The crew of the doomed Bayesian superyacht were 'unaware' of its 'vulnerabilities' to extreme winds which caused it to 'violently' knock over and sink, British investigators have said.

The 184ft vessel capsized off the coast of Sicily last August killing seven including its British billionaire owner Mike Lynch and his 18-year-old daughter Hannah.

The Marine Accident Investigation Branch (MAIB) said the £30million yacht was fatally compromised when 80.6mph winds struck its beam, causing it to heel violently to a 90-degree angle.

Preliminary investigations shows that wind speeds of 63.4 knots (73mph) directly on the vessel's beam would 'likely result in the vessel capsizing'.

The interim report that 'vulnerabilities' were 'unknown to either the owner or the crew of Bayesian' as they were not included in the stability information book carried on board.

Andrew Moll, Chief Inspector of Marine Accidents, said: 'The findings indicate that the extreme wind experienced by Bayesian was sufficient to knock the yacht over.

'Further, once the yacht had heeled beyond an angle of 70 degree the situation was irrecoverable.'

Giovanni Costantino, CEO of the Bayesian's builders The Italian Sea Group, has previously said the sinking was 'down to human error' and insisted that it was 'unsinkable'.

The detailed report provides an agonising breakdown of events, charting for the first time how the tragedy unfolded minute by minute off the coast near Porticello.

The MAIB have said however that this is an interim report based on limited verified evidence. 

On the night of August 18, the Bayesian had anchored next to the Sir Robert Baden Powell -a boat which would later rescue survivors – to shelter from the forecast thunderstorm.

At 3am, the deckhand on duty noted the wind as being at 8kts (9.2pmh) but thought that the thunderclouds and lightning seemed to be getting closer.

Less than an hour later at 3.55am, the deckhand 'videoed the advancing storm and posted it to their social media feed' before closing hatches and cockpit windows.

Within minutes the winds had picked up to 30kts (35mph) and the Bayesian was listing and dragging its anchor.

At around 4am, the deckhand woke up the skipper and the crew leapt into action by starting the generators and preparing to manoeuvre the Bayesian.

Meanwhile a British mother and her partner woke up and took their one-year-old daughter to the boat's saloon.

The chef Recaldo Thomas, who would die in the tragedy, was in the galley securing the cutlery, pots and pans and called 'Good morning!' to the nearby stewards.

But as disaster struck as the skipper prepared to manoeuvre, the wind suddenly increased to more than 70kts (80.5mph) ripping the awning away.

At 4.06am the Bayesian 'violently heeled over' in less than 15 seconds to a 90-degree angle.

This sent people as well as furniture flying across the deck leaving five people including the captain were injured while a deckhand was thrown into the sea.

Two guests trapped in their cabin were forced to used furniture drawers as an improvised ladder to escape into the saloon area.

The report said there was no indication of flooding inside the vessel until water came in over the starboard rails and, within seconds, entered the cabins down the stairwells.

The yacht's crew were able to push four guests through the cascading water up to the skipper on the flying bridge.

The Chief Officer who had been swept to the back of the saloon and into another air pocket, dived down to open the sliding doors at the end of the saloon and managed to swim clear of the vessel.

The captain called for the guests and crew who managed to escape to swim clear of the mast and boom as the vessel sank.

In the water, a deckhand improvised a tourniquet for a one of the guest's gashed arms, while a baby was kept afloat on a cushion.

In the darkness, some of survivors were treading water while others held on to some cushions that had floated free from the yacht.

One of the guests frantically searched for other survivors in vain using the torch from their phone while the captain and chief officer frantically freed the life raft from the sinking wreck.

At around 4.24am the liferaft was inflated and the survivors were able to get inside it where the crew began administering first aid.

Desperate to raise the alarm with the nearby Sir Robert Baden Powell, the chief engineer fired several flares before they were spotted at 4.43am.

The skipper of Sir Robert Baden Powell dispatched its tender towards the 15 survivors and despite searching the area no one else was found.

The bodies were subsequently recovered after an agonising five-day search of the wreck on the seabed.

Morgan Stanley International bank chairman Jonathan Bloomer, 70, and his wife, Judy Bloomer, 71, US lawyer Chris Morvillo and his wife Neda Morvillo were among the dead.

The MAIB said its ongoing investigation is based on 'a limited amount of verified evidence' as a criminal investigation by Italian authorities has restricted access to the wreck and other evidence.

A project to recover the Bayesian is set to resume on Thursday after a diver died during underwater work.