Possibilities for using environment friendly composite materials as the core hull material for autonomous surface vessels (ASV)
By Mari Valgma, PhD
Small Craft Competence Centre
Introduction to the report
The report gives an overview of the general requirements for an autonomous surface vessel (ASV) and discusses the different material solutions that could be used. One of the key points of interest was to find out if composites based on renewable resources can be used for the ASV hull.
The survey includes background description, what are the expectations for the ASV, what are the environmental conditions in the Baltic Sea and what kind of materials are used in the existing ASVs. The list of requirements for the material selection is given, composite materials and their main differences when compared to aluminium is discussed. Also the possibilities of embedding sensors or solar energy harvesting cells into composites are considered and different resins, fibres and manufacturing methods are introduced, that can potentially be used when manufacturing an ASV.
The survey reveals, that applying bio-materials in ASV production may open new possibilities in bio-composites development, reducing the risks related to boats exploitation and enabling operative fatigue monitoring via smart composite solutions.
Summary of the report
The ASV is planned to travel autonomously for long distances and use mainly renewable energy resources. This plays a key role in dictating the material as the material needs to provide excellent mechanical properties at a minimum weight. This is possibly the main reason why the current long distance ASVs are made of composite materials, and a number of them are made of a high performance carbon reinforced composite.
Aluminium is not really competitive in these applications as it cannot be tailored to suit specific requirements. In composites, different types of fibres can be combined in one laminate to fully optimize the performance of the material. Additionally, it may be possible to insert sensors or solar energy collecting cells into composite laminates.
One of the option is the use already proven conventional composites for the ASV. However, recently have emerged natural fibres and partially bio-based resin systems that are claimed to be comparable with conventional composites. Some of the examples are ampliTex flax fabrics from Bcomp that are compatible with carbon fibres and conventional resin systems, partially bio-based epoxy resins from Entropy Resins, polyester and vinylester resins by Dixie Chemical and Ashland. So far, these new sustainable solutions are claimed to perform as well as the more conventional materials.
Table 4 shows some of the key points to consider when selecting the suitable material.
Natural composites are highly competitive for the use in an ASV.
The performance of composites is affected by the environment. While composites are generally considered to perform well in various harsh environments, there are still some changes in the properties that need to be accounted for in the design phase. While the long-term performance is fairly predictable in conventional composites, it is largely unknown in novel plant-based fibres and matrices. Thorough testing for these materials is required to verify their suitability for maritime applications. For the ASV applications, material performance is freezing conditions and with ice impact also needs to be considered and tested for.
As the material selection for the ASVs tends to go towards high performance composites, then the manufacturing method should be selected accordingly. Possibly the best option is using vacuum infusion processing to achieve good material quality.
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