The owner and crew of a luxury superyacht that sank off the coast of Sicily, killing tech entrepreneur Mike Lynch and six others, were unaware wind speeds of over 73mph could tip it over, according to an interim report.

Modelling commissioned after the disaster indicates gusts of that speed hitting the side of the Bayesian, when it had its sails down and centreboard up, would “likely result” in its capsize.

The UK’s Marine Accident Investigation Branch (MAIB), leading the international investigation, said winds of over 80mph “violently” hit the vessel, causing it to flood within seconds.

It sank near the town Porticello on 19 August last year during freak weather, with reports of water spouts.

Seven of the 22 people onboard were killed, including Mr Lynch, 59, and his 18-year-old daughter Hannah.

Investigators say the yacht was knocked to a 90-degree angle within 15 seconds at 04:06 am local time, causing people, furniture and loose items to fall across the deck.

“There was no indication of flooding inside Bayesian until water came in over the starboard rails and, within seconds, entered the internal spaces down the stairwells,” the report says.

The MAIB’s chief inspector of marine accidents Andrew Moll said the situation was “irrecoverable” once the yacht tilted beyond 70 degrees.

The yacht had its sails down and centreboard up when it sank.

The MAIB commissioned modelling from the University of Southampton to examine the stability of the yacht in these conditions.

It indicated that – if the wind was blowing directly across the beam, or side, of the boat – wind speeds in excess of 73mph were sufficient to tip the boat over and “it is possible” the yacht was similarly vulnerable to lower wind speeds, the MAIB said.

But this information was not included in the onboard stability information book and “consequently, these vulnerabilities were also unknown to either the owner or the crew of Bayesian”, the report found.

The MAIB is investigating the incident as the Bayesian was registered in the UK. No date has been set for when its final report will be published.

It said its report was based on “a limited amount of verified evidence” as a criminal investigation by Italian authorities has restricted access to the wreck.

An operation to raise the 56-metre vessel from the seabed was paused over the weekend after a diver died while working on the wreck. Work was set to resume on Thursday.

The report lays out more detail as to how the sinking unfolded.

Investigators say the yacht sailed to the site where it sank on the previous day, in order to “shelter” from forecast thunderstorms. The sails were furled at the time.

Wind speed was “no more than eight knots (9mph)” at 03:00 – about an hour before the incident. Some 55 minutes later it had increased to 30 knots (34.5mph), and it had accelerated to 70 knots (80.6mph) by 04:06 when the yacht capsized.

As the storm intensified, several crew members were working in response to the conditions. The deck hand went onto the deck to close the yacht’s windows.

Five people were injured “either by falling or from things falling on them” and the deck hand was “thrown into the sea”, the report says.

Two of the yacht’s guests used furniture drawers “as an improvised ladder” to escape their cabin, it adds.

Dr Simon Boxall, Oceanographer at the University of Southampton, said the Bayesian was in “the wrong place at the wrong time”.

“The priorities for the crew would have been to shut the hatches and the doors, which they did,” he told the BBC.

This means speculation about water flooding in because everything was open is “obviously not the case”.

“The next priority would have been to start the engines – so they would have some manoeuvrability to position themselves within a storm – and to then lift anchor, which the crew did, but this takes time,” he added.

“It’s not like a car where you jump in and turn the key. It would take 5 or 10 minutes before you can start the engines with a vessel of this size.”

Survivors escaped on the Bayesian’s life raft and were rescued by a small boat dispatched from another nearby yacht, the report says.

Mike Lynch was a prominent figure in the UK tech industry, where his backing of successful companies led to him being dubbed the British equivalent of Microsoft founder Bill Gates.

But the latter years of his life were consumed by a long-running legal dispute which resulted in him being controversially extradited to the US.

Inquest proceedings in the UK are looking at the deaths of Mr Lynch and his daughter, as well as Morgan Stanley International bank chairman Jonathan Bloomer and his wife, Judy Bloomer, who were all British nationals.

US lawyer Chris Morvillo and his wife Neda Morvillo also died in the sinking, along with Canadian-Antiguan national Recaldo Thomas, who was working as the yacht’s chef.

Fifteen people managed to escape on a lifeboat, including Mr Lynch’s wife, Angela Bacares.