The current paper is intended to provide an overview on the current state of the art for sandwich structures marine applications to support their wider application and identify the key issues to develop. A summary of current rules and standards on marine sandwich constructions is reported. The main critical points concerning design and qualifications are outlined, and some possible developments are suggested, with particular attention to critical loading conditions. An overview of innovative sandwich structures marine applications is included and some comparisons among different structures are provided. Some suggestions on future scenarios for sandwich structures marine applications are yielded.

Weight reduction and materials sustainability are becoming of primary importance for marine structures. A solution to both issues could lie in the application of all-metal sandwich structures. The study suggests the substitution of common marine structures with aluminium honeycomb sandwich structures (AHS), as a green and lightweight alternative, through a new methodology for structure comparison and design. Comparisons were based on bending stiffness equivalence and its relation to other design parameters, used to produce materials charts. A graphical approach based on plots of stiffness requirements, weight reduction goal and failure modes was applied for the identification of the main design variables. The feasibility and effectiveness of the developed approach was illustrated by outlining an example regarding the substitution of a GFRP-based ship balcony overhang with an equivalent AHS. The results showed the possibility to significantly reduce the weight, leave the geometry almost unchanged, and improve the mechanical response.

Green composites have gained increasing attention in recent years as a sustainable alternative to traditional materials used in marine structures. These composites are made from biodegradable and renewable materials, making them environmentally friendly and reducing the subsequent carbon footprint. This review aims to provide a comprehensive overview of green composites materials and their applications in marine structures. This review includes a classification of the potential fibres and matrixes for green composites which are suitable for marine applications. The properties of green composites, such as their strength and Young’s modulus, are analysed and compared with those of traditional composites. An overview concerning current rules and regulations is presented. The applications of green composites in marine structures are reviewed, focusing on both shipbuilding and offshore applications. The main challenges in a wider application of green composites are also highlighted, as well as the benefits and future challenges.

Materials and structures for marine applications are often required to combine high mechanical performance with lightness, but traditional solutions are not always adequate to the scope. The application of biomimetic science could provide innovative and efficient solutions, whose research is the aim of the present paper. In the current work, bamboo samples were subjected to impact both on the outside and on the inside surface. It was found that the impact strength is correlated to the third power of thickness and that the softer inside layers may act as an energy absorbing structure, which enhance impact resistance. Impact tests were also performed on specimens whose outside surface had been abraded and on whole cylindrical sections. The role of graded and hierarchical structure in impact response, suggested some guidelines for bio-inspired structures design. Four bamboo-inspired structures were designed, based on the idea of combining corrugated panels with different geometrical characteristics to resemble bamboo graded and hierarchical structure. These structures were made using 3D printing and tested in compression. The best performance was obtained by the structure which more closely replicates bamboo's hierarchy. Structure performance could be predicted with reasonable accuracy using buckling theory.