Stormy weather forced a barge to collide with an oil tanker off the western coast of South Korea on Friday morning, puncturing the side of the tanker and causing the worst oil spill in the country's history. By Sunday, the South Korean coast guard said all three leaks in the tanker had been plugged. How do you seal a hole in an oil tanker?
First, wait until the oil stops gushing. Then, if it's a tiny hole, plug it up with cork, cloth, plastic, or pieces of wood. There's not much special knowledge when it comes to small openings: Just fill it with whatever material you have at hand and use a mallet to pound it all in. (If the damage is underwater you'll need divers to do this job.) This method can work even for gashes up to about ten feet long and two feet wide, although these situations might require patching together timber columns. In rare cases, the crew might instead use a sheet of magnetic material that functions like a giant refrigerator magnet, covering a hole on the side of the ship. In addition, concrete is sometimes used to plug holes.
Collisions like the one near South Korea can cause jagged craters that are dozens of feet long—too big to stuff up with a cork or cover over with a magnet. In the recent spill in San Francisco Bay, a container ship hit a major bridge and lost a chunk of its side that was 212 feet long and 12 feet wide. In these cases, divers or other repair workers would need to measure the hole, radio the dimensions to shore, and wait for a shipyard to create a steel patch of the appropriate size. Once the oil has stopped leaking, the patch can be installed. A crane would hold the steel plate in place while underwater workers bolted or welded it to the boat. (In 1989, divers reinforced the damaged bottom of the Exxon Valdez with rivets before the ship left Alaska for full repairs.) Welding can be dangerous, though, since volatile gases like butane and propane may be present in the tank. If workers decide to proceed, they'll take extra precautions like opening the air vents at the top of the tank so the gases won't accumulate.
Why wait for the oil to leak out before fixing the hole? It's very difficult to install a plug or patch while liquid is pouring out at high pressure. That means that patching usually takes place after the spill has stopped, though small amounts of oil can continue to leak as a tanker shifts in the current. (This is called "weeping.") The gushing might stop when so much oil has flowed out that the level inside the tank lies below the hole, possibly within hours of the initial breach. If emergency workers manage to reach the tanker soon enough after an accident, they'll start "lightering" the boat, that is, pumping the remaining oil over to another vessel. They might also attempt to shift the cargo around so that the boat lists away from the damaged side.
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Explainer thanks Capt. Richard Hooper of Naval Sea Systems Command, Robert Urban of PCCI, and David Usher of Marine Pollution Control.