Inclining experiment

Discussion in 'Stability' started by naserrishehri, Sep 29, 2021.

  1. naserrishehri
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    naserrishehri Senior Member

    Hi dear friends
    If you want to do inclining experument for a 40x11 m catamaran passenger ship, what material do you use as inclining weights?
    Its difficult to take big weights inside superstructure and pass from the doors and there are not enogh space on main deck for inclining weights.
     
  2. fallguy
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    fallguy Senior Member

    I apologize in advance as I do not know the answer, but can't a force be applied to the vessel and quickly removed? Like a lift boom or crane (assuming an area that can handle such pressures exists)? Or perhaps a pallet with water container? There must be some way it is practiced other than carrying weights around.

    BE0CA3F9-CEDA-4993-BC64-99D960128BE6.jpeg
     
  3. TANSL
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    TANSL Senior Member

    Heeling 3º a boat that can weigh more than 150 tons requires enormous weight. The normal thing is to do it with iron ingots or with 200-liter drums filled with water. In any case, a large number of weights are required, which must be located as far as possible from the centerline plane and distributed lengthwise so that the initial trim of the boat does not change. This gives rise to the problem posed by the OP: not enough space to place those weights.
    Having clarified that for those who are not familiar with the problem, it would be necessary to know the General Arrangement of the ship, and the means available to transfer the weights, to give an opinion that is not to speak for the sake of talking, without saying anything useful.
     
  4. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    When the OP presents a problem like this, it is a fair assumption that having gotten this far, they surely must know the normal way it would be done. In which case telling everyone the normal approach is more about typing, and less about helping, because they've already explained why they can't.
    In this case a much larger number of smaller weights may simply be unavoidable. Or failing that, a skilled carpenter may have to build a temporary structure distributing loads to hard points as pointed out by the NA or builder. Hard points that are small, or inaccessible, but can bear the necessary concentrated load.
     
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  5. TANSL
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    TANSL Senior Member

    @DogCavalry, do you think that my answer, the one that was addressed to the OP, has little to do with the original question?
    Don't insist on the "temporary structure" to distribute the weights among various hard points. That, given the existing difficulties in transferring the weights, would make it even more unfeasible. That is the reason why I ask about the means available to transfer the weights. It is not the same, as you surely understand, to carry a 500 kg ingot as a 200 kg drum. The second can be moved by a man, the first I think not. But, if that's okay with you, before we go any further in the brainstorming, let the OP provide us with more details. We are all eager to help, not to talk, right?
     
  6. bajansailor
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    bajansailor Marine Surveyor

    Many years ago in the late 80's I was working for a small design company in England.
    We had a job to do an inclining experiment on a ship (about 50 m long) on the Thames river in London - this vessel was being converted into a floating restaurant, and there was concern (re stability) about all the extra structure being added fairly high up.
    I remember my boss rented a van, and we picked up a number of empty 50 (or maybe 44 ) gallon drums to use - we did have access to a hose with water, and labour to help move the drums.
    And these drums worked pretty well.
    However this was on a monohull, with pretty fraught stability - I remember I was measuring the deflections on the plumb bob (the line was about 5 or 6 m. long) in the hold (the plumb bob was damped in a trough of oil) and it moved noticeably even when one person walked from one side to the other.
    So we did not need to have an awful lot of weight moved to do the job.
    The OP is inclining a 40 metre x 11 metre catamaran which will have much better stability than our poor top heavy restaurant ship, so the cat will need a lot more weight to heel her the desired amount.
    So, have some more drums available perhaps.
    Failing this, maybe use a crane on the shore with some known weights - for instance, many crane have additional weights that can be loaded on to them to help counter- balance the weight being lifted. And maybe some of these could be used, and moved about by the crane.
     
  7. TANSL
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    TANSL Senior Member

    @bajansailor I agree with you on almost everything. The problem here seems to be that there are not enough open spaces to place the weights, so they must be placed inside the superstructure, preventing the use of cranes to move them and making it very difficult to handle.
     
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  8. Ad Hoc
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    Ad Hoc Naval Architect

    It is very difficult if not impossible to Incline a catamaran that has almost no open deck nor space available inside.
    We have come across this many times with our range of 45m catamarans.

    Solution.
    Conduct a dry survey, with the surveyor, and provide a very detailed weight estimate to the Flag authority.
    You then add any discrepancies between the hydrostatics and weight sheet at 1.0m above the estimate VCG (from weight sheet) or sometimes 1.0m above the uppermost deck. Each Flag authority appears to have different means they prefer.
    That's it.
     
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  9. fallguy
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    fallguy Senior Member

    sometimes tansl, the person speaks to engage the question better or to get more detail

    I quickly disqualified. If the fact I opened my pie hole without a cv or knowledge bothers you, I apologize. I was really trying for the same as you to get an understanding of the layout which is why I offered a picture.

    Ad Hoc assumes there is no accessible deck at all and offered another alternative.

    I have seen a ship inclined by a hydraulic arm, but I cannot recall where. And, it is likely that is was designed with a hard point for the need.
     
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  10. fallguy
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    fallguy Senior Member

    Here it looks like either planned for tests or used lifeboat davits.

    But the test I saw used a ram on the pier.

    My apologies to tansl for being in water deeper than I swim...

    7B9BAB20-E012-4FC2-8AEE-6CFBBEC07A7B.jpeg
     
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  11. bajansailor
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    bajansailor Marine Surveyor

    Re Fallguy's photo above, I am guessing that the bags contain water? Or maybe sand?
    I wonder how many bags would be needed to heel a cruise ship of that size by a few degrees.
    (She looks a bit like a Silver Seas vessel?)
    Those lifting bags would also be useful for doing proof tests on the davits.
     
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  12. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Can one do the calculations in reverse? Lift the cat on one side, from an outboard edge. Determine stability from that by means of first principals.

    And @fallguy , TANSL's comment is directed at me, not you. I suggested carrying many barrels, and filling them with a hose, but he saw fit to comment as we saw. I deleted that suggestion and responded directly to him. I am not a proper NA, but I was an extremely good CE. Combat Engineer for those without military backgrounds.
     
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  13. TANSL
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    TANSL Senior Member

    @fallguy, you don't need to apologize to me for anything. We are here to entertain, to help if possible, and to exchange opinions. Often times, opinions are not necessary, but concrete and technically correct answers. You bring to the discussion what seems most appropriate and I comment on what your opinion seems to me, and vice versa. If my opinion makes it appear that you, or whoever, is not an expert on the matter, that is the game, as long as good manners are maintained.
    To tilt the boat by means of a hydraulic system from the pier is a serious mistake because the boat must float completely free of any tie so that it can tilt freely. I am not saying that you have not seen this procedure, I am just saying that it is nonsense and that the test carried out in this way is totally useless.

    @DogCavalry, using barrels filled with water, as I have said before, is a totally normal and correct practice. I have never said anything against it, on the contrary, it seems to me the most suitable for many small boats. But the advantage of barrels is that they can be moved by one man, no cranes are necessary (whether or not to use a hose is optional and does not affect the final result). If we place several barrels on a pallet, when there are no cranes available, it is useless and hinders their movement even more.

    For anyone reading this: the fact that you are not an NA does not have to prevent me from saying that you are wrong, if I believe that you are wrong.
     
  14. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Fairly said.

    So within our environment of mutual respect, have we helped
    @naserrishehri with his problem?
     

  15. TANSL
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    TANSL Senior Member

    I tell you, I repeat, @DogCavalry and @naserrishehrri, without knowing the boat you cannot say anything that is of real help.
     
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