# Stability criteria for vessels fitted with deck crane.

Discussion in 'Stability' started by athvas, Mar 2, 2013.

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### gonzoSenior Member

My first language is Spanish, and it would be over the top in that language too; probable even more. According to TANSL's website he is an engineer and Naval Architect. I can't see how the concept of static and dynamic testing would get him in such a rage.

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### athvasSenior Member

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### TANSLSenior Member

I think it's time someone tries to help you. Although you must take this into consideration what Tad sais in post # 2.
I must say two important things from my point of view:
1 °. - For this purpose is totally irrelevant to the type of crane which carries the boat.
2nd. - There is no specific criteria for vessels with crane or cranes.
That said, what you need to do is the following:
1. - Choose stability criteria according to the type of your boat.
2.- evaluate various load conditions and verify compliance of criteria in each one.
3. - In the worst condition to make the study of lifting weights:

Me = P * (h *cos t + v * sin t)

Me = heeling moment
P = weight to be lifted, kilos
h = distance to center line of the point of suspension, m
v = height above the baseline of weight suspension point, in m
t = angle of heel

The value Me / Delta (being Delta the boat displacement load in this load conditio), will give a curve of variation of heeling arm for several angles of heel of the boat.

Calculate balance between weight heeling moment and righting moment of the ship, which is the point where the previous curve intersects the GZ curve of the loading condition under study.
The balance point, I think but I´m not sure, to be produced to an angle less than 10 °

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### gonzoSenior Member

That is not showing a counterweight.

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### d362622563Junior Member

Hello all. I am facing the same problem with athvas and found this post, I would like to discuss with more details if anyone is interested. I don't know if athvas has solved the problem?

On my side, I found some information as follows:
(1) API SPEC 2C 7th has proposed a vertical dynamic coefficient (Cv) of maximum 1.4 to include the dynamic factors during lifting, this coefficient is directly multiplied by the hook load to produce the vertical factored load which will be used to calculate the overturning moment.
(2) When calculating the GZ curve, the VCG need to be corrected by the effect of hook load which is described in ABS GUIDE FOR BUILDING AND CLASSING OFFSHORE SUPPORT VESSELS.
(3) The criteria can also be found in ABS GUIDE FOR BUILDING AND CLASSING OFFSHORE SUPPORT VESSELS, however I believe the critical criterion will be "The heeling angle based on the crane heeling moment and effect of the beam wind shall not exceed the maximum heel angle from the crane manufacturer. ".
The heel angle from the crane manufacturer is kind of small, if the manufacturer applies API code, it will be 2.5 deg. And that is what I am worrying about.

The Rules can be found in the following link:
http://www.eagle.org/eagleExternalP...itory/Rules&Guides/Current/180_OSV_2013/part5

Hope I have made it clear, and welcome to discuss more.

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### JSLSenior Member

If the crane has a heel limit of 2.5 degrees it has no place in a marine application. You will kill somebody!

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### d362622563Junior Member

Sorry, do you mean 2.5 deg is too big? I have no experience on board so please advise what will happen at 2.5 deg heel?

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### JSLSenior Member

It might be????Talk to the crane mfr and hire someone that knows what they are doing. I have seen 2 horrible accidents (3 deaths) regarding 'land' cranes used on the water. One started at a low heel and the barge listed to a greater angle, and then the boom snapped off.

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### d362622563Junior Member

The values are from both API code and a crane manufacturer, and this is the maximum heel angle through out the lifting operation. Ofcourse the heel angle will increase as the crane lifts to side way, we just need to make sure the heel angle never exceeds 2.5 deg when the crane works.

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### JSLSenior Member

2.5 degree limit is VERY tight..... You might get away with it. But, have patrol boats around to make sure your vessel does not roll from any wake and/or the weather is calm and there are no waves, and people on board do not move equipement, and all tanks are closed off so there is no transference of fluid, and, there is no wind induced heel, and.... I think you get the idea here.

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### d362622563Junior Member

Thanks for reminding, and those are what I am studying.

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