Costa Concordia Salvage: Trouble at the Big Dents

Since the successful righting of the hulk Costa Concordia by Titan-Micoperi last fall, it's been said often that the most difficult part is over (photo, Parbuckling Project):

That world-famous parbuckling job was accomplished using strand jacks, cables, anchors, temporary steel supports on the seabed, and giant ballast tanks, called sponsons, mounted on the port side.

Though the most spectacular part is complete, I continue to believe that the work to get it off the rocks and into a breaker's yard in one piece will be very difficult and maybe more so than the parbuckling itself.

I'll explain the reasons below, but first this obscure, yet worrisome news item: Last week an 800-ton sponson tank (numbered S13) intended for the starboard side came loose from its fastenings shortly after being placed. Starboard means right side; that's the side facing the shore of Giglio, which was underwater for months until  the ship rolled upright.  

Sponson S13 had positive buoyancy at the time, and in rising out of control, collided with an adjacent sponson. Divers were underwater at the time but apparently no one was injured. 

The heavy-lift Conquest MB1 crane has since loaded Sponson S13 back onto the pontoon barge MAK and now it's back at Genoa for repairs (crane photo, Concordia Group):

As I explained in previous posts, the two sides of the ship present different engineering challenges. Most of the port-side hull was relatively easy to work during the parbuckling preparations, because it was completely exposed to view, and because it wasn't heavily damaged. At the time, the port was the "uppermost side" of the wreck and riggers could work on it while harnessed to safety lines.

Both sides of the ship need to have sponsons installed so the ship will float enough to get it off the rocks and temporary platform; therefore both sides must serve as supports for these giant tanks.

Even now that parbuckling has set the ship upright, the rusty starboard side is much more difficult to work on than the port side had been. For one thing, the starboard side of the hull lies underwater, so work must be done by divers. (The parts in view above the waterline are the superstructure).

Another reason for the current difficulty is that the starboard side sustained enormously more damage than the port side. That side supported the entire deadweight of the ship for months, and much of that stress was concentrated into two zones, fore and aft, where the ship lay on its side, supported mostly by a pair of underwater pinnacles. 

I call those damage zones on the starboard side the Big Dents. Here's a Reuters photo of the starboard side, after parbuckling:

Sponson S13 has to attach onto the dent to the left of the picture, near the aft end of the ship. Here's a Parbuckling Project photo of S13 being lifted into place:

Here's a side view, also from the Project:

The lower diagram in the sponson map below shows the starboard side. Look at the long green rectangle near the stern: 

Sponson S13 is the long green object, horizontally oriented, and it's the one that had the problem earlier this month. From what I gather, the hull at this spot is so dented that a vertical tank can't be secured, so it has to be horizontal instead. 

The official explanation of the recent breakaway of Sponson S13 is that a chain passing under the hull wasn't tight enough, and this slack caused one end of the sponson to lift and damaged another one nearby. There might be more to it; certainly the Big Dent is a very difficult area in which to work.

I hope this post gives a little context to the latest news reports from Titan-Micoperi. To summarize: the ship is severely damaged due to wave motion over the months since the grounding, and because of how the ship came to rest; sponsons need to be placed there anyway to get the ship off the rocks; and the attachment points to that irregular, weakened zone are problematic. The whole ship may be so weakened that it won't hold together under the strain.

So once the hulk lifts off the reef and begins moving (whether under tow, or being pulled onto a semi-submersible recovery ship), it's sure to be a tense time for the salvors.  

Here's my information request of the week: imagery showing the results of an underwater sonar or photogrammetric survey of the starboard side of Costa Concordia.