If this Finnish builder of luxury yachts is any indication, composites made with natural fibers are inching closer to mainstream boatbuilding applications. Later this year, Baltic Yachts, operating 280 miles (450.6 km) south of the Arctic Circle, will launch its Baltic 68 Café Racer, a 68‘ LOA (20.73m) daysailer with a fresh approach to composite construction: A large portion of the hull material incorporates renewable fibers such as flax as reinforcements in an effort to reduce the boat’s carbon footprint. Flax’s excellent sound-deadening properties, Baltic says, also help reduce the use of insulation, thus saving space and weight. Other interesting details include an electric propulsion system and, quite possibly, a microturbine, not a diesel generator, to charge the electric-drive batteries while under way to extend the vessel’s motoring range.
While Baltic serves a high-end market with customized luxury sailing yachts, the adoption of renewable fibers in composite materials is not just a gimmick for a wealthy client. The Finns’ methodical approach could herald a switch for the leisure boatbuilding industry to incorporate more sustainable construction materials whose desirable properties like stiffness and lightness compare favorably to those of conventional fiberglass or carbon fiber but are easier to reuse and recycle. Renewability aside, flax also has an appealing look and feel and can be dyed and pigmented, offering interior designers near limitless color variations.
Even though Baltic does not yet build entire hulls from flax like Green Boats in Germany does (see “The Quest for Cleaner Composites,” Professional BoatBuilder No. 188), it has used this natural fiber for interior panels and floorboards on the Baltic 130 (LOA 43m) My Song, launched in 2016. “The last two years we have been actively testing, and are using flax for nonstructural parts in the Baltic 146 Custom,” said Baltic spokeswoman Elisabet Holm. “We have now taken it even a step further, and flax makes up more than 50% of the Baltic 68 Café Racer’s hull reinforcement.”
Baltic Cafe Racer Uses Prepregs and Different Cores
Unlike the way Green Boats in Germany infuses parts, Baltic used special prepregs over different core materials, depending on loads and the corresponding strength requirements. Baltic’s composite materials purchasing manager, Thomas Lill, said the yard chose Gurit’s Sprint ST94 and ST95 systems, also suitable for E-glass, which come in biaxial, twills, and unidirectional weaves, with low to no crimp and twist and optimized for lightweight reinforcement. “Different fibers require a different amount of resin to become saturated,” Lill said about the mixed-fiber layup. “This isn’t a problem as long as you have a carefully calculated and correct resin amount in each and every one of the layers. Then none of the layers have a need to cannibalize resin from the other.”
For cores, Gurit Corecell was employed for the hull topsides and slamming areas, Baltek balsa in the aft hull bottom and bulkheads, and Armacell recycled PET foam for nonstructural interior panels. Cork, too, is part of the material mix, mainly to dampen sound and vibrations. How will all this help turn the Café Racer into valuable recyclate at the end of its useful life? “Balsa and cork could be used for energy production, releasing very few toxic gases during the process, since both are wood,” Lill explained. “The PET foam can be collected and recycled into new foam, for example.”
Once the yard figured out the properties and the behavior of flax-based composite materials, it had to decide whether the best application was to completely replace carbon fiber or to combine the two laminates. “Flax fiber is lighter than carbon but not as strong. It also needs more resin to fully wet out, and therefore the final weight is not always lighter,” Holm said. About specific structural/nonstructural applications in the Baltic 68 Café Racer project, she said, “The hull outer-skin laminate is a mix of flax and carbon fibers. In the solid-laminate bottom area of the hull [midships bottom], flax is used to bulk up the thickness. The 11 structural bulkheads are all using flax skins too and a balsa core. Regarding nonstructural applications, we are using flax mainly for interior parts, like floorboards.”
Baltic is not ditching all other composites in favor of flax fibers, but it is making judicious calls on where to use each type of fiber depending on the loads and stresses the laminate must withstand. The company published a video showing how the BComp ampliTex and Sprint material is cut to size and laid over an outer skin of carbon, which, according to the company website, “still provides the best hull surface finish and prevents print-through of the reinforcement laminate.” Once these layers were properly positioned inside the mold, the Corecell core went in, and then the inner hull skin was laid on top. To meet the ambitious hull weight target of 1,557 kg (3,430 lbs), the inner layer is a Gurit Sprint carbon prepreg. “The number of layers varies depending on location [high-load area or not],” Lill explained, “but on average the outer skin [consists of] five layers and the inner skin of three layers. One of the benefits with the Sprint system is that you do not need to debulk nearly as much as with a traditional prepreg.”
With the separate laminates in place, the entire structure is vacuum-bagged to eliminate air pockets and heated to 85°C (185°F) for 16 hours, which causes the resin in the prepreg’s inner layer to evenly and thoroughly saturate the adjacent flax reinforcement.
The first Baltic 68 Café Racer will be launched in spring 2021. Its embrace of sustainability will be further supported by charging the lithium battery bank through hydrogeneration via twin freewheeling propellers or with a microturbine generator, which has yet to be specified. Microturbines are refrigerator-size gas turbines used for power generation. They evolved from turbochargers, aircraft auxiliary power units (APU), or small jet engines.
Asked about the strategic direction Baltic is pursuing with composite materials from renewable fibers, Holm was clear about the company’s goal: “To use more eco-friendly materials in general (fibers, resins, glues, etc.) without losing our identity of being ‘lighter, stiffer, faster.’” Now it also added “greener” to that tagline.
Baltic Yachts Oy Ab Ltd, Alholmintie 78, 68600 Pietarsaari, Finland, tel. + 358 6 781 9200, .
Gurit (USA) Inc., 115 Broadcommon Rd., Bristol, RI 02809 USA, tel. 401–396–5008.
BComp, Passage du Cardinal 1, CH-1700 Fribourg, Switzerland, tel. +41 (0)26 558 84 02.