A superyacht owned by tech tycoon Mike Lynch capsized off the coast of Sicily because of design flaws and the captain and crew having no knowledge of its vulnerabilities, British investigators believe.

A preliminary report published on Thursday by the UK’s Marine Accident Investigation Branch (MAIB) runs counter to claims by the builders of the Bayesian that it was “unsinkable” and that the tragedy, in which seven people died, must have been caused by human error.

Investigators said the design weaknesses combined with a freak storm of almost tornado intensity and 70-knot winds to capsize the 184ft-long (56-metre) vessel off the north coast of Sicily on the night of Aug 18 last year.

It was hit by a meteorological phenomenon known as a downburst – a powerful downward column of wind and rain.

The luxury yacht, which was fitted with a 236ft-tall (72 metre) mast, sank in just 16 minutes.

Lynch, who was dubbed “Britain’s Bill Gates”, was among seven people who died, along with his 18-year-old daughter Hannah, who had just secured a place at Oxford University.

The other victims included Recaldo Thomas, the ship’s Antiguan-Canadian chef, Jonathan Bloomer, the Morgan Stanley International bank chairman, and his wife Judy Bloomer. Chris Morvillo, a Clifford Chance lawyer, and his wife Neda Morvillo also died.