No longer does the use of bio-resins and fibre in composite manufacturing mean increased production costs because of the need for much more delicate material handling.

Bio-based resins have come a very long way in the last few years. No longer niche products, they are now among the best-selling resin systems on the market. The companies that pioneered these far less toxic and more sustainable, next-generation materials – like Sicomin, the marketleading supplier of liquid epoxy – are now reaping the rewards of their R&D, with massive uptake in major market sectors like automotive, construction and renewable energy, along with some innovative boatbuilders.

A turning point was reached a few years back when Sicomin, a French company with deep roots in highperformance yacht racing, launched a complete range of bio-epoxies whose performance is not just equivalent to the leading petrochemical-based resins on the market, but significantly better – and that’s not merely a manufacturer’s claim, it’s backed up with full DNV GL type approval. Another major milestone was passed this summer when Couach Naval Shipyard became the first to vacuuminfuse a superyacht hull, deck and superstructure in bio-based epoxy. Couach, which builds highperformance military vessels as well as yachts, is renowned for its very high engineering standards.

The 26-metre (86ft), 52-tonne Couach Fly 86/2600 is one of the largest and highest-value structures infused in bio-based epoxy to date, and by far the largest yacht. Sicomin supplied the resin – InfuGreen 810, part of the GreenPoxy range with 38% of its carbon content derived from plant-based sources – and worked closely with Couach to ensure the success of this pioneering application. Sicomin’s GreenPoxy 33 hand laminating bioresins are also used in the Fly 86/2600 for secondary bonding in the yacht’s final assembly.

‘They started with a few square metres on an infusion table and then ramped up to a small-scale hull section of about 20sqm to validate all the parameters, building confidence in the process, the infusion time, what to use in terms of pipe size, pipe distance and reinforcement,’ says Sicomin MD Marc Denjean. ‘You need to clear many small parameters but then when you shoot there is almost no reason for failing. You know it’s going to work, it is a very reliable process.’ The test panels passed quality control and then the entire hull was infused in a single shot.

InfuGreen 810 is ideal for infusing large structures. ‘It’s low viscosity, which is very important for carbon fibre, but not too low – if the resin flows too fast it creates quality defects like porosity,’ Denjean says. ‘Even more important are the wetting properties of the resin itself, and it’s very much better than standard. Mechanical and thermal properties are about the same but with a better flow you get better mechanical properties in the structure. We focus on performance and processability, the bio content is just the cherry on the cake.’ Even so, GreenPoxy has the highest bio content in the market, up to just more than 50 per cent, depending on the product used.

A key innovation in Sicomin’s epoxy infusion process is the use of a transparent primer instead of the usual opaque gelcoat. It’s a gamechanger, Denjean explains, because avoidance of dry spots is even more critical to the strength of a vacuuminfused hull than achieving low porosity. ‘You can see right through the primer and the fibres so it’s easy to identify even the smallest dry spot,’ he says. ‘You can do a complete hull check with 100 per cent certainty.’ Couach is now using the Sicomin clear primer as standard.

The end result from the owner’s point of view is a triple win: a lighter, stiffer and more durable yacht; higher top speed, faster acceleration and longer range; better fuel economy and a smaller eco footprint. A stiffer hull needs less internal structure, which frees up more interior volume, and epoxy is completely immune to osmosis. It does, of course, cost more than polyester but the price of hull materials is a tiny percentage of the overall cost of a yacht – as Denjean points out, the difference is a lot less than the typical value of the wine that’s cellared on board.

Sustainability has given shipyards a customer-driven incentive to upgrade from polyester to epoxy, and Sicomin has invested heavily in lifecycle assessment (LCA), making it easier for a shipyard to manage its own environmental footprint. ‘Until last year nobody asked us for that document,’ Denjean says. ‘But now for some of our customers, like Mer Concept and CDK, providing LCA data for clients is becoming a key part of their build process.’