ABS Rules for Vessel intended for towing operations - Stability

Discussion in 'Stability' started by Niru, Jun 8, 2016.

  1. Niru
    Joined: Jul 2010
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    Location: Philippines

    Niru Mr.

    Good Day!

    I just wanted to ask your opinion on this matter.

    Looking at the attached "diagram" file - what is your understanding to the 40 degrees boundary for the residual dynamic stability?

    versus the

    5 Intact Stability Criteria
    v) the area of residual dynamic stability upto an angle of 40 degrees plus the angle of the first intercept etc....

    for example first intercept at 5 degrees.

    will it be = for the Area of RDS = 5 degrees upto 40 degrees


    will it be = for the Area of RDS = 5 degrees upto 45 degrees (+40 degrees)

    any thoughts?

    Thanks for reading.

    Attached Files:

  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect


    The diagram and text is very clear. The range, or extent, of the applicability is up to 40 degrees. Therefore whatever angle the heeling arm intersects with the GZ curve you add up to 40 degree as the maximum. The reason for the wording of "..up to..." is because in some cases the shape of the GZ curve and the heeling arm may be very different from that shown in the diagram. Therefore to ensure adequate stability the phrase ... up to .... is used. Meaning a maximum.

    So in your example if the intersect is at 5 degrees, the range is from 5 degree to 45 degrees absolute (45-5 = 40).

    But if you GZ curve meant that the range is let's say just 30 degrees...it does not mean you keep extending the range to 40 degrees. Since the curve means it is no longer possible, thus the range becomes less. Similarly if the shape of the curve meant you could - could - have more than 40 degrees, you cannot use this additional range. Because the phrase - up to - is used, i.e a maximum.

    Trust this helps?
  3. Heimfried
    Joined: Apr 2015
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    Heimfried Senior Member

    There is no difference between both wordings, because the area of RDS is defined as the area "to the right from the first intercept".
    So the heel angle from 0 to the first intercept contains no area of RDS.

    This is the way, I understand it.
  4. NavalSArtichoke
    Joined: Oct 2013
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    NavalSArtichoke Senior Member

    In many cases for smaller vessels like tugs, the angle of downflooding is the angle beyond which no area accumulation is permitted for any intact stability or other stability criteria.
    In other words, some downflooding point on a smaller vessel is going to become submerged before you reach 40 degrees or whatever cutoff range is mandated.
  5. Niru
    Joined: Jul 2010
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    Location: Philippines

    Niru Mr.


    Many Thanks Sirs'

    results on the analysis. tug vessels are sister ships but with different lightship and center of gravities (lcg & vcg)


    Attached Files:

  6. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I think that the rule does not speak of a range of 40 degrees but of a maximum value of heeling of 40 degrees. But this is just my interpretation.
    On the other hand, calculate the area under the curve of GZ to heeling angles greater than downflooding angle, it does not make sense
  7. Niru
    Joined: Jul 2010
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    Location: Philippines

    Niru Mr.

    Good PM.

    Point taken.

    i have to consider the downflooding angle...

    i guess ill just have to revised the results.

    thanks for noticing.

  8. Rabah
    Joined: Mar 2014
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    Rabah Senior Member

    Hi Niru,
    What has received after the record of downflooding points?
    NA Razmik Baharyan
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