Hydrostatics and Intact Stability of tug 25m

Discussion in 'Stability' started by Rabah, Aug 19, 2015.

  1. Rabah
    Joined: Mar 2014
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    Location: Bulgaria

    Rabah Senior Member

    Hi All,
    I want to acquaint you about one updating a tug 25m.
    The original tug is in operation in one of ports of the Asian states.
    The version offered to your attention differs from the original bottom and sides. Out-to-outs of the tug are reserved, as well the deck line and the line of keel in CL.
    Original bilge it is carried out by radius of rounding-off. Updating offered me has two chines for a bilge part.
    This new version has major advantages - the hull to make from the technological point of view easier that is the production expense will be decrease.
    The model is created by me on program Delftship Professional. The hydrostatics are carried out on Orca3D, by means of export-import IGES file from Delftship Professional in Rhinoceros.
    The attached files illustrate the model and calculations on hydrostatics.
    The main sizes and characteristics of the tug:
    L=25m; B=8,9m; T=2,9m; D=284,8t; LCB=LCG=13,56m; VCG=2,8m
    Coefficients / by Delftship Professional/:
    Cb=0,486; Cp=0,638; Cwp=0,8407; Cx=0,7618
    Continuation follows.
    ______________________________
    NA Razmik Baharyan
     

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  2. DCockey
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    DCockey Senior Member

    Why is this design easier to build? Is the plating developable?
     
  3. Rabah
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    Rabah Senior Member

    Hi David,
    From the enclosed file it is visible that only areas marked by red color do not satisfy the conditions for developability.
    __________________________
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  4. NavalSArtichoke
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    NavalSArtichoke Senior Member

    Don't you think those areas could be fixed?
     
  5. DCockey
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    DCockey Senior Member

    What software and criteria did you use to determine developability?

    Several years ago I visited a designer and builder of tugs in the US. Their designs had straight frames and non-developable surfaces. It is easier from them to shape plating then to bend frames.
     
  6. NavalSArtichoke
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    NavalSArtichoke Senior Member

    Most single and double chine workboats built along the GoM are built in this fashion, i.e., with straight framing. OSVs used to be built this way, too, but the larger boats over 200 feet have adopted North Sea style hulls with some curved plating at the pointy end, mostly single, rather than compound curvature, though.
     
  7. TANSL
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    TANSL Senior Member

    I have worked with 5 or 6 different projects of modern tugs. You can not say that I'm an expert, but in my opinion, the stern is totally inadequate for a tugboat. The keel neither seems right to me.
     
  8. Rabah
    Joined: Mar 2014
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    Rabah Senior Member

    Hi every one,
    I shall try to answer all arisen problems.
    1. Fixation of zones in red color has no important value in initial design stages. It is made later on the following stage in nesting documentations.
    2. The criterion for developability is only one - whether have the surface/or separately taken shell plate/ a bicurvature or not. The program itself determines it. Particularly for Delftship Pro it is a function calls „ developability shading mode”.
    3. Single or double chine of bilge it is usually applied at high-speed ships- gliders and ships with legs.
    For river displacement ships it is applied irrespective of the length- for example sectional structures for pushing.
    For displacement see going ships is applied usually for auxiliary fleets for example like this tug.
    4. If not we shall speak about double bilge chine in remaining as the stern and keel / buttock-line CL/ are precise copy from the original project of the tug, which now it is successfully maintained.
    ______________________________________
    NA Razmik Baharyan
     
  9. Rabah
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    Rabah Senior Member

    Hi All,
    Let's go on further with calculation of Intact Stability.
    From the attach files you can see the coordinate system and critical points:
    - Deck immersion points in middle CP1 (P/S)
    X, Y and Z =12.5m, + - 4.432m and 4.406m
    - Downflooding Points CP2 (P/S)
    X, Y and Z =12.65m, + - 2m and 5.2m
    In the Silhouette you can see the following data / by draft T=2.9m from BL/:
    Wind area Aw=106.04 m^2
    Zw=5.884m from BL
    Xw=13.665m from AP
    Lateral area 60.358 m^2
    Lateral center of effort:
    X=13.627m from AP
    Z=1.318m from BL
    For Full displacement we have:
    D=284.79t; LCG=LCB=13.561m from AP; TCG=0; VCG=2.8m from BL
    We calculate the Intact Stability with program Delftship Professional using criteria of International Code of Stability IMO A.749.
    You can see the outcomes in the Stability Diagram and Table to it.
    In the total have received:
    Ratio of Area A / Area B = 0.136
    Or coefficient of weather criterion Kw=Area B / Area A = 7.35> 1
    by Wind pressure 51.4 kg/m^2=504 Pa for operation in an unlimited navigation area.
    Continuation follows.
    ______________________________
    NA Razmik Baharyan
     

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  10. TANSL
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    TANSL Senior Member

    Dear friend Rabah, with all due respect, if all the technicians who visit this forum published each routine calculations he does, this would be a terribly boring forum.
    If someone does something novel itself would be welcome to publish it. Otherwise, better prevent us from suffering. This life is to enjoy.
    Cheers.

    (I repeat once more : the stern of your tug is not correct)
     
  11. Rabah
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    Rabah Senior Member

    Hi Tansl,
    I am correct on title of my publication. In fact you do not think that I shall make only half of work. I always finish that have planned. And if it is not interesting to you and it is not curious - that an output is one, simply do not read. Then you will suffer less.
    __________________________
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  12. TANSL
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    TANSL Senior Member

    Hi Rabah, you are quite right, you can publish what you want and, if bores me, no one forces me to read it, but frankly know that someone does the same thing I've done dozens of times, it has no incentive, nor I think that has sufficient merit to be published.
    Again, adjust the stern of your boat as it is not right for a tugboat.
     
  13. Rabah
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    Rabah Senior Member

    Dear Tansl,
    You are simply quarrelsome. See attached files.
    ____________________________
    NA Razmik Baharyan
     

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  14. TANSL
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    TANSL Senior Member

    Dear Rabah, thanks for your patients words. Perhaps I am quarrelsome, I do not know, what I do know is that those are different sterns.
    The ship on which you have based has normal stern in such type of tugs. The model that you have done has a stern that is not correct for this type of tugs.
    And the keel that you've invented is "curious", useful ?, I don't think so.
     

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  15. Rabah
    Joined: Mar 2014
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    Location: Bulgaria

    Rabah Senior Member

    Hi Tansl,
    Why do you misrepresent the things?
    I do not say that I want full identity of the stern. I have made only identity of the contour of CL on whole perimeter.
    The stern is very good even perfect!
    Concerning the keel - really the aft edge is sharper. But it can be corrected on the following stage if it is necessary. But now there is no sense.
    Thanks for the comment, but all the same it is only your personal opinion. Only words unstiffened by arguments.
    _________________________
    NA Razmik Baharyan
     

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