: Viet Nam

    Nickname123 Junior Member

    Hello,

    Thank you very much for your reply.

    When we test the boat, I think our boat can't get good stability like this. But, I am very surprise about our boat. I don't know, but the boat is really good for now. The boat owner also test the boat and they can't give us any bad comment about stability.

    Thanks.
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Something like this........you are half way there !

    Buoyancy band.png
     
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  3. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Bilge keels can never increase the righting moment of a boat. It is not their mission. The only thing they want to do is to form some eddies that absorb part of the energy generated by the movement of balance of the ship due to a heeling moment.
    If, in addition, they improve the conditions of glide, therefore better than better.
    The stability only depends on the shape of the hull and the center of gravity of the boat as a whole. It can not be modified by the balance keels.
     
    Last edited: Aug 22, 2017
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  4. Mr Efficiency
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    Mr Efficiency Senior Member

    The boat would pick up a big increase in dynamic stability, TANSL. But that does not help when it drops off the plane. It will plane sooner, too.
     
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  5. TANSL
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    TANSL Senior Member

    It is very probable that you are right, Mr. Efficiency, I would not dare to affirm it without having made some calculation. But the main concern of the OP was more related to the initial stability and the magnitude and speed of transverse oscillations than to high-speed stability (which has nothing to do with what is normally understood as "dynamic stability").
     
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  6. Nickname123
    Joined: Aug 2014
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    Nickname123 Junior Member

    Hello,

    Thanks for your reply.

    When we plan to put the bilge keel, we also thinking about that. But, if we do like this, it will increase the boat weight and resistance.

    So, we have made it very strong already. It's almost a solid block.

    Thanks.
     
  7. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Looks like a very well executed job, and it does provide a basis to secure some nice buoyancy tubes to. You don't gain much extra righting moment from it as it is.
     
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  8. JSL
    Joined: Nov 2012
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    JSL Senior Member

    Mr Efficiency - you got it right for a quick fix..
    It is quite obvious why this boat has problems....even a rudimentary 'design check' would have raised stability questions.
    I have been involved with several 'sponsoning' (not bilge keels) jobs on boats from 30' to 70', planing and displacement hulls. One alternative is to make the sponson side a bit higher which essentially reduces the amount of flare: adds to the hull side volume to give more righting force. The down side is the sponson 'flat' will 'slap' when running and in waves.
    As to construction, just like the existing hull.. be it FRP, steel, wood, or aluminum
     
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