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

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

  1. TANSL
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    TANSL Senior Member

    That we all know and the first to know was the OP. No need to repeat it again. What, it seems, does need to be repeated is that the OP needs a solution for the hull that is now floating, not for the next hull to be built.
    Of course, the lead in the keel could be a solution, but before applying it, which can effectively reduce the performance of the hull, let the OP try other possible solutions, even if they are partial.
    In addition to lead, what other solution do you propose, Mr. Ad Hoc, for the existing boat ?. Let's be practical, for once.
     
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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Get rid of all ballast, and fit external flotation tubes, there is no other practical solution I can see.
     
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  3. TANSL
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    TANSL Senior Member

    I think you're right, I agree with you, Mr Efficiency, but the real challenge is to give a solution that does not diminish, or diminish very little, the performance of the hull. Maybe that total solution does not exist but it's worth trying things like, apparently, Nickname123 is trying to do.
     
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  4. Nickname123
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    Nickname123 Junior Member

    Hello,

    Yes, we are researching this issue, maybe we just reduce 200mm.
     
  5. Nickname123
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    Nickname123 Junior Member

    Hello,

    Thank you very much for your comments.

    I understand what you mean, but I am trying to reduce the inclining oscillation. And if making a new boat, it's very easy for me, I don't need to post this thread on this forum anyway ^_^.

    Yes, I have learned many things from this issue. I were believe designer too much more than what they can do.

    I hope I have chance to work with good designer in the next time.

    Thanks,
    Dương.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    You should approach a local shipwright for advice, especially, in my opinion, advice regarding the practicalities of adding a band of buoyancy along each side, whether it be inflatable tubes, or something else. That boat needs to be fattened up, considerably. Even the overall beam of it seems marginal to me.
     
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  7. Ad Hoc
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    Ad Hoc Naval Architect

    That is your only route. Cosmetic changes will do nothing to address them other than "look good".

    You need a hull form that provides the initial intact stability from the outset; which also provides better roll period, rather than adding bits that do not address the issue at hand - that being the statical stability.
     
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  8. Mr Efficiency
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    Mr Efficiency Senior Member

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  9. TANSL
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    TANSL Senior Member

    This hull has, among others, two problems :
    - initial stability is very low.
    - The righting arm is much smaller than normal up to approximately 50 degrees of heel. This is the famous GZ curve that Ad Hoc talks about, but that does not explain how to use it.
    This leads to two problems:
    - it is very easy to get the boat out of equilibrium.
    - the righting moment is not enough, rather than large heeling angles, to return the boat to the equilibrium position.
    The most effective solutions are undoubtedly increase the breadth in the flotation and decrease the height of the c. of gravity.
    What to do ?, that can only be decided by Nickname123 BUT, before that, there are certainly partial solutions, cheaper, which is important to try.
     
    Last edited: Jun 14, 2017
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  10. Mr Efficiency
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    Mr Efficiency Senior Member

    The obvious choice would be the "D" shaped collar.
     
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  11. TANSL
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    TANSL Senior Member

    Yes, from here, it seems a very interesting solution. I think that Nickname123 has obtained very valid answers in this thread but only he can value it properly, according to his circumstances, that we do not know.
     
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  12. Nickname123
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    Nickname123 Junior Member

    Hello every body,

    We have just done the repairing process for this hardtop speedboat.

    After considering all opinions, we have short meeting with boat owner and designer and we have been decided to repair the boat by add 2 x bilge keel along the hull.

    And the results is quite good, You can't think how glad we are to see the results. The boat is very stable, We have run tests with a lot of different modes even do the hard steer into the curve with maximum speed.

    I can't believe in my eyes when our boat get the good results like this. We just put 2 x bilge keels and not cut down the cabin.

    About the speed, when we manoeuvring with maximum load (12 persons - the boat weight is 3,28 tons), the boat can get 28 km/h. When we manoeuvring with 5 persons - the boat weight is 2,6 tons, the boat can get 35 km/h. It's quite good with 200 HP, 2 stroke engine, the engine can get 5000 rpm - not overload.

    Sorry I can not send you any pictures or videos about the water testing because I were in the boat so I can't take any pics when manoeuvring.

    Please see pictures for more details.

    [​IMG]

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    [​IMG]

    [​IMG]

    Thank you very much for your helps.
     

    Attached Files:

  13. Mr Efficiency
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    Mr Efficiency Senior Member

    What you have done there will greatly improve dynamic stability when planing, but not improve matters much, off-plane. I'd like to see a buoyancy band plonked on top of those "bilge keels" as you describe them.
     
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  14. Nickname123
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    Nickname123 Junior Member

    Hello,

    I am sorry but can you clarify about your comment? I don't really understand about your comment. What information do you need from me?

    Thanks.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    Those appendages will turn water down and generate lift, with sufficient forward speed, and give good stability underway, but when the boat is at rest or moving slowly, they will only act like bilge keels to dampen rolling, adding little in righting moment, and stability. I'd say your boat would not be leaning heavily in fast turns, as previously.
     
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