Heavy Lifting Stability Criteria

[Guest-3-12-09-9-21]

http://blog.al.com/live/2008/05/fire...laze_on_b.html

What are your thoughts on the A-frame that is on this vessel? It make me somewhat nervous - although I am going more on speculation, rather than fact.
--Chuck

[Guillermo]

I understand your concerns, but....what about this one?
http://www.oilpubs.com/oso/article.asp?v1=7158

Cheers.

[navarch25]

the area below the rightning curve represents the heeling energy absorbed.

these criterias are developed based on extensive resarch spending millions of dollers..

[safewalrus]

Jib that crane out on either beam with any kind of load on and your going over, simple! over the stern is not much of a problem, but like all things when the chips are down and the crane driver is concentrating on the job if he swings a little to far over..........................no matter how good the mate on the bridge is at transferring ballast, your swimming

[murdomack]

Aye Walrus, something does not look right here. Either the ship is drawn too small or the crane is drawn too big.
It may be that the 1800 tonne crane will only operate through 180deg, arcing from ahead to astern and being on the starboard side could only swing to port. It's hard to tell but she would need to be slab sided to get sufficient bouyancy to even allow this. She does look quite beamy but nothing like the old lifting barges that were converted from tanker hulls when we were nippers.
On the Normand Installer, they can lift or lay 1000 tonne on the seabed, but it means opening a moon-pool just aft of the main winches and erecting a tower to hang off. They do 350 tonnes on the A-frame over the stern. I think she is over 5000 tonnes so I don't know what this one will need to be

[Guillermo]

You've got this one, too....

[Guillermo]

And also...

Cheers.

[Guillermo]

Or even this 90 m height, 3000 tonnes crane one, under construction in Singapore...

[Guillermo]

But nothing compared with this 180 m length vessel with its 5000 tonnes, 150 m over deck crane....

http://www.scandoil.com/moxie-bm2/ne...e-vessel.shtml

Cheers.

[murdomack]

These new lifting vessels all seem to have cranes that do not have any counterweights but transfer all their loads into the bouyancy of the hulls, which seem to be mono in all cases.

Going back to the old lifting barges, 3/4000 tons max, some of the originals were converted tanker hulls, but most of them had extra bouyancy tanks extending their beams outwards. The later purpose-built ones were all twin hulls some with twin athwart-ship cranes and were lifting up to 11,700 tonnes (BP Clair). They had a beam of 85 mtrs and across the deck were over 100 mtrs wide.


I assume that the new vessels are relying on computer systems to keep them safe. Somehow, I think that there will be a lot of sleepless nights when heavy lifting is ongoing.

[mflapan]

Dear All

CFR 46 contains addtional dynamic balance criteria for crane vessels that rely on counter weights or counterballast during lifting operations.

These have been rewritten (hopefully with greater clarity) in the National Standard for Commercial Vessels Part C Subsection 6A Chapter 6F criteria. See page 50 in http://www.nmsc.gov.au/documents/NSCV/NSCV_6A.pdf

The criteria consider the effect of the hook load breaking while the vessel is using counter ballast/counter weights. The analysis considers the righting lever curve of the vessel without the hook load.

It would be interesting to know whether the vessels considered in previous posts apply such criteria, or whether they are applying other criteria, and if so, what they might be.

Regards
Mori

[safewalrus]

'Tis a well known fact that sea air and electronics don't mix very well, yet still they produce these monstrosities! OK for some time they will work, but one day something is going to fail!! Hope all the "experts" have their pencils ready for that day, 'cos sure as hell there's going to be some explaining to do - especially to next of kin!!

[Guillermo]

OK, here we are. Thanks for splitting, Jeff!

Mori,
As I told you, I have no data for such kind of boats and I'm willing to learn. I hope somebody will pop up with info.

The NSCV criteria asume lifting by the side but, do these big-craned ships lift by the side or by the stern?

Best.

[Guillermo]

I have found this:
"With the increased activity of the offshore oil and gas industry the demand for versatile construction vessels is increasing in terms of number, capacity and workability. Vessels are no longer designed for one specific purpose, but must be able to combine multiple tasks for improved efficiency. This demand for more versatile vessels has spawned a whole new generation of offshore construction vessels.

The combination of different tasks results in new problems and difficulties and forces the designers to come up with new innovative solutions.

A combination of missions that is becoming more and more accepted is that of pipelaying and heavy lifting. These vessels can be used for the installation of a topside module and continue with the installation of the subsea flow lines, completing the job without the need for separate vessels.

A problem with the pipelay / heavy combination is the trade off between the seakeeping characteristics required for pipelay operation and the demand for a stable platform for heavy lifting. Pipelaying requires a slender vessel with a large roll period, whilst for heavy lifting a wide stable platform is essential.

To meet these two requirements a hullform has been designed with two operational waterlines: 43.5 m for lifting operations and 36 m for pipelay operations. During pipelay operation the ship operates at a draft of 8.4 m, and for heavy lift operations the ships takes in ballast water and increases its draft until the waterline is at the maximum width of 43.5 m.

A motion analysis showed a significant increase in the ships operability especially when operating in beam seas where the operability in pipelay mode is increased from 30% to 90%. The average workability also increases which means that the ship will suffer less from downtime and can perform more efficiently.

From the study it can be concluded that the double waterline in principle is a promising solution for ships requiring both stability and good motion characteristics. For pipelay mode the benefits regarding workability are significant. The key to a good functioning design is the amount of ballast water that can be accommodated to ballast the ship. If the ballast capacity is limited the operational freedom of the lifting mode is also limited which reduces the functionality of the ship.

A potential problem is wave slamming at the transition between both waterlines when transiting or during pipelaying so further investigation is required."

http://www.tudelft.nl/live/pagina.js...2cf9a3&lang=en

Cheers.

[bear]

http://youtube.com/watch?v=WcU4t6zRAKg