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Ship superstructures are commonly manufactured from steel but composite sandwich structures could be an alternative leading to significant weight savings. In addition to these weight savings using sustainable materials could reduce the environmental impact of ship production, operation and recyclability in shipping. However, these materials must be capable of equal performance to those that are currently used. Comparing sandwich panels is complex as there are many objectives, stress to strength ratio, sustainability, cost and mass, and variables such as the skin and core materials and thicknesses. Due to this complexity Genetic Algorithms are used to compare potential designs, providing different material selections for different combinations of objectives. The comparison between different Genetic Algorithms demonstrates that HEIA is the most effective algorithm but with all of the algorithms having equivalent performance on these problems. The optimisation provides a set of 716 feasible designs, with balsa being the most popular core but with feasible solutions split between the flax, carbon and glass skins.

Flax fibres are often documented as having equivalent properties to E-glass ones. Based on these comparisons they have been proposed as a suitable replacement for E-glass in structural applications. However, some recent experimental studies demonstrate that flax behaves differently to conventional composites at the structural scale, which indicates that the capabilities of flax need to be better understood at this scale. This paper therefore uses reliability analysis to generate flax structures with an equivalent safety to those in E-glass, accounting for the change in behaviour. An extensive literature review of flax laminate mechanical properties is performed to define their range and variations. These values are used to simulate probabilities of failure which demonstrate that flax structure needs to be 2.4 times heavier than the E-glass structures to have an equivalent safety. It concludes that flax fibres might be used in some applications but cannot replace E-glass in volume constrained structures.

Natural fibres exhibit improved sustainability and similar mechanical properties to E-glass. However, for laminates there is a larger difference in properties and limited assessments of structural components. An analytical method for grillages is developed which is generally shown to predict the stress to within 5% of an FEA model. The simulations demonstrate a change in structural response between flax and carbon, with flax demonstrating higher stresses than expected for the lower Young’s modulus for the same topology. Flax is shown to be more sensitive to transverse Young’s modulus than standard composites and a better characterisation of this property is required.

Due to environmental challenges it is important to investigate potentially more sustainable new materials, including natural fibre reinforced composites. Whilst a number of natural reinforcements show promise there is a concern that laminate properties are too difficult to predict due to the lack of uniformity in natural fibres. The paper quantitatively evaluates the high variability observed at yarn scale, at cloth scale, which shows significant decreases, and at laminate scale, showing comparable variability to synthetic based composites. This demonstrates that natural fibre reinforced composites have reproducible properties at the macroscale level and provides a pathway to application in industry.