So I guess I don't really understand the situation in question... I heard a radio piece about the Costa Concordia shipwreck in Italy taking 7-10 months to remove the vessel from its place of resting, and I was reminded of the Donald-Duck-ping-pong-balls-solution for raising a sunken ship.
How come they're not using that solution in this case? (or is someone just forgetting about it?) Are there things about a very large cruise ship that would make the ping-pong ball solution impractical?
The Costa Concordia wasn't sunken, it was aground. Which meant that part of it was still above the water. The ping pong solution can only be used if the ship is completely underwater. Otherwise, it will have an opposite effect.
The buoyant force (force by which a fluid pushes up on a body, thus keeping it afloat), is proportional to the mass of the fluid displaced by the body. Thus, it can also be said to be proportional to the volume of the body that is submerged. Adding a ping pong ball to a floating ship will make it heavier, without changing the volume underwater (OK, it will sink a bit, changing the volume underwater, but that doesn't help us). Adding a ping pong ball to a ship that's aground has no use whatsoever.
On the other hand, a ship that is underwater is full of water. Adding a ping pong ball to the ship will force out some water, $\implies$ more water displaced $\implies$ more buoyant force. The reason this is better than pumping air is that air can easily excape, ping-pong balls can't.
Adding a ping pong ball here would just make it float inside the ship. It wouldn't displace any water.
Ping pong balls can stand the pressure. They crush at about 476 meters depth of water so no problem there. The ping pong balls could be pumped into each submerged compartment. They would displace the water provided the compartment doors could be sealed quickly enough to keep the balls from floating out. From my understanding the ship was damaged from hitting a rock outcropping and that damage is above the waterline so repairs should be possible. The problem of the ship being "aground" should be overcome by removing the fuel, the water, and emptying the ballast tanks if there are any. To me the greatest problem would be making the ship float upright and not capsize in the process of re-floating it. Those cruise ships look so very top heavy to me.
fill the emptied fuel tanks with the balls. the ones they pushed sea water into to get the fuel out.. that in it's self has to be a huge amount of displacement and should allow the ship to float once again. Just like in diving there would have to be a way to let some of displacement out as not to rise to fast and flip the ship. Diving 101. Inflate BCD to surface. as you rise let some of the expanding air out of the BCD as not to rise to fast. Keeping in mind that other compressed objects IE: Cushions will become more buoyant as the ship rises. there also has to be laser guides along the hull of the ship to make sure it doesn't twist. and the ship looks so close to the shore you could use a couple of cranes to attach to the top of the ship to make sure it stays upright as it is raised. An even better idea is to use that expanding foam crap. the same stuff they shoot under houses to and concrete to level them. it will cure under water. stays where you put it and expands an extreme amount displacing a lot of water.
anchor the vessel near the bottom, tug it upright (make sure you secure the vessel from listing the opposite direction), patch hull, pump out the water, tow home, airbags can lift the vessel once its upright to the waterline where it can be pumped out
