Inclining Experiment For Catamaran

Discussion in 'Stability' started by naserrishehri, Oct 7, 2015.

  1. naserrishehri
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    naserrishehri Senior Member

    Dear friends
    what kind of test weight normally use for inclining experiment of a catamaran boat like the attached picture?
     

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  2. TANSL
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    TANSL Senior Member

    Nice boat.
    For ships of this size, when shipyard media are scarce, I use 200 liter drums filled with seawater.
     
  3. naserrishehri
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    naserrishehri Senior Member

    Dear TANSL
    I used 200lit drum already for a similar boat but the width of new boat is 11.5m and i need 50 drums for 1degree inclination and there is not enough space for them.:(
     
  4. TANSL
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    TANSL Senior Member

    For a catamaran of 23 tons displacement at the time of the inclining test, LOA = 25m, breadth = 8.3 m, I used 880 kg, getting a tilt of 3 degrees.
    Of course the breadth of your boat is much higher but it seem to me strange that need so much weight.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    You can use solid pre-weighed certified weights and place them on the roof of the saloon, if space and lever is a problem. I've done this many times, see below:

    IMG_2961.JPG

    Or, you can use certified calibrated water ballast bags and place them into the voids. Then pump SW into them. This is more time consuming and not as 100% accurate. But for a catamaran, the accuracy of the the water ballast doesn't matter too much for the moment to calculate the GM, as the GM is high anyway. But it may affect your lightship displacement.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Clearly you have never inclined a catamaran before.
     
  7. TANSL
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    TANSL Senior Member

    Ad Hoc, you could have saved the comment, because you do not know what you are talking about, and I will not waste my time giving you more explanations, I do not deserve it.
    Attentively, a "fan" of yours.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Simple questions Tanls...have you personally inclined a catamaran before?
     
  9. gonzo
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    gonzo Senior Member

    I think catamarans have a very different stability curve than monohulls because of their huge initial stability. Maybe the regulations are not quite adequate for them.
     
  10. JSL
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    JSL Senior Member

    I inclined a cat some years ago. It was 65' x 28' x 9'(depth) for 225 passengers. At incline expt.
    disp. = 43 tons
    weights = 4 @ 1518 lb ea.
    move = 21.75'
    Pendulum = 169"
    Deflection= 1.57"
    GMt = 33.5'
    After 23 years the boat is still working and no stability issues.
     
    Last edited: Oct 7, 2015
  11. TANSL
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    TANSL Senior Member

    Simple answer, I do not remember how many, 10 or 12, and all designed by me, built under my coordination in several shipyards.
    Without knowing the displacement of naserrishehri's boat, my opinion may be wrong but it is not nonsense.
    Gonzo, rules are adequate for catamarans but have slight variations in relation to monohulls, mainly because, due to the large initial value of the GMT, the maximum value of GZ is obtained at heeling angles less than 25 degrees.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    Well, trouble is, that's basically the same thing. If it is wrong it can't be correct. If it is not correct..ask yourself, is it sensible, or is it misleading nonsense?

    So, without knowing anything about the vessel, other than - it is a catamaran, how can you arrive at this statement below - where it is based upon no facts?

    Thus, what is strange that you can arrive at an assumption of the vessel, the inclining weights seem high, without any facts. Not all vessels are the same and should not be assumed as such.

    So, please explain to me how you arrived at this answer....as I don't know.
     
  13. TANSL
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    TANSL Senior Member

    Ad Hoc, I will not miss even a minute of my time with you. I made a wrong comment and that's it, I have no objection to admit, my professional reputation is not diminished by a mistake however great it may seem to you, and many questions you ask. It is a shame to see that you have so much time for this nonsense. I am retired and these things amuse me, but you, do not you work ?. Sorry (well, not really sorry).
    Cheers, my friend.
     
  14. Alik
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    Alik Senior Member

    Inclination test for catamarans is not accurate at all. We did it many times, but...

    ISO12217-1:2013 Annex E:

    The vertical position of the centre of gravity (VCG) can be found using any of the following methods:
    a) an inclining experiment in water (see 3.5.6), the results being corrected to the appropriate displacement condition;

    b) an inclining experiment in air using a known length of suspension and moving weights transversely (as in water), the results being corrected to the appropriate displacement condition;

    c) calculation based on the calculated mass and centres of gravity of individual components, raised by an addition of 5 % of (F M + T C ).

    Method a) shall not be used for boats with a metacentric height greater than 5,0 m, since inclining experiments in water for such boats are liable to significant inaccuracies.

    Method c) shall not be used for boats with a metacentric height of less than 1,5 m, since significant inaccuracies may result. It may, however, be used for preliminary assessment.
     

  15. naserrishehri
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    naserrishehri Senior Member

    DEAR TANSL
    please see the GA. of the vessel in the attachment.It's light weight is around 185ton.
    total test weight should be at least 11ton.
     

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