more than peripherals like hatch covers and internal parts will have a negative impact on performance. The fact that Crosscall came out
of GLC’s shed weighing less than its design displacement is remarkable, given that flax can easily absorb a lot more resin than glassfibre does unless the infusion process is carefully and skillfully controlled. ‘If we compare the materials flax is twice as light as glass but only half as strong,’ Gosselin says. With the right infusion technique a flax fibre hull can be the same weight as a glassfibre hull and very nearly as stiff, he explains, but its lower strength limits its use in an ocean racing hull that needs to be fully optimised for light weight and high performance. ‘For a non-racing boat with lower performance flax is OK,’ he says. 'But it’s more expensive today and the cost can be a big problem.’ At this early stage of its adoption, flax is also more time- consuming for boatbuilders because, like any new material, they don’t have the familiarity and long experience of using it. Crosscall’s construction is exactly
the same as any comparable boat built in all glassfibre, Gosselin says. Epoxy resin is used throughout as it’s stronger and lighter than polyester or vinylester, and all parts are made with a high-density closed cell PVC foam core. Four different types of glassfibre are used as well as the flax fibre. All of the fibres and foam, as well as the resins, are Sicomin products. The hull was moulded and infused
in one piece and the deck – including the cockpit – was also infused as a single part. The internal structure was then laminated into the hull by hand before the hull and deck were finally bonded together. Epoxy bonding primer makes demoulding easier and also serves as an
Above and right: a hybrid biaxial fibre with a 50 per cent flax content was created for Crosscall’s cockpit, ballast tanks and other non-structural parts. Internal structures are laminated into the hull with Sicomin SR 8200 before the hull and deck are bonded with Sicomin’s Isobond SR 7100 which has a very high fatigue strength and excellent resistance against micro crack propagation
undercoat in the polyurethane exterior paint system, which is used instead of gelcoat to protect the epoxy hull from UV damage. The main infusion resin selected
for Crosscall’s construction is Sicomin’s SR 1710. This is a high- modulus structural epoxy system with extremely high performance. Designed specifically for infusion and injection, it has very low viscosity and its low-reactivity hardener makes it suitable for large part manufacturing. SR 1710 has excellent mechanical properties, especially its inter-laminar sheer strength and it retains those properties in a wet environment, so it’s ideal for the hull of a high- performance ocean racing yacht. Sicomin’s SR 8200 was used to
laminate the internal structures to the skin of the hull. Ideal for hand laminating, this system includes a choice of hardeners with a wide range of reactivity, which makes it equally suitable for making large or small parts. Its three main advantages for boatbuilding are low toxicity, extremely strong mechanical properties and relatively low cost. ‘During application the low level of odour and fumes is remarkable,’ says Tom Kerriou, Sicomin’s project manager for the Crosscall build. ‘Because the maximum temperature resistance is at least 90°C, the parts need to be post cured to enable them to work at a service temperature of 60 to 70°C.’ The hull and deck are joined
together with Sicomin’s Isobond SR 7100. This high-performance adhesive epoxy is specifically designed for composite structural
bonding and – crucially for the hull of an ocean racing yacht – it has very high fatigue strength and excellent resistance against the propagation of micro cracks. Thanks to its gel texture it is easy to apply even on vertical surfaces and three variable speed hardeners are available. Another product that played a very
useful role in this build is the epoxy bonding primer, Undercoat EP 215 HB+ supplied by Sicomin’s sister company, Map Yachting. ‘We have been using it for six years and we don’t make any parts without it,’ Gosselin says. ‘It is a good interface between the composite part and the hull paint, it’s easier to demould, it gives a surface with low porosity and it’s very easy to sand, much easier than resin.’ It’s normally used as a very thin film but a thicker coat can be applied if there is more porosity on the surface. Since the launch of Crosscall GLC
has started building a second Lift V2 Class40 and a third one is planned. ‘The hull and deck will be exactly the same but we are making some modifications to the internal structures,’ Gosselin says. ‘We have moved the mast step aft by 10cm and the keel is slightly modified.’ The weight distribution will be subtly changed to account for the Lift V2’s higher-than-expected boatspeed, with more weight carried further aft to keep the bow trimmed up when power reaching in big waves. ‘The second boat is all glassfibre
because the sailor didn’t want the complication and expense of flax,’ Gosselin says. ‘But for the next one we’re talking about flax again.’
www.sicomin.com
❑ SEAHORSE 65
GLC COMPOSITES
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