Crucial questions have emerged about what caused the Bayesian superyacht to sink so rapidly, as five bodies were brought up from the deep, including that of tech billionaire Mike Lynch.

Vision that emerged on Wednesday (AEST) showed the $58-million luxury vessel owned by Lynch sinking off Sicily in less than a minute after it was hit by a freak waterspout.

However, a nearby boat, the Sir Robert Baden Powell, was largely spared in the wild storm and managed to rescue the survivors.

Investigators are now asking if it was merely that the waterspout knocked the Bayesian to its side, allowing water to pour in through open hatches – or were there other contributing factors from the yacht itself that exacerbated the tragedy?

Among the questions are the position of the keel. On a large sailboat such as the Bayesian, it might have been retractable, to allow it to enter shallower ports.

“There’s a lot of uncertainty as to whether it had a lifting keel and whether it might have been up,” Jean-Baptiste Souppez, a fellow of the Royal Institute of Naval Architects said.

“If it had, then that would reduce the amount of stability that the vessel had, and therefore make it easier for it to roll over on its side.”

Karsten Borner, the captain of the Sir Robert Baden Powell, said his craft had sustained minimal damage – just a broken frame awning. That’s despite winds he estimated reached 12 on the Beaufort scale, which is the highest, hurricane-strength force.

Borner said he had remained anchored with his engines running to try to maintain his boat’s position as the storm, which was forecast, rolled in.

“Another possibility is to heave anchor before the storm and to run downwind at open sea,” he said in a text message.

But he said that might not have been a viable option for the Bayesian, given its trademark 75-metre-tall mast.

“If there was a stability problem, caused by the extremely tall mast, it would not have been better at open sea,” he said.

Yachts like the Bayesian must have watertight, sub-compartments that are specifically designed to prevent a rapid, catastrophic sinking, even when some parts fill with water.

“For the vessel to sink, especially this fast, you are really looking at taking water on board very quickly, but also in a number of locations along the length of the vessel, which again indicates that it might have been rolled over on its side,” Souppez said.

Bodies brought up

Divers in Italy have recovered the bodies of five missing passengers from the deep while the search continues for the last one.

Rescue crews unloaded three body bags from rescue vessels that pulled into port at Porticello.

Salvatore Cocina, head of the Sicily civil protection agency, said two more bodies had also been found in the wreckage for a total of five.

The operation to search the hull on the seabed 50 metres underwater had quickly turned into a recovery, not a rescue, given the amount of time that had passed, maritime experts said.

The Bayesian, a 56-metre British-flagged yacht, went down in a storm early on Monday (local time) as it was moored about a kilometre off the Italian island.

Civil protection officials said they believed the ship was struck by a tornado over the water, known as a waterspout, and sank quickly.

Fifteen people escaped in a lifeboat and were rescued by those aboard the Sir Robert Baden Powell. One body – that of the ship’s chef, Recaldo Thomas, of Antigua – was recovered on Monday.

Thomas was born in Canada, according to his cousin David Isaac, but visited his parents’ homeland of Antigua as a child. He moved permanently to the tiny eastern Caribbean island in his early 20s.

Italian officials previously listed Antigua as the nationality of someone on board.

The fate of six missing passengers has driven the search effort. They include Lynch, his 18-year-old daughter and associates who had successfully defended him in a recent US federal fraud trial.

Italian coast guard and fire rescue divers continued the underwater search in dangerous conditions.

Because of the wreck’s depth, special precautions are required. That includes divers working in tag teams and spending just 12 minutes at a time searching.

-with AAP