IS Code Stability Criterion / Autohydro

Discussion in 'Stability' started by Jordan KL, Apr 11, 2022.

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Jordan KLJunior Member

I am evaluating the Intact stability of a passenger vessel and a pontoon according to IS Code 2008 respectively, by using Autohydro.

I set the following criterion from Part A, 2.2 of IS code in Autohydro for the passenger vessel;

LIMIT(1) AREA FROM 0 TO 30 OR FLD > 0.055
LIMIT(2) AREA FROM 0 TO 40 OR FLD > 0.090
LIMIT(3) AREA FROM 30 TO 40 OR FLD > 0.030
LIMIT(4) RA AT 30 or Max > 0.200
LIMIT(5) ANGLE FROM 0 TO MAX > 25
LIMIT(6) GM at Equil > 0.150

And I set the following criterion from Part B, 2.2 of IS code in Autohydro for the Sea-going Pontoon;

LIMIT(1) AREA FROM 0 TO MAX OR FLD > 0.08
LIMIT(2) ANGLE FROM EQUIL TO RA0 OR FLD > 20

What concerns me is that whether I should consider "Down Flooding Points" in the criterion of Sea-going Pontoon, even it was not mentioned in IS code. It seems it is reasonable to take it into consideration even it is not mentioned. If the answer to the question is "YES", Does it mean I need to apply the same concept to Area under curve from 0 - 30 degrees in passenger vessel case?

It is so strange to me that IS code requires to consider down flooding points from 0 - 40 and 30 - 40, except 0 - 30. Please share your view.

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jehardimanSenior Member

Hello, welcome to the forum.
You need to read, and understand, your spec's. For a "Sea-going Pontoon" note requirement 2.2.1.6....there is no down flooding angle. If your design has an opening allowing it to flood, it is not a "Sea-going Pontoon".

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Jordan KLJunior Member

Do you mean all of the ventilations on a sea going pontoon should be fitted with "self closing vent head"?

In the meantime, how to explain the 0-30 range without downflooding requirement in the general criterion? It really confuses me.

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jehardimanSenior Member

Why would there be any vents in a "Sea-going Pontoon"? A pontoon is only to support a load, such as a bridge, pier, causeway, brow, or as a berthing structure. So no active tanks, no active vents.
As for the other, read Part A 2.2.1 again. There is no requirement to have a down flooding angle greater than 30 degrees, only that the area under the righting curve be 0.09 metre-radians at the down flooding angle.

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TANSLSenior Member

If the pontoon has tanks for the transport of liquids, the answer to your first question is yes.
Regarding the second, the curves of the GZ (righting arm) or DN (work consumed to tilt the ship) values have nothing to do with the openings that may exist in the ship's hull. They are continuous curves, in general, between zero degrees and 360 degrees. What happens is that, if a list is reached at which flooding occurs, these curves are no longer useful (the volume that provides buoyancy decreases), they cannot be used beyond the angle of flooding.

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Jordan KLJunior Member

Thanks,TANSL.

I share the same view with you that downfloodng points should be considered even in Sea-going pontoon case, if there is any cargo tanks below deck. If this the case, why IS code does not mention downflooding point in Pontoon’s criterion?

I have no doubt on the influence of downflooding point in GZ curve, anything under the curve after downflooding point should not be considered. However, Part A, 2.2.1 clearly mention the area under curve from 0-30 should not be less than 0.055, but it requires 0-40 or downflooding angle should not be less than 0.09, why is this difference? why is the concept of downflooding angle introduced only in the range of 0-40, and 30-40? why it is not included in 0-30? Furthermore, why it is not considered in the criteria of max righting level? how about if the downflooding happens before the max righting level? do we still accept the max righting level in this case? The ship begins to flood after the point, is it still meaningful even the max. righting level is higher beyond this point?

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TANSLSenior Member

The curves beyond the point of flooding are useless, they are interrupted at that point, there is no more curve beyond, the curve does not exist. Therefore, if the area under the valid curve does not have the required value, or if it does not reach 30 degrees, the stability criterion is not met.

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Jordan KLJunior Member

Again, we share the same view on this point. But why IS code was written in such a strange way? we both agree that the downflooding points are so critical in GZ curve, why it is not mentioned in each criteria of the code? As far as I know, the general criterion has been there back to last century, if there was such a big flaw, why it has not been corrected decades ago? And I have noticed people use Autohydro commands like the one in my first post in different occasions, which are incorrect if the above our view about downflooding points is agreed.

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TANSLSenior Member

In my opinion there is no need to warn of anything, it is not a flaw (big or small) in the regulations, it is that the curve does not exist beyond that point. It would be a new curve, different, not the curve that the rules speak of. The problem may lie in the fact that no software is a treatise on naval architecture.

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jehardimanSenior Member

I don't see how you two can arrive at this conclusion given the text of the Code. Quoting from Statutory Documents - IMO Publications and Documents - International Codes - 2008 IS Code – International Code on Intact Stability, 2008 - Introduction - 2 Definitions
Unlike the US CFR requirements for Tank Barges ( https://www.govinfo.gov/content/pkg.../pdf/CFR-2008-title46-vol1-chapI-subchapD.pdf ), I don't see how you could arrive at a "Tank Pontoon" under 2008 IS Code given the requirements of Introduction/2.16.3, i.e. a "pontoon" has no cargo tanks. <shrug>
2 Definitions https://imorules.com/GUID-2901C4B2-57B2-4945-9711-F587A8D156E2.html

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TANSLSenior Member

You are absolutely right, but if the OP's pontoon transports liquids in its "holds", not on deck, the tanks must have vents that must comply with the standards established for them. In that case, can't that device be called a "pontoon"? Well, very well, call it whatever you want. And now we are going to see what stability criteria can be applied to that "artifact".
I don't think I mentioned in my answers what code that artifact had to comply with, but maybe I'm wrong.

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RAraujoSenior Member - Naval Architect

In principle all compartments, independently of carrying cargo or fluids and which are not fitted with other ventilation arrangements, shall be provided with air pipes (vents). See below an example for BV Rules for Steel Ships

Regarding your doubt on considering the flooding angle if less than 30deg maybe the following can help:

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Jordan KLJunior Member

Thank you very much. This is absolutely what I want to clarify in concept in order to make sure my job can be done correctly.

In the meantime, this is also my knowledge that even a void compartment on board should be vented, because of the need to balance atmospheric pressure, otherwise the compartment will be inflated or shrinked to deform in extreme case.

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