The capsized 15,000-ton Yin Chu has been awaiting salvage in the Huangpu River. A crack team of divers will begin work on Monday, and the job is expected to last 45 days.

A dozen of the most skilled salvage divers have arrived in Shanghai to raise a 15,000-ton ship that capsized in the Huangpu River.

The huge operation will begin today, the Shanghai Salvage Bureau said Sunday.

The roll-on-roll-off cargo vessel, Yin Chu, sank when berthing by a dock near Nanpu Bridge on December 2.

The bureau said the salvage operation will be very challenging and is expected to take about 45 days if not interrupted by cold fronts or strong tides.

The Shanghai Maritime Safety Administration said it will closely supervise the salvage operation to ensure water and shipping safety.

The Yin Chu capsized in a busy and narrow waterway off the Shanghai World Expo site apparently after a door was inadvertently left open.

An underwater investigation on December 10 showed that the ship's bottom is buried two meters in silt on the river bed, while divers found waste, mainly iron scraps and steel wires, entangling the wreck.

The divers also discovered 10 holes, ranging from seven to 10 square meters, on the deck, filling the vessel with water and silt.

These conditions will make the salvage operation even more tricky.

The vessel is estimated to weigh about an extra 7,500 tons in the water now, according to salvage experts.

Frogmen will have to dive more than 20 meters to clear the waste surrounding the vessel to make way for salvage work. They will then use high-pressure water guns to break up the silt burying the ship bottom so steel cables can be laid in a bid to stabilize the vessel.

The divers are expected to spend about 30 days working underwater to lay 20 cables, each 1.07 meters wide, through the ship's bottom.

The cables will all link to five pairs of floating canisters. It will take another 15 days for salvagers to finally pull up the wreck after all the cables are set in place.

Salvage equipment arrived at the scene on the weekend and the divers and supporting workers are ready to start.

The ship's five owners and the company working on refitting the vessel at the time of the accident signed a contract on Thursday hiring the Shanghai Salvage Bureau for the operation.

After mediation from the Shanghai Maritime Safety Administration, the salvage bureau agreed to cut its service fees by 40 percent for the job.

Insiders said the salvage program will cost less than the earlier forecast of 20 million yuan (US$2.55 million).