Design, Development, and Manufacturing of a Flax-Fiber Composite Main Foil for the SuMoth Challenge Moth-Class Sailing Dinghy

This paper presents an end-to-end engineering methodology, developed within the SuMoth Challenge framework, for the design, assessment, and manufacturing of a sustainable main foil for the UniCa Sailing Team Moth-class foiling dinghy. The foil was developed using a hybrid flax–carbon composite system with the objective of reducing the environmental footprint of the appendage while preserving the reference outer geometry and CFD-derived load envelope and achieving a structural response comparable in magnitude to that of commercial carbon-fiber foils, such as the Exocet FX1.1. The study integrates (i) reverse-engineered geometric reconstruction of a reference foil based on high-resolution 3D scanning, (ii) three-dimensional CFD analyses to define hydrodynamic load envelopes for subsequent structural assessment, (iii) finite-element-based structural development of hybrid bio-composite laminates informed by experimental characterization of flax reinforcements, and (iv) a full-scale manufacturing process developed for repeatability and internal knowledge transfer within the team. The resulting laminate architecture demonstrates the feasibility of a stiffness-oriented hybrid design approach based on targeted carbon placement and CFD-informed load application. The environmental performance of the main foil was evaluated through an ISO 14044-compliant life-cycle assessment using the MarineShift360 framework within the SuMoth Challenge activities, highlighting substantial reductions in fossil CO2 emissions and non-renewable energy demand relative to conventional solutions. Overall, the study shows that hybrid bio-composites can be effectively employed in high-performance foiling applications and provides a replicable design, manufacturing, and sustainability-assessment pathway for student-led sustainable sailing technologies developed in the context of the SuMoth Challenge. Keywords wind-assisted propulsion; ship design; maritime transport; rigid sails; rotor sails; sumoth challenge; sustainability; foil; moth; flax; composite materials