PORTICELLO, Italy(Reuters) - The recovery of British tech tycoon Mike Lynch's superyacht from the waters of northern Sicily is expected to begin in the coming weeks to help shed light on how a supposedly unsinkable vessel disappeared into the sea last August.

The 56-metre-long (184-foot) Bayesian, with its majestic single 72-metre mast, was moored off the small port of Porticello when it was likely hit by a downburst, a very strong downward wind, in the early hours of August 19.

The Bayesian capsized and sank from the stern in the space of 16 minutes, killing seven people, including Lynch and his daughter Hannah. Since then, the ship owned by the Lynch family has been lying on its starboard side at a depth of 49 metres.

The other six passengers, including Lynch's wife Angela Bacares, and nine crew members survived.

The tragedy has attracted international attention because of the fame of Lynch, known as "The Bill Gates of Britain".

The shipwreck has also puzzled naval marine experts.

The 534-tonne Bayesian, built in 2008 by yacht manufacturer Perini Navi, now owned by the Italian Sea Group, should have withstood the storm and, in any case, should not have sunk as quickly as it did, experts say.

MAST TO BE CUT BEFOREHAND

Italian prosecutors, who are investigating the yacht's captain and two other crew members for potential manslaughter, said their investigation will not be completed before the ship is lifted and inspected.

They summoned lawyers for all parties involved and technical advisers to Porticello on Wednesday to oversee a salvage operation expected to take 20-30 days.

"I don't think (the lifting) is going to be decisive for the investigations, but it's certainly important," said Mario Bellavista, a lawyer for the family of Recaldo Thomas, the onboard cook who died in the shipwreck.

He told journalists in Porticello that raw data from on-board equipment that has already been extracted from the wrecked yacht, including video surveillance cameras and navigation systems, will be shared with lawyers in June.

The consortium picked to salvage the yacht, led by UK-based consultancy TMC Marine and featuring a joint venture between Dutch companies HEBO Maritiemservice and Smit Salvage, plans to cut the mast before raising the vessel.

Preparatory works are already being conducted offshore from a 700-square-metre floating platform. An underwater robot is surveying the Bayesian, whose tanks contain 18,000 litres of diesel.

The vessel is expected to be brought to the surface by HEBO Lift 10, one of Europe's most powerful floating cranes, and then taken to Termini Imerese, about 40 kilometres east of Palermo.

HUMAN ERRORS OR DESIGN FLAWS?

The CEO of Italian Sea Group, Giovanni Costantino, blamed the sinking on a series of "indescribable, unreasonable errors" by the crew, and ruled out any design or construction flaws.

"The impossible happened on that boat ... but it went down because it took on water. From where, the investigators will tell," he said in an interview with Reuters in August. 

According to a prosecutors' document seen by Reuters, the night watch crewman, Matthew Griffiths, is suspected of failing to notice the worsening weather conditions, while the other sailor under investigation, Timothy Parker Eaton, was allegedly late in spotting that the boat was taking in water from the back. 

Both did not promptly warn Captain James Cutfield, who, in turn, is suspected of not taking all the necessary measures to deal with the emergency and not adequately warning passengers of the danger.

The three suspects have not commented publically on the allegations.

Another yacht that was anchored near the Bayesian survived intact.

Karsten Borner, the captain of that vessel, said the Bayesian flipped on its side and sank within minutes.