‘I’ve never seen a vessel this size go down so quickly’: why did the Bayesian sink in 60 seconds?

In the photograph, the luxury yacht Bayesian is peacefully anchored in the calm waters of Porticello bay, its 75-metre (246ft) mast towering above it. But on the horizon, dark clouds loom. The picture was captured last Sunday night by the owner of a restaurant in Porticello, a fishing village just a few kilometres from Palermo, Sicily. It was one of the last taken of the sailboat before it sank in a violent storm, killing the British tech entrepreneur Mike Lynch and six other people, including his 18-year-old daughter, Hannah.

Related: Mike Lynch yacht: possibility of manslaughter charges as final body found

Once described as Britain’s Bill Gates, Lynch was at the beginning of a new life , after being cleared in June of fraud charges in the US relating to the purchase of his company, Autonomy , by Hewlett-Packard in 2011. The tycoon opted to celebrate in style in Italy alongside Hannah, and his wife, Angela. They were joined by eminent figures including Lynch’s attorney from Clifford Chance, Chris Morvillo, and Morgan Stanley International’s chair, Jonathan Bloomer, along with their respective spouses and other associates. They were enjoying a lavish voyage around Sicily onboard the luxurious, British-flagged Bayesian, a magnificent 56-metre (184ft) sailboat named after 18th-century mathematician Thomas Bayes, whose work on probability informed Lynch’s professional thinking – in a violent storm off the coast of Sicily.

The yacht had set sail from Rotterdam in the Netherlands. Last week, it crossed the strait of Gibraltar, arriving off the coast of Sicily for a visit to the Aeolian Islands. Following a stop at the port of Milazzo on Sunday, 18 August, the Bayesian arrived off Porticello after a day spent off the shores of Cefalù, remaining at anchor, 500 metres (547 yards) from the port of Porticello.

Fabio Cefalù, 36, a local fisher, told the Guardian how the residents of Porticello, who are used to the sight of large tourist yachts, were impressed by the Bayesian, speculating that “it could belong to a Hollywood star or even to Elon Musk”.

Despite forecasts predicting an approaching storm, Cefalù had chosen to wake up in the middle of the night for a fishing trip. When he arrived at the port at 3.30am, the first flashes of lightning illuminated the sky.

“At 3.55, a sort of mini-tornado arrived,” Cefalù said. “I have seen many storms in my life. But I had never seen anything like this. I saw the wind sweep the chairs and tables of the bar, heading towards the boats in the harbour. The docks diverted the whirlwind, which went straight towards the yacht.’’

Related: Sicily yacht sinking: how do waterspouts form and what risk do they pose?

Onboard the Bayesian, the situation was beginning to deteriorate. The sailboat swayed dangerously at the mercy of the wind and waves. Located approximately 150 metres (492ft) away from the Bayesian was the Sir Robert Baden, a Dutch-flagged sailing ship built in 1957, and captained by the experienced sailor Karsten Borner, 69.

“We were awakened by the storm,” Karsten told the Guardian. “The first thing I did was to start the engines of my sailboat to give more stability to the vessel. After securing our boat, we immediately approached the Bayesian.’’

A photo obtained by the Guardian from a local fisher showed the moment a red emergency flare was launched from the Bayesian’s life raft at 4.35am.

Francesco Lo Coco, who took the image, said: “I saw the sailboat rocking. The emergency rocket was launched while the sailboat was already sinking.”

Borner was the first to attempt providing assistance to the Bayesian, but the boat was already going under.

“I have never seen a vessel of this size go down so quickly,” said Borner. “Within a few minutes, there was nothing left. Then we saw the raft with the 15 passengers. It was a tragedy.”

From a video taken by surveillance cameras at a shipyard , it seems the passengers of the Bayesian had about 16 minutes to save themselves and avoid the sinking.

According to the Italian news agency Adnkronos , which talked to sources among the authorities, the “passengers sought escape routes, reaching the opposite side of the vessel they were in”. But the water had already reached the cabins. The ship apparently sank bow first, and then slowly capsized on to its right side.

The day after the news broke, it made headlines across major Italian newspapers, reporting 15 survivors out of 22 passengers. However, late on Monday morning, when Italian authorities confirmed Lynch and his guests were among the seven missing , the tragedy quickly captured global attention.

At least 10 survivors were transported to the hospital, including Charlotte Golunski, 36, and her one-year-old daughter. She told doctors she had kept her child afloat by outstretching upwards her arms to prevent her from drowning.

Fishers in Porticello who witnessed the Bayesian sink rapidly say that the vessel was in the wrong place at the wrong time. But for Italian prosecutors investigating the incident , their focus is whether the captain and crew took all the necessary safety measures to prevent the tragedy.

Investigators from the nearby town of Termini Imerese have questioned all the survivors who were transferred to the Domina Zagarella hotel, guarded by security personnel. Prosecutors are investigating potential manslaughter charges .

Experts are baffled by how the Bayesian sank within 60 seconds. Italian media, speaking with coastguard sources, reported that a hatch allegedly remained opened and that the keel was partially raised. Some experts speculate that the crew may have underestimated the weather bulletin.

Gabriele Bruni, a sailor who has twice participated in the America’s Cup and has coached the Italian Olympic team, said: “If they had asked me that night, in a stormy day, in which sailboat in the world I would have wanted to be, I would have chosen the Bayesian.”

Search efforts begin immediately, in the early hours of Monday, with divers from the fire brigade working non-stop. Recovering the bodies was not simple.

“The greatest challenge is the depth,’’ Marco Tilotta, the head of the firefighter divers in Palermo, told the Guardian. “We have three minutes to descend and eight minutes to work on the wreck. Then we have to begin the ascent phase. Not to mention the furniture that blocks access to the cabins”.

The first body to be recovered was that of chef Recaldo Thomas on Monday afternoon. Two more bodies were recovered on Wednesday morning, those of Bloomer and Morvillo . In the afternoon, their spouses Judy and Neda were also found.

Mike Lynch’s body was found in the evening and transported to the dock in Porticello. On Friday divers recovered the body of Lynch’s daughter Hannah, the seventh and final victim.

Just like her father, the young woman had every reason to celebrate that night: her A-level results last week secured her a place to study English at Oxford University.

Just like her father, Hannah found herself at the outset of a new chapter in her life. A life abruptly interrupted one summer night by a tragedy that Italian investigators are now working to understand.