The Friesland-based skipper who saved 15 people from the luxury yacht which capsized in a storm near Sicily on Monday said he “didn’t think, but did what was necessary”.

Karsten Börner, who was born in Germany but has been living in Lemmer in Friesland for years, happened to have dropped anchor close to the stricken Bayesian, at the port of Porticello, east of Palermo when the storm hit.

“We had been prepared a bit and it started blowing around 4 in the morning. They were hurricane-force winds of 12 Beaufort,” he told local broadcaster Omrop Fryslân.

Some time during the storm a waterspout, or tornado, formed, Börner said. “It was very strong and intense. We had trouble keeping the ship on an even keel, with the anchor in place and the motor running. The yacht was just behind us and we kept an eye on it. At one point it disappeared,” he said.

“One of my guests saw a flare and then I saw another and then me and my helmsman got into the dingy and set out in the direction of the yacht. We found a life raft with 15 people on it, four of them badly injured, and a baby,” Börner told the broadcaster.

After getting the people to his boat and giving them food and dry clothes, the Italian coast guard came to pick up the wounded to take them to hospital. “It was traumatic but at a moment like this you don’t think, you just do what is necessary,” he said.

The yacht, chartered by UK tech entrepreneur Mike Lynch, carried 22 people, six of whom are still unaccounted for, including Lynch, his teenage daughter Hannah Lynch; the Morgan Stanley International chair Jonathan Bloomer and his wife, Judy; and the Clifford Chance lawyer Chris Morvillo and his wife, Neda.

The Bayesian is now on the seabed at a depth of some 50 meters. Divers tried in vain on Tuesday to gain access to the inside of the sunken vessel, where rescue crews believe the six people who are still missing may have been trapped, the Guardian reported.

Lynch had chartered the yacht to celebrate his acquittal in a fraud trial. In a freak coincidence, his co-defendant Stephen Chamberlain was fatally hit by a car around the same time the yach went down.

Theories about what else may have caused the Bayesian to take on water are still being investigated. Waterspouts such as the one that hit the Bayesian, are rare but they happen when the water is too warm.

“The temperature of the water of the Mediterranean is now at 32°, 5° too warm,” Bórner said. His ship was left with only minor damage.