SHANGHAI: The wreck of a 15,000-tonnage vessel that sank in the Huangpu River two months ago was salvaged yesterday, setting a national record for the number of external buoyancy floats employed in a river salvage.

The Yinchu, a 146.5-meter, 6,820-ton cargo ship, weighed about 7,500 tons under water. The ship was the largest vessel to capsize on Shanghai's Huangpu River since 1949. It sank on December 2.

"We used 10 pontoons and two floating cranes capable of lifting 8,500 tons. No previous salvage effort on a river has used so much lifting power before," said Wang Lei, a salvage expert with the Shanghai Maritime Bureau.

Before the accident, the ship was being converted from a roll-on-roll-off cargo vessel into a dredger at a dock just a few dozen meters from the Nanpu Bridge.

The Yinchu was suddenly flooded and capsized during its test launch. Local maritime authorities said a door had been left open, letting water in.

The half-submerged wreckage partly blocked shipping traffic on the busy waterway.

The salvage effort started on December 25, when divers punched holes in the ship's hull and passed steel cables beneath the wreck so it could be hauled up. "That was the most difficult part because the river bed is littered with large stones and abandoned steel panels," said Wang.

The Yinchu sank near an old coal-loading dock, so the stones were likely cast off by loading ships. There is also a shipyard nearby, which could account for the steel panels and cables on the river bottom.

"It is almost impossible to see beyond a depth of 18 meters, so our divers had to conquer the darkness and the complicated underwater conditions," said Wang.

The diving team eventually passed 30 steel cables through 11 holes, which they attached to 10 large-tonnage pontoons. Floating cranes were positioned at the ship's bow and stern.

But those were not the only difficulties.

"The water was so cold that the divers could only stay underwater for limited stretches. The large amount of traffic on the river also influenced the divers' work," he said.

The salvage cost an estimated 16.5 million yuan, which was to be paid by the ship's owner and maintenance company that had worked on the Yinchu. Part of the cost was related to the effort to clean up all the pollution caused by the wreck.

Officials from the Shanghai Maritime Bureau said they would inspect the wreckage to determine the cause of the accident.