The dramatic disintegration of Bernard Stamm’s IMOCA 60 was caused by corrosion, according to the skipper and designer Juan Kouyoumdjian. Matthew Sheahan reports

Since the recovery of Bernard Stamm’s IMOCA 60 Cheminees Poujoulat, which broke in two late last year, a pair of independent specialists has found that the catastrophic failure was caused by corrosion in the alloy honeycomb used in the construction of the hull.

“When we recovered the boat there was a very clear corrosion issue with the core,” Juan Kouyoumdjian, the boat’s designer, explained. “There is no doubt about what caused the failure, but what we don’t yet know is what caused this to happen.

“The investigation is focused on trying to find out how the alloy core corroded so badly. But what we do know is that you need water in touch with the aluminium and a current to create this corrosion.”

He added that where the corrosion was at its worst. the remains of the aluminium core were “like couscous or puree”.

As with most high-performance race boats, the hull construction for a typical IMOCA 60 involves some form of sandwich laminate which,.according to Kouyoumdjian, frequently uses a cardboard or Kevlar-based honeycomb and a foam core in the higher load slamming areas. Cheminees Poujoulat was unusual in that she had an alloy core in some areas of her hull.

“The alloy core does offer some potential advantages,” he continued. “It is cheaper than Kevlar honeycomb and its sheer strength is around 15-20 per cent greater for the same weight. But it also has good impact strength and while it may deform under impact. it is less likely to be destroyed where others will fail completely.”

Nevertheless, he was not comfortable with the use of alloy on this occasion: “I wasn’t in favour of this material in this boat. I would have been happier without it.”
The failure is naturally of serious concern to others in the racing scene who have used this material in the construction of boats. Yet Kouyoumdjian stressed that there were plenty of boats that did incorporate alloy honeycomb in their structures and had been sailing around with no problems.

“The catamaran PlayStation is one example and she is still sailing, but I don’t think it’s an ideal solution for long offshore boats that are sailed short-handed,” he said.
Both Kouyoumdjian and skipper Bernard Stamm agree that the recovery of the broken boat is a big advantage in helping to ascertain what caused the failure.

“It is a miracle that we were able to bring the boat back,” said Stamm. “I had no doubts about reliability before we left Brazil as we carried out a careful study before we left, but in the end it broke. “I think that these boats must be indestructible and must not be able to break,” he continued. “Losing a mast or a keel happens sometimes, but we must not be able to break a hull. The fact that we have recovered the hull will mean that the results of the findings can be used to help others.”

According to Kouyoumdjian those findings will be made public – he is hoping that this will happen within a month.

Could the boat be repaired?
“No,” Stamm said. “Perhaps there is some gear that can be recovered and maybe someone will try to repair her, but  she will never race again.

So, had the failure and the dramatic rescue damaged his confidence? “Only if the failure remains unexplained,” .. he said.