Left: SW90 Allsmoke was a custom build that pushed Southern Wind to a higher level. Above: the carbon sub- floo frames are fabricated in house
maestro Stefan Falcon, has developed and gradually refined an exclusive technique for epoxy infusion to produce a laminate with far better technical properties than any other infusion method. Some of the details are trade secrets, but in essence it’s a three-shot process where the outer skin of the hull is vacuum-infused into a female mould and fully cured, then the core is bonded to it with structural epoxy adhesive (which is lighter than infusion resin). Finally, after the core bond is cured, the hull’s inner skin is infused on top. Foam core for infusion is usually
supplied as sheets with pre-cut slits, which make it easier to bend the material around the contours of a hull and also help to distribute the resin during the infusion process. ‘However, this adds hundreds of grams per square metre of extra resin,’ Falcon says, ‘and in the long term the grooves can increase the risk of print through when the hull is exposed to sunlight. To avoid these issues we have developed a technique that uses plain foam sheets instead of the typical cut ones. The foam sheets are individually cut to shape and pre-bent to exactlymatch the inner surface of the hull.’ Andrea Micheli, Southern Wind CCO,
explains that the shipyard’s vacuum- infused laminate has produced results that are close, in terms of quality and performance, to the high-end prepregs used in carbon spars and grand prix raceboat hulls, which need to be stored in a freezer and cured in an autoclave.
Micheli’s figures indicate that the
‘Hull construction is a three-shot infusion process’
resin-to-fabric ratio of prepreg laminate in a raceboat hull is typically 33-34 per cent; SouthernWind’s infusion technique delivers a ratio of 36-37 per cent at amuch lower cost. These figures are far better than it’s possible to achieve with normal one- shot infusion, which also carries amuch greater risk of dry spots in the laminate. Quite sensibly for a
shipyard whose ocean- going yachts are designed and built to last a lifetime,
SouthernWind will only use foamcores rather than Nomex honeycomb between the outer and inner skins of its hulls. The weight saving of Nomexmakes sense for boats that are stored ashore between races and tend to have a short competitive life. But the higher risk of delamination – which is inherent, because honeycomb has a far smaller surface area that can bond with the laminate than a sheet of foam– is unacceptable for a cruising yacht that spendsmuch of its life bumping
against docks, quays and tenders, and then has to stand up to the stresses and shock loads of hard ocean sailing. There are applications where the combination of honeycomb core and prepreg laminate deliver a big weight saving benefit without any compromise in durability, such as bulkheads and decks, anchor lockers and lazarettes. The risk of delamination here is much lower and honeycomb core is exceptionally strong in compression, so for highly customised builds like the Reichel/Pugh designs Allsmoke and Morgana, and the Farr Yacht designs Sorceress and Taniwha, where performance is a higher priority than sound insulation, Southern Wind offers Nomex and prepreg carbon. And where ultimate strength is required in a solid laminate – rudder stock tubes, for example – autoclave-cured prepreg carbon is always used. The three-part female hullmoulds that
are now widely used in large composite yacht construction were originally another SouthernWind innovation. Themould is
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