calculating weights in a Inclining Test of a barge

Discussion in 'Stability' started by Amingenieria1980, Sep 4, 2019.

  1. Ad Hoc
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    Ad Hoc Naval Architect

    What utter immature childish egotistical nonsense....an excellent example of the profession you claim to be part of.

    Just a waste of bandwidth.
     
    Last edited: Sep 8, 2019
  2. rxcomposite
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    rxcomposite Senior Member

    Tansl- What is Rmt? Is it the metacentric radius (not radio)?
     
  3. TANSL
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    TANSL Senior Member

    I will answer, contrary to what I have said, courtesy of rxcomposite. Naturally, instead of "radio" I should have written "radious", my mistake (not very important, really). If one has notions of naval architecture and analyzes the formula, what else could it be?.
     
  4. Don92
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    Don92 Principal Naval Architect

    Hi Amingenieria1980!
    I have to agree with Ad Hoc on this matter, as for TANSL the phrase "Better to remain silent and be thought a fool, than to speak and remove all doubt" comes to mind.

    When conducting an inclining experiment, the purpose, or goal of the inclining experiment is to identify the vessel KG, though the experiment itself actually is used in order to calculate the vessel GM. The KM, being a property of the ship that can be identified via static calculation, can then be used in order to identify the vessel KG in combination with the GM value calculated during the inclining experiment in accordance with the following simple formula:

    KG=KM-GM

    Shifting a weight w through a known distance d in the transverse direction, say from the vessel centre line, will cause the subject vessel to heel to an angle which can be measured, θ. This will then form the relationship:

    tanθ = (w*d)/DISP*GM

    We should know the vessel displacement prior to conducting the test and the distance d depends on available deck space in which to shift the weights, in your case presumably beam limited as the vessel is a barge and therefore unlikely to have many obstructions on the deck.
    If we know the vessel displacement and the distance in which we have to shift the weights, we have two unknowns remaining, firstly the angle in which we would wish to incline the vessel and the weight(s) that we require in order to do so.
    Firstly, with respect to angle of inclination, IACS suggest that a minimum of 1 degree inclination be achieved and no greater than 4 degrees, generally speaking for large vessels you would expect the inclination to be around 1 degree (the weight required for suitable inclination above this becomes impractical for large vessels, ballasting is sometimes used), for medium vessels of approximately 100m you would expect around 1.5-2 degrees and for smaller vessels up till 4 degrees from the upright position.
    Once you define your target heel angle, all that is required in order to estimate the required weight is, as Ad Hoc correctly mentioned, some estimation of the vessel GM. If you have a static stability model of the vessel and a lightweight survey then this shouldn't be too difficult.

    Having completed the experiment, using the following expression we can determine the "true" vessel GM:

    DISP*GM=(w*d)/tanθ

    and then the KG using the aforementioned formula.

    I hope this helps!
     
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  5. NavalArchole
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    NavalArchole New Member

    Amingenieria1980,

    If you read through the most useful reply above (Don92s) you will have your answer. To add to this, if it is a flat sided barge, it is easy enough to obtain your approximate KM from a hand calc - then you can get your GM (KM-KG). KG is taken from the lightship weight estimate, or, since you are only approximating inclining weights, you can make a pessimistic assumption of 3/4 the barge depth.

    @TANSL, I have been a fan of boat design forum for many years, and have read many of your replies. I assume your reply to AdHoc wasn't sarcastic, as sarcasm to someone giving a reasonable answer doesn't make any sense, so why don't you (please, in less than 10 000 words) explain how we estimate the inclining weight without using a GM value?

    The floor is yours.......
     
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  6. TANSL
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    TANSL Senior Member

    @NavalArchole, the inclining test is carried out, precisely, to deduce the actual KG of the ship, which usually differs from that estimated to perform the previous calculations of the conceptual project. Therefore, starting from a KG value to calculate the KG value does not seem like a very correct method. You have to find another system.
    What we do know are the hydrostatic values of the boat, for different heels and for different trimmings. The ship's draft, forward, center and stern are measured to calculate the average draft and trim. Interpolating in hydrostatics, displacement, KC and BMt are calculated. With this, it is easy to calculate the weights to be transferred (using the formula in post # 3, duly explained). If you see that I am wrong, I will recognize my mistake without any problem.
     
  7. NavalArchole
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    NavalArchole New Member

    Tansl, what do you mean by the value KC?
     
  8. TANSL
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    TANSL Senior Member

  9. NavalArchole
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    NavalArchole New Member

    Tansl... your method is just simply wrong. Based on simple moments, you need an approximate starting vert centre of gravity to be able to approximate the required weight to achieve a desired angle of heel, For arguments sake, say your KG is at keel height, you will need much more weight to heel the vessel than if your KG is at deck height, would you not agree??

    Furthermore, you said that 'Therefore, starting from a KG value to calculate the KG value does not seem like a very correct method.', but we are not using a KG to calculate a KG? We are using it to approximate the weight required for an inclining experiment... I do not believe you have ever carried out, nor written up, an inclining experiment?
     
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  10. Don92
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    Don92 Principal Naval Architect

    Dear TANSL,

    The idea of starting from an estimated value in order to guide you in the right direction to finding the "true" value is common practice in engineering (Ask anyone conducting optimisation or indeed designing an experiment), start with a best guess and then improve. Given the aforementioned I find it highly surprising that you would think this an unusual endeavour and this only leads me to question both your qualification and character.
    You reference your equation sighted in post #3 which is as follows to my best understanding and in correct naval architectural parlance:
    w=(DISP*(BM+KB)*tanθ)/Dist (Δ should be used for displacement, but for ease of understanding I have used DISP)

    which implies that BM+KB=GM, though in actuality it equal KM

    The correct equation is as I mentioned in my previous comment:

    DISP*GM=(w*d)/tanθ
    w=(DISP*GM*tan θ)/d the same equation, though you assume GM to equal KB+BM

    Either I am correct or you are wrong!
     
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  11. Alik
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    Alik Senior Member

    I believe what TANSL means, that in case of the rectangular barge, VCG can be roughly estimated as half of depth D/2, and displacement is LxBxT.
    This will simplify the input to evaluate the inclining weights.
     
  12. TANSL
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    TANSL Senior Member

    First of all I want to say that I thank you for the kind and conciliatory tone with which you refute my arguments.
    @NavalArchole, the KG used by you cannot be said to be higher or lower than mine because I do not use any KG, I use KM.
    Although it may seem a lie, I have carried out several tens of inclining tests. As in my country these studies must be registered in the Official College of Naval Engineers, if anyone doubts my word, you can check in this body how many studies done and signed by me have been registered in it. In all those occasions I have used the formula that I have exposed and I have never had any problem, with monohull, multihull, small size or large ships.
    You estimate the KG to calculate the weights to be transferred, which allows you to obtain the true KG. That's what I mean when I say that they use the KG to get the KG and that doesn't seem right to me. It can lead to surprises if the angle of inclination obtained is too large or too small not to mention the cases, which sometimes occur, in which it is impossible to estimate the value of the KG because there is no data on the ship in question . That is why I use a method in which it is not necessary to know or estimate the KG. The method is approximate, like yours, but we know that in the case we are discussing it is not possible to use an exact method.
    When I clarified that we were talking about a large barge, I wanted to explain that the procedures of ISO 12217-1 were not applicable to it.
    Perhaps I have overreacted myself by qualifying your method of nonsense when what I should have said is that it seemed to me incorrect and that, therefore, with it I could not determine the position of the KG. I apologize for my youthful vehemence and you can call me uncompromising as many times as I have described that method as nonsense.:mad:
     
  13. TANSL
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    TANSL Senior Member

    Thanks to all those who, without starting from preconceived positions, without prior judgments, have honestly tried to understand what I wanted to say. Here lies a fact, which bothers me, if I am a naval architect, you can try to understand what I say. If I'm not, I can be called ignorant, you can say I don't know what I'm talking about, etc. That outdated corporatism is what I have always tried to combat. Thanks again.
     
  14. NavalArchole
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    NavalArchole New Member

    Tansl, I'm lost for words.... You are suggesting it is better practice to use the BM rather than GM to estimate required weight prior to an inclining experiment. I don't know any naval architect who would find this normal practice. I suppose your assumption that KB and KG are similar, then it's a 'quick and dirty' way of doing this, but in most cases probably totally wrong - so many other more reliable ways of approximating the GM... lightship estimate, empirical formulas, similar vessels, I could go on.

    You shouldn't be so quick to scrutinize other replies, when evidently, you actually don't seem to have a very good grasp of basic naval architecture and common practice.
     
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  15. TANSL
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    TANSL Senior Member

    I see that you are assuming something that I do not suppose. "You shouldn't be so quick to scrutinize other replies"
     
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