The advancement in composite materials allows building primary maritime structures traditionally made of steel, e.g. ship superstructure. Steel and composites can be bonded together using adhesives, forming a hybrid (steel-composite) joint. Despite of the many benefits of composite and hybrid joints, the lack of correct guidelines for approval and design has prevented their uptake by the maritime industry, limiting their usage to secondary structures. This is partly because the long term behavior and failure of hybrid joints is not yet understood. The goal of the EU funded QUALIFY project is to fill this knowledge gap, enabling the development of such guidelines, with the correct objective promote the use of hybrid joints in primary structures in a marine environment.


The advantages of composites stem from their lightweight and manufacturing advantages compared with traditional steel structures.

A composite ship superstructure leads to a:

  • Reduction of the top weight of naval ships (10%), and 1%-7% fuel consumption

  • Similar reduction of harmful emissions 

  • Increase in ship stability

  • Less maintenance required

Hybrid adhesively bonded joints present several advantages with respect bolted and welded joints

  • Significant operational cost saving

  • Low-cost  fast manufacturing

  • Lower tolerance requirements compared with bolting

  • Increased building safety. No hot works and induced welding deformations

  • Can join dissimilar materials such as composite-steel, which is not possible by welding


The project objectives are to enable the certification of hybrid joints for primary structures applications (2022), the widespread use of adhesively bonded hybrid structures in shipbuilding (2022 - 2025), as well as the gradual replacement of metallic parts with hybrid structures in other sectors, e.g. wind turbines (2022 - 2030).

Hybrid Joints

Adhesive (epoxy resin)