In a race against time, rescue divers resumed on Sunday the search of the stricken Costa Concordia cruise liner. They retrieved the body of a woman wearing a life jacket, thus bringing the number of people confirmed dead to 13.

Nine days after the 114,500-ton ship ran aground off the Tuscan coast of Giglio island with more than 4,200 people aboard, the number of passengers still unaccounted for remains uncertain.

"The liner may have been carrying unregistered passengers," Franco Gabrielli, the head of the Civil Protection Authority, said at a news conference on Sunday.

"We are determined in continuing the search, but at the same time we must prevent an environmental disaster. A scientific and technical committee will report on the next steps by the end of the day," Gabrielli said.

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As Dutch workers of the Smit Salvage company are preparing to drill into the ship's fuel tanks and pump out 2,300 tonnes of fuel oil, experts are also considering anchoring the ship to the reef to prevent it from sinking.

The fuel recovering operation is expected to last two to four weeks, most likely amid rough seas.

This might pose a serious threat, according to experts. The ship has continued to shift dangerously and has now reached an inclination of more than 80 degrees. A picture in the daily paper Il Tirreno clearly shows the dramatic change in the inclination within six days.

"Overnight, sensors recorded a shifting at a rate of about 0.39 inches an hour, but now the good news is that the ship hardly moves. We can't say whether this condition is going to last or not," said Nicola Casagli of the University of Florence, who is monitoring the ship's stability.

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If the wreck moves from its precarious resting place, it might reach the point in which the sea floor drops off sharply to a depth of about 290 feet, possibly rupturing the tanks and spilling almost 500,000 million gallons of heavy fuel into the pristine waters of the Tuscan wildlife sanctuary.

The island of Giglio lies within the Pelagos Sanctuary for Mediterranean Marine Mammals, and is home to more than 700 botanical and animal species including fin whales, sperm whales, dolphins, tuna, billfish and sharks.

According to Giuseppe Bocci, an architect at Bocci and Partners, a company working in the field of architecture, civil engineering, town planning, 21 steel ropes are necessary to chain the Concordia to the reef.

The project would involve "slinging" the Concordia with 4-inch-diameter steel ropes, anchoring them both to the reef and the sea bottom.

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"It the same principle of the floating tension leg platforms. There, the mooring system consists of tendons, or tension leg, attached to the structure and connected to a foundation on the seabed," Bocci told Discovery News.

"Obviously, there is no time to build fondations, but a decent number of anchors would work in securing the ship," Bocci said.

He estimated that the project , if ever approved, could be realized in about two days.

Meanwhile, no fuel oil has yet leaked from the ship, Gabrielli said. He also reassured that tests for toxic substances "are negative so far."

"The only significant elements detected relate to detergents and disinfectants used on the ship – all things that a floating city of 4,000 people need," Gabrielli said.

Image: A proposed project to chain the capsized Costa Concordia luxury liner. Credit: Bocci and Partners


Video: Waste has begun to leak from the Costa Concordia cruise ship.