During an online press conference today out of Pearl Harbor, Hawaii, the U.S. Navy detailed the operational procedures for removing the bodies of the crewmembers trapped in the hull of the sunken Ehime Maru. According to official reports, the humanitarian mission is “the most challenging recovery effort the Navy has ever undertaken.”
The Japanese training and fishing vessel sunk on Feb. 9 when a Los Angeles class submarine, the USS Greeneville, collided with it outside of Hawaiian State waters, south of Diamond Head, Oahu. At the time of the sinking, 26 of the 35 people aboard were rescued. Some 10,000 gallons of diesel fuel may also still be aboard, creating a major environmental concern the Navy is preparing to handle. From mid-August possibly through October, they will attempt to lift the vessel from 600 meters and transport it at depth to shallower waters.
“Had this occurred 15 years ago we would not have been able to undertake this operation because the technology simply did not support it,” said Rear Adm. William Klemm, recovery operation commander.
The Navy plans to raise the damaged, 750-metric ton ship, above the seafloor using modern oilfield drilling equipment. Then they will transport the ship 20 kilometers to a recovery site in 35-meter-deep waters closer to shore. Relying on Remotely Operated Vehicles (ROVs) and other ocean science technology for guidance.
“We think we have about an 80 percent chance of hitting it on the money,” Klemm said.
The 20 percent of doubt comes from not being able to determine the full extent of the ship’s structural integrity, he says. Ehime Maru sits with a five-degree starboard list, leaning to its right, in soft sediment underlain by clay. Much of the expected damage is hidden from view.
To lift and transport the Ehime Maru from the seafloor, the Navy will first drill two tunnels (350 millimeters in diameter) through the sediment. They will then pull messenger lines on the other side back through the tunnels and attach the lines to high-strength wire ropes on the ends of two lifting plates (20 meters by 1.5 meters by 19 millimeters). The ropes will then pull the plates under the ship. Water jets on the plates will also help push the plates through the sediment.
The coiled tube drilling system is operated from the surface with the drilling head positioned on the seafloor. The drilling equipment is “common oilfield technology today,” Klemm said. But, “it’s never been used submerged at 2,000 feet. So how it reacts under 60 atmospheres of pressure is going to be the question.”
The Navy will lift the ship about 30 meters from the seafloor and inspect it using two video-equipped ROVs. This will be the telling point of the operation and holds the greatest risk for oil leakage. “Once we move the ship, if we stand it right up or if we lift it the other direction, now that oil has a different flow path,” Klemm said.
Oceanographic buoys from Texas A&M University used to track oil spills in the Gulf of Mexico will monitor current speeds, direction and temperature. At depth, an estimated 65 percent of any diesel fuel released would be mixed into the water column and diluted to non-hazardous levels within five hours. The lubricating oil used on the Ehime Maru is more persistent in the environment, but very little of the 4,500 liters is thought to still be aboard. In any case, the Navy is prepared with booms, skimmers, sorbents and dispersant capabilities.
Moving the ship will then depend on the weather. The needed conditions include 15-knot tradewinds, favorable currents to help steady the ship and an outgoing tide to prevent any oil spills from entering either Pearl Harbor or Kaidi Lagoon and the downtown area of Waikiki. Also, the wave swells from the Southern Hemisphere and wind-driven waves will need to be low enough to handle the move. “The lifting sequence calls for raising the ship at approximately one meter per minute,” Klemm said. As the currents at the surface are different than they are at depth, the fastest the ship can travel toward the Reef Runway recovery site, and maintain a depth of 30 meters above the seafloor, is one knot, or one nautical mile per hour.
“If everything works the way we would expect it to mechanically, we may still have to sit and wait for the weather to match,” Klemm said. And according to the Navy’s Environmental Assessment Report: “This recovery operation is not without risks, and there is no guarantee of success.”