60ft tris start their engines

The Daily Sail spoke to designers Nigel Irens and Vincent Lauriot Prevost about mast breakages and structural failures

Story from hell

Fred le Peutrec's new Bayer en France has had her own set of problems. During the Course des Phares Bayer pulled out with problems with her aft beam. These were not foil related, but due to the positioning of the headsail sheet winches. These were located on top of the beam and were so loaded up that they were trying to make the beam topple forwards. A mod was prescribed, but when the boatbuilder from MAG attempted the repair he discovered an area of 400mm square where the carbon fibre was not bonded to the Nomex and presumably had been like this since the boat was built.

"It was exactly the same, age old chestnut as they had with the Goss boat [ Team Phillips]," says Irens. Uni-directional carbon fibre is non-porous and so to stick it to the Nomex the builders at MAG had first laid up a layer without U-Ds in it. "Even though the yard had taken great trouble to stick the first skins on which didn't have any uni-directionals in them, to the Nomex, during the cooking of the second half of the skin the temperature got to the stage where the first lot of glue was beginning to go soft and the pressure created in the cells couldn't purge through that surface layer of uni-directional and was enough to push it off locally," continued Irens. So the hot air in each cell expanded lifting off the carbon layer.

If the carbon had not bonded to the Nomex in one spot during construction then it was reasonable to assume that this might be the case elsewhere on the beam. So the team had the beam tested by ultra-sound and so enough the results confirmed their fears, indicating there to be areas throughout the beam where the bonding was good and elsewhere where it was bad.

Irens takes up the story: "So MAG and their insurers teamed up to take the whole aft beam fairing off on the port side with the intention of replacing the core and front skin of the beam. Once they'd got the access to it by stripping the whole of the fairing off - which is a major job - they started peeling the skin back to find there was absolutely no problem anywhere! It was the boat building equivalent of a patient in a hospital being told they've got to have a vasectomy, them doing the operation and then being told "oh, you didn't need it after all.""

Aside from the known problems of laminating carbon to Nomex, Irens says that this episode shows just how hard it is to find out exactly what is going on inside a sandwich laminate by non-destructive testing. "Clearly the ultra sonic equipment did not give the right answer," he says.

Another way they could have tested the laminate is by infra red, where heat is projected at the skin and a thermal imaging camera is put the other side and shows how heat is being conducted through the laminate. Provided that the core is relatively thin the Nomex transmits heat through the laminate where it arrives at the opposite side of the laminate. In theory if the laminate is good, the hexagonal cells of the Nomex should show up as a pattern on the thermal image. However this technique only really works in areas where there is a constant thickness of laminate.

Thankfully Bayer is now back in one piece and has qualified for the Route du Rhum.

Lionel Lemonchois' Gitana X, has been in the yard for the last 10 weeks having her beams reinforced (see below). They too have now added strain guages in the beams to monitor loads. They have also carried out additional work to optimise the sails for singlehanding. The roach on the mainsail for example has been cut down and a staysail has been added.

Continued on page 4...