# Dynamic Stability -Seakeeping Cal. in Preliminary Design

Discussion in 'Stability' started by Murat124, Jan 8, 2015.

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### Murat124Junior Member

I would like to discuss the dynamic stability question

I have tested many work boats while their intact ( initial) stability is ok. They give abnormal results in seakeeping tests.
As I know there is a dynamic stability criteria question at IMO under discussion.

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### NavalSArtichokeSenior Member

I'm afraid you are going to be a little more clear on what is 'abnormal' about the results of these seakeeping tests.

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### Murat124Junior Member

80 degrees heeling = capsizing for oblique seas, blacksea wave statistics 2.5 m wave height (Tmean = 4 sn BlackSea wave statistic) 0 grond speed
This was the calculation on seakeeper.

Sea Trials

Ship's heeling amplitude average 12 degrees 2-3 sea state, 20 degrees max while initial stability were ok and heeling test result were reliable ( checked many times)

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### TANSLSenior Member

Hello again Murat124.
I agree with NavalSArtichoke, you should better explain your question. Meanwhile, I would like to make some considerations.
The initial stability is provided with an intact vessel. For me it makes no sense to speak of initial stability of a damaged vessel.
As I understand "seakeeping tests", I do not think that has anything to do with the initial stability and that this influences the test.
I guess for initial stability you are referring to the value of the initial GMt.

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### Murat124Junior Member

Please do not terrorise my posts, this is a serious request. you are not against a student or junior naval architect.

Main question was intact stability = initial stability = static stability criteria may not be sufficient for the evaluation of safety of vessels, it may be necessary to develope new dynamic stability criteria ( and this discussed on IMO)my aim was to test whether there was enough awareness about this question or not, but I see that not available unfortunately

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### NavalSArtichokeSenior Member

Sounds like some sort of near-resonant condition, or maybe parametric roll instability. It's hard to tell without more information.

A 2.5 meter wave height suggest a sea state of 5, which is moderate.

A sea state of 2-3 suggests wave heights < 0.60 m - 1.0 m, or very calm for open water. If your boat is heeling 12 degrees in such calm conditions, maybe intact stability is not OK after all.

What was the vessel heading with respect to the waves when the roll amplitudes were at a maximum?

What sort of GM does this vessel have?

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### TANSLSenior Member

Murat124, in no time I tried to "terrorize your post" (although I'm not sure what that means). I'm sorry you interpreted my words as an attack.
Going to what I think is your doubt, IMO criteria are taken into account various conditions of dynamic stability. Of the 5 or 6 stability criteria that apply to a boat, only one refers to the initial stability. The rest relates to the area values GZ curve at last, after all, is dynamic stability. Nothing is sufficient to ensure the safety of a boat but, in my opinion, the criteria of dynamic stability are many and very demanding because they are based on actual experience with boats, with their accidents, and are raised and discussed by naval architects with great knowledge and who meet frequently to talk about these issues.
I do not know if I misspoke but please, do not feel offended by my words.

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### Murat124Junior Member

Port Bow 135 degress heading ?

I will describe the situation with all details if you can give your e-mail adress to me

I will describe problem with all details if you can give me your e -mail adress

"What sort of GM does this vessel have?" could not be read ?*

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### kapnDSenior Member

going private

Murat
Why do you need to discuss this in private?
You have posted your question to a public forum, and have attracted some professional interest, as well as that of members like myself that are interested in learning here.
Unless you are taking this to a commercial level, paying for the information you wish to receive, please allow forum members access to the rest of the discussion.

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### Murat124Junior Member

if there was a standing discussion in private, I would not hesitate to share the results in public forum. Nowadays I am an unemployed Nav. Arch. It is more important to find a job in Europe or Turkey or somewhere else for me. Just because of this I have no time to spend for this question.

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