The Bayesian superyacht was “virtually unsinkable”, the chief executive of the firm that built it has claimed.

Prosecutors in the nearby town of Termini Imerese have opened an investigation into the disaster and will seek to establish what caused the boat to sink and whether any of the crew are criminally liable.

They are expected to investigate the keel on Mike Lynch’s superyacht after it was found “partially elevated” – and also whether the yacht’s crew had failed to close access hatches into the vessel before the tornado struck.

Giovanni Costantino, founder and chief executive of The Italian Sea Group, which owns the Perini Navi shipyard that built the superyacht, has defended the boat’s construction and blamed human error for the sinking of the vessel.

He claimed the Bayesian was “one of the safest boats in the world” and was virtually “unsinkable”.

Mr Costantino told Italian newspaper Corriere della Sera: “The passengers reported something absurd, that the storm came unexpectedly, suddenly. That is not true. Everything was predictable.

“Ask yourself – why were none of the Porticello fishermen out that night? A fisherman checks the conditions and a ship doesn’t? The disturbance was completely readable on all the weather maps. It was impossible not to know.

“A Perini vessel survived Hurricane Katrina. You don’t think it could survive a tornado like this?”

Mr Costantino said the strong winds had pushed the boat for four minutes in what he called “drifting”. He claimed the boat then rotated and had begun taking on water before it sank.

While exploring the Bayesian 165ft underwater on the seabed, it was reported divers found that the vessel’s retractable keel was partially raised, raising questions about the boat’s stability at the time of the sinking.

The fin-like structure under the hull helped to stabilise the boat – acting as a counterweight to the mast – and stretched to 9.83 metres when the vessel’s centreboard was fully extended, according to a brochure about the yacht’s performance.

Experts have suggested the keel would normally be fully extended for extra stability during bad weather.

It has also been reported that the space housing the boat’s tender was not fully closed when the ship went down.

From the photos and video images of the ship sinking that have been published, Mr Costantino said it was clear the boat had a blackout which had been caused by a surge of water inside the yacht.

He said there was no doubt the aft hatch had been left open.

“It tilted 90 degrees for only one reason: because the water kept coming in. From the time it started coming in to the time it went down was six minutes. Those who say it disappeared in a few seconds are speaking rubbish.”

Mr Constantino said the crew should have closed all the doors and portholes and gathered all guests on deck in preparation for an emergency evacuation.

James Cutfield, 51, the captain of the yacht was questioned by prosecutors from the Termini Imerese Public Prosecutor’s Office on Tuesday after the vessel sank on Monday morning, Corriere della Sera reported.

Mr Cutfield, originally from North Shore, Auckland, New Zealand, was described as a “well-respected” lifelong seafarer by his brother Mark.

He said Mr Cutfield had captained luxury yachts for the past eight years, worked on them since he was a teenager and was a “very good sailor”.

Mark Cutfield told The New Zealand Herald that his brother was currently recovering in hospital, but that his injuries were not “too dramatic”. He said: “He’s safe, he’s OK.”

A team of four British inspectors from the Marine Accident Investigation Branch (MAIB) also arrived in Porticello to look at the site of the sinking.

The MAIB is looking into what happened because the yacht Bayesian was flying a British flag and is not involved in the search for the remaining missing passenger, it is understood.