A yacht disaster in the Atlantic which prompted a desperate search for its four British crew members was “almost certainly” the result of a damaged keel, investigators have concluded.

Teams examining the capsizing of the Cheeki Rafiki last May admit the absence of survivors and lack of important evidence mean there are still many questions surrounding the “tragic” incident.

But in an official report released today, inspectors say a structural weakness around the keel was the most likely reason for the boat overturning. They also say the event has flagged up a number important safety issues which if addressed could prevent similar accidents in future.

The 39-foot Cheeki Rafiki yacht capsized in the Atlantic several hundred miles off the Canadian coast on its way back to Southampton last year. Her crew of four British sailors, including Steve Warren, 52, and Paul Goslin, 56, from Somerset, were never found, despite two international search efforts by US and Canadian rescue services.

Search teams initially located the upturned hull of a small boat, but poor conditions brought their investigations to a halt. A second attempt, which followed a formal request from the UK Government, led to the discovery of the capsized Cheeki Rafiki, with the sole life raft still on board.

The vessel was not recovered and is assumed to have sunk. But the Marine Accident Investigation Branch (MAIB) have used what evidence is available to piece together an account of what happened.

MAIB chief inspector Steve Clinch said it had been a “challenging” investigation, but the capsizing was “almost certainly as a consequence of its keel becoming detached in adverse weather”.

“Despite two extensive searches, its four crew remain missing and, as the yacht’s hull was not recovered, the causes of this tragic accident will inevitably remain a matter of some speculation,” he said.

“Nevertheless, a thorough investigation has been conducted, that has identified a number of important safety issues, which if addressed, should reduce the likelihood of a similar accident in the future.

“I hope that this report will serve as a reminder to all yacht operators, skippers and crews of the particular dangers associated with conducting ocean passages, and the need for comprehensive planning and preparation before undertaking such ventures.”

The organisation said its inquiry had highlighted several “important” safety concerns, including issues relating to the construction of GRP yachts (glass reinforced plastic) like the Cheeki Rafiki. The vessel is believed to have grounded at least six times since 2007, which the MAIB suggested may have weakened its hull.

“The investigation has identified that in GRP yachts that are constructed by bonding an internal matrix (or lining) of stiffeners into the hull, it is possible for the bonding to fail, thereby weakening the structure,” Mr Clinch explained.

“In some yachts … the design makes it harder to detect when the bonding is starting to fail.

“The report therefore highlights the need for regular inspections of such yachts’ structures … and for the marine industry to agree on the most appropriate means of repair.”

Investigators said they also considered the possibility that the crew’s return passage was a commercial activity.

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