Probabilistic damage stability

[manon]

Probabilistic damage stability (PDS), this term of stability calculation may be well known to the ship design, but i am very much new to this concept. Can anyone help me providing some information about the basic theory, calculation process or anything else?

thank you very much

[ontwerp]

Probabilistic damage stability has recently been "upgraded" to what is called the 2009 regulation. The regulations can be found in MSC 216(82), Part B: Stability.
There are some handy explanatory notes which are known as MSC Circ. 1226, which describes regulations in a bit simpler way.
I have attached those, along with a paper that gives an introduction and summary to probabilistic damage stability.

Basically it is too complex for me to explain fully, but I think the regs. and the paper should give you a good start.

In general the calculation is a form of statistics, where the probability of the survivability of the ship in different damage conditions is calculated based on the regulations and given an index. That attained index must be greater than the required index (given by the length and type of vessel) in order for the vessel to "pass" damage stability.

Good luck with it! The statistics and regulations can be hard to grasp, and I don't think you can do the calculation without software. I recommend NAPA (http://www.napa.fi/), most of the major Class. societies use it as well.

[Ad Hoc]

May be worth you reading this too:
http://www.mcga.gov.uk/c4mca/rp552_final_report_pdf_als-2.pdf

[manon]

Thank you very much, all of you. i have downloaded all the documents. Brother Ontwerp, i dont have NAPA, but i am using IPCA.
How could i get NAPA?

[ontwerp]

Maybe you could get NAPA as a trial or student version from them directly, you should contact their customer service. But it is a hard program to learn...just for an idea of the learning curve - I think as a beginner it would take you 2-6 months to build a model and do the calculation correctly.

PIAS can also do probabilistic damage stability and is a bit easier to learn, or maybe Delftship/Freeship has probabilistic damage stability - it is pretty easy to learn, but I don't know if the free version can do prob. damage stability.

If you are a student, maybe some other members know of some free software that can calculate prob. damage stability. If you work for a company I would suggest subcontracting the work since it is specialized and requires expertise, expensive software, and a knowledge of the "ever-changing" rules. :)

[ontwerp]

Manon, I just noticed you are in Dhaka. Just for your information, NAPA has offices in India.
And interestingly, I am currently working on stability calculations for a series of general cargo vessels for a shipyard in Bangladesh...

[manon]

really?? where are you now? are you in bangladesh? well, in that case, please receive my cordial invitation to our design firm. we will be very much happy and may be we have some discussion.
take care

[pavel915]

ontwerp,
Nice help,
Your attached docs are very helpful,

[ontwerp]

Pavel, glad the documents were helpful!

Manon, I am actually in Holland, but most of our clients are from other countries, so I myself am not in Bangladesh...but one of the projects I am working on is the stability calculations for a series of ships for the Ananda Group in Bangladesh. There is a good chance I will go there over the course of the project, maybe we can meet then, why don't you send me an email?

[zeroname]

May be worth you reading this too:
http://www.mcga.gov.uk/c4mca/rp552_final_report_pdf_als-2.pdf

many thanks

[ontwerp]

The comparison study of pre 2009 damage stability versus the 2009 regulations was interesting, I enjoyed reading it!

One thing they didn't compare was the change regarding trim. Damage stability calculated according to Reg.25 (pre 2009 rules) was calculated for 0 trim, and was applicable to all operational trims of the vessel.

With the new rules, if the vessel has an operational trim outside 1% of the subdivision length (example Ls=85m, then max trim=0.85 meters), then the calculation needs to be done for additional trims to cover the entire range of operational trims.
The resulting GM-Limit curves are to be combined to create an envelope curve which is the limiting curve for the ship.

Because a trimmed vessel (especially if it does not have a poop deck) can have worse damage stability when compared to an even keel vessel, I have noticed that damage stability required minimum GM with the new rules has become significantly higher for vessels that have an operational trim outside the 1% Ls range.

I was wondering if others have had the same experience, and if they are changing their designs because of it?