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Author Topic: Floating Off  (Read 8210 times)

BarryM

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Floating Off
« on: August 15, 2010, 02:08:06 pm »

Whenever I see something like this I'm glad I'm not responsible for the stability and ballasting calculations.

Barry M

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Bryan Young

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Re: Floating Off
« Reply #1 on: August 15, 2010, 09:32:40 pm »

This is something that's been bothering me for a few years now. I know from a tug-master pal of mine that the carrying ship can go down to about 40ft draught. But that still, in my mind, doesn't seem to be enough to compensate for all that top hamper. I suppose it must, otherwise none of it would work! Like you, I've tried to work out a hypothetical stability problem with all that, and I always come up with everything floating upside down. Bryan.
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Notes from a simple seaman

BarryM

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Re: Floating Off
« Reply #2 on: August 15, 2010, 10:36:28 pm »

With that level of reserve buoyancy, you get the feeling that a deck landing by a flock of moderately heavy seagulls would lead to a sudden gurgling and a large insurance claim.

Cheers,

Barry M
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Bryan Young

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Re: Floating Off
« Reply #3 on: August 16, 2010, 02:26:19 pm »

With that level of reserve buoyancy, you get the feeling that a deck landing by a flock of moderately heavy seagulls would lead to a sudden gurgling and a large insurance claim.

Cheers,

Barry M
Barry, if your'e referring to the reserve buoyancy as shown in your photo, then that's a bit misleading. The rig is being "loaded", and so the carrier ship is docked down far enough for the rig to be floated over it. It will rise considerably when the rig is in position, thus giving extra buoyancy. The stability problem is still a closed book to me though!. Bryan.
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BarryM

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Re: Floating Off
« Reply #4 on: August 16, 2010, 03:09:52 pm »

Bryan,

The Photo is of 'Noble Jim Day' off-loading from the 'Blue Marlin' near Curacao but, coming or going, my reference was to the reserve buoyancy that is left while the operation is taking place. Precious little, I suspect!

Hairy!

Barry
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Dave Buckingham

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Re: Floating Off
« Reply #5 on: August 16, 2010, 05:37:56 pm »

The reserve buoyancy is very little I agree but that is not much of a problem.

As has been said the Stability on the way up and at sailing draft is the dodgy think I would love to see the calculations,

As long as I did not have to do them even if I remember how

DDave
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Prophet

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Re: Floating Off
« Reply #6 on: August 16, 2010, 05:41:59 pm »

stability during loading of these huge crafts is helped by extending telescopic legs that come from under the boats hull there homes are the large tower at the rear left side and one at the front by the superstructure they extend down and touch the sea bead aiding it its stability during loading and during heavy weather,(was on Mighty ships on discovery recently)  admittedly during transport its pretty dodgy floating that much mass out to sea.

but heres some more pics of some other stuff that these massive boats can lift along with the stats for the Blue Marlin in case anyone intrested

Original specifications:
Length Overall: 217 m (712 ft)
Length PP: 206.5 m (677 ft)
Breadth Moulded: 42 m (138 ft)
Depth Moulded: 13.3 m (44 ft)
Summer Draft: 10 m (33 ft)
Deadweight: 56,000 metric tons (USS Cole weighed much less than 8,000 metric tons)
Submerged Depth above Deck: 10 m (33 ft)
Free Deck Length: 178.2 m or 157.2 m (585 ft or 516 ft)
Free Deck Area: More than 7215 m² (77,672 ft²)
Main Engine Output: 12,640 kW (17,160 BHP)
Bow Thruster: 2,000 kW (2,712 BHP)
Cruise Speed: 14.5 knots
Cruise Range: 25,000 nm
Accommodation: 55 people
Building Yard: CSBC, Kaohsiung

Post-2004 specifications:
Length Overall: 224.5 m (736 ft)
Breadth: 63 m (207 ft)
Depth: 13.3 m (44 ft)
Max sailing draft: 10. m (33 ft)
Max draft submerged: 29.3 m (96 ft)
Water above deck submerged
              - aft 16 m (53 ft)
              - forward 12 m (39 ft)
Deadweight: 76,060 metric tons
Deck space: 63 x 178.2 m (207 x 585 ft)
Deck area: 11,227 m² (120,850 ft²)
Propulsor output: 4500 kW (6,035 hp) each
Conversion yard: Hyundai Mipo Dockyard, Ulsan, South Korea













But when it goes wrong.... this is the outcome!!








sorry post is long winded but i though it was all relevent to the subject


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Bryan Young

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Re: Floating Off
« Reply #7 on: August 16, 2010, 06:29:05 pm »

Prophet, for heavens sake don't apologize for such an educational post.
I imagine that "things" going wrong are few and far between, but pretty catastrophic when they do.
I guess that even now in my dotage I could work out the stability when carting around a frigate or something similar, but it's those rigs that get through to me. My mental processes seem to come to a halt when I try to imagine where the Centre of Gravity of the rig is. That doesn't change. So assuming (?!) the CG is maybe 60ft or more up from the rigs bottom, that has to be added to the CG of the carrying ship. Which to me moves the "mass" CG of the combined units somewhat higher than the normal "staying upright" level. So why doesn't the whole thing just topple over? I'm obviously wrong otherwise that would happen. Confusedly, BY.
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MikeK

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Re: Floating Off
« Reply #8 on: August 16, 2010, 08:12:40 pm »

One thing is for sure - destroyer turns definitely a no-no !!  O0 :embarrassed:

Mike
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Prophet

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Re: Floating Off
« Reply #9 on: August 16, 2010, 08:29:27 pm »

im not much of a super mathmatical person but to me it would suggest that the boats dont topple over because of the overall weight of the object on the top . take the rigs for example they must hang over a good few feet over the sides...

imagin... try to put this into words... counter balance of the structure sat on the boat ...need a pic for this one...

Ok try the maths on this one if im wrong im wrong but i think this is how it works

A (wave/Wind) pushed on B, B transfers to C, ( boat sways) Weight of B counteracts the the force of A moving C back to normal.. err i think thats right...

basically the same as a skyscraper's counterbalance for winds, without the use of a few ton gyro!

See if the pic helps!

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DickyD

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Re: Floating Off
« Reply #10 on: August 16, 2010, 08:40:33 pm »

No.
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Prophet

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Re: Floating Off
« Reply #11 on: August 16, 2010, 08:43:00 pm »

perfect im just as confused as the rest of you ...  :embarrassed: :embarrassed: :D :D :-))
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gondolier88

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Re: Floating Off
« Reply #12 on: August 16, 2010, 09:59:26 pm »

Must be magic!

Interesting to note in your last pic there Prophet, the funnel on the port side still has smoke issuing from it, these ships must have some serious watertight compartmentalisation!

Greg
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bosun

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Re: Floating Off
« Reply #13 on: August 16, 2010, 10:00:53 pm »

Hy Guys
If you look at the size of the bridge windows on the ship carrying the rig, the one with the coastline in view, and then imagine the size of the men behind them windows in comparison to the actual lift/cargo that the ship is carrying, that is absolutely awsome.
 Great post and pics, nice one prophet.
Bosun
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RaaArtyGunner

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Re: Floating Off
« Reply #14 on: August 16, 2010, 10:36:37 pm »


 Great post and pics, nice one prophet.
Bosun
O0 O0 :-)) :-))
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BarryM

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Re: Floating Off
« Reply #15 on: August 17, 2010, 09:16:07 am »

Prophet,

Are you sure about the extendable stabilising legs? The square structures at the stern are usually removable, auxiliary, ballast tanks and I can't identify the for'd structure you refer to.

Cheers,

Barry M
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Prophet

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Re: Floating Off
« Reply #16 on: August 17, 2010, 09:57:25 am »

I'm 100% positive on the legs i was watching it on discovery a few days ago (mighty ships) when they were loading the ship with mega yachts i don't think the boat was the Blue Marlin it was a sister ship of some sort but the legs are there, i will try to find an article about them ...

this is the dockwise yacht transporter that has them..( what the program was talking about)
http://www.yacht-transport.com/homepage.html
i have looked for the part about the legs and cant find proof but i swear that's what the TV program said!
hopfully some one else will have seen that episode and will confirm what I'm saying
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Prophet

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Re: Floating Off
« Reply #17 on: August 17, 2010, 10:35:47 am »

Some semi-submersible vessels are designed with a pair of parallel horizontal pontoons, which support vertically extending columns. Other designs provide for the use of the so-called “ring pontoon,” which is not necessarily circular. In most cases, the term “ring pontoon” is applied to square or rectangular pontoons that are defined by four interconnected pontoon portions. The object of the pontoons is to facilitate stability of a vessel in deep waters.

U.S. Pat. No. 4,907,912 illustrates another example of a jack-up rig using a submersible storage barge. During transit, the submersible storage barge-provides the flotation means for the rig hull. Once the unit reaches the drill site, the submersible barge is lowered together with the support legs until they rest upon a sea bottom. The submersible barge is at least flooded to stabilize its position on the sea bottom.

It is another object of the invention to increase the added mass of the unit in a simple and cost effective way by using the second tier pontoon (STP) in the ESEMI. ESEMI allows the added mass of the vessel to be increased without any increase of displacement, as would be the case with conventional semi-submersibles designs. Instead of increasing the displacement to achieve higher added mass, this invention seeks to separate the total displacement into two different locations in the operation mode. One part of this displacement is located in the conventional semisubmersible hull and the other part, called STP, is situated at a certain distance below the hull. This separation of the total displacement results in higher overall added mass for the ESEMI compared to the conventional semi-submersible of similar displacement.

The major wave- and current-influenced forces act on the columns and the pontoons at the upper levels below the sea surface. These forces normally decrease with increasing depth below the surface. The vessel of the present invention provides for the use of a two-tier pontoon system. An upper ring pontoon supports stabilizing columns, which in turn support the upper hull and the deck structures. The lower pontoon moves vertically in relation to the upper pontoon through the use of an independent ballasting system housed in the lower, or second tier pontoon. By dropping the second tier pontoon (STP) to a depth well below the sea surface, preferably below the most strongly wave-influenced zone, the semi-submersible unit of the present invention achieves motion response characteristics normally only achieved by large purpose built fixed units.

According to a preferred embodiment of the invention, the second tier pontoon supports a plurality of vertically movable retractable legs. The legs move through leg guides carried by exterior of the stabilizing columns and the upper pontoon. The legs ensure that the second tier pontoon is retained in a parallel relationship to the upper pontoon.

When in transit, the lower buoyant pontoon is secured in close proximity to the upper pontoon, and the legs are fully retracted. Once the vessel reaches the operational site, the second pontoon is ballasted and lowered such that the upper pontoon baseline is about 32 meters above the second tier pontoon baseline. The second tier pontoon remains locked in relation to the upper pontoon and the upper hull through a series of winches tensioning handling lines, which connect the second tier pontoon to the main deck.

Took these quotes from the US paintent office about the telescopic legs.

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BarryM

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Re: Floating Off
« Reply #18 on: August 17, 2010, 11:41:01 am »

Prophet,

There's some confusion here between the designation 'semi-submersible' as a type of vessel when applied to transport barges, (Mighty Servant etc.), SWATH twin-hulls with column-supported decks (drilling units, accommodation units or SSCV) and the description you have given of what appears to be a proposed jack-up design for a drilling unit with upper and lower hulls. The latter resting on the seabed and the former jacked up above the surface.

Jack-up rigs are commonly dry-transported by bringing the transporting vessel between the legs and below the operating deck. The operating deck is then jacked down onto the transport and elevation of the legs continues until they are sufficiently retracted to permit the transport to commence.

Barry M   
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Prophet

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Re: Floating Off
« Reply #19 on: August 17, 2010, 11:43:10 am »

found some more pics of when things go wrong, from what i have found out, Dockwise have lost 2 vessles over recent years once through accident, (it hit something on the sea bed) the other was caused by human error resutling in the capsizing of one of the mighty servant 3 in 2006. it just goes to show how far on the edge we are willing to go to move things that big it basically boils down to a 50/50 chance of sucsess ...  not good odds for any company wanting to move such an item!








general images of other lifts everone seams to love these pics



on the cost side i have found out that to hire the use of one of these is $500,000 a day + fuel! it takes 10 hours to flood the boat fully to take a load so theres $1,000.000 gone already!
up to 18 days for the trip, and a 2 for depositing the load.... 22 days at a cost of $11,000,000
 
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BarryM

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Re: Floating Off
« Reply #20 on: August 17, 2010, 10:05:56 pm »

I checked with them what should know and they confirmed that heavy-lift transports with steadying legs were unknown to them. The best they could come up with were wind turbine installation vessels that sometimes had jack-up legs.

Cheers,

Barry M
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Prophet

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Re: Floating Off
« Reply #21 on: August 17, 2010, 10:47:00 pm »

im at a loss to what to say about that although it was on tv? if anyone has access to the mighty ship programs look for the episode about the super servant that will confirm what i have said other then then its just a myth i guess  >:-o
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amdaylight

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Re: Floating Off
« Reply #22 on: August 18, 2010, 02:20:05 am »

Prophet,

I have also watched these shows and amazed at how much bad, misleading and just plain Bulls**t they put out. These range from using the wrong term to just plain wrong. They also seem to get things mixed up from one show to the next. I some times want to write them and let them know where they went south but then remember that some of these shows are 3 or 4 years old. So don't I don't worry about it and just enjoy the show as it beats Oprah. %%

Andre
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Bryan Young

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Re: Floating Off
« Reply #23 on: August 18, 2010, 07:18:22 pm »

Was this thing ever raised? It just seemed to have succumbed to BarryMs idea that a flock of seagulls may have landed just at the wrong time.
As far as that nicely drawn idea of the bottom bit acting as a pendulum is concerned....well, when floating in a fluid, and ignoring the actual weight of what's going from side to side above your head is a recipe for disaster. The centre of Gravity of an object (like the rigs illustrated) will move as it "tilts" (or rolls), so the "low" side will be the heavier as far as "leverage" is concerned. So you get a turning "moment" that can only be counteracted by a stronger counteracting lever (or moment). So. Sorry. Your take one a ships stability gets you a basic "0 out of 10". Please try harder! But I still don't have a full answer. BY.
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farrow

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Re: Floating Off
« Reply #24 on: August 22, 2010, 10:19:46 pm »

I expect the stability programme is not much different to a floating drydock. The secret is to get the centre of gravity of the object to be lifted over the centre of bouyancy the lifting vessel and ensuring that the end GM shows positive bouyancy. Much the same when lifting a heavy lift onto a standard hull as deck cargo.
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