Finite Element Analysis of Shell-First and Longitudinally Reinforced Frame-Based Wooden Ships

During the period between the 5th century BC and the 6th century AD, two ship construction technologies were prevalent around the Mediterranean Sea: shell-first and frame-based. The shell-first concept was of a strong rigid hull, comprising edge-joined strakes reinforced by transverse frames which were not joined to the keel. In the frame-based technique, transverse frames were connected to the keel to form the skeleton, and the strakes were then nailed to the frames. The hull was strengthened with longitudinal reinforcements. These concepts did not exist in isolation, and at times both techniques were combined. An initial global finite element study (FEA) which analyzed the two technologies, the shell-first Maʻagan Mikhael (400 BC), and the frame-based Dor 2001/1 (6th century AD), revealed that the ships were on a structural par. In that same study, a controlled FEA experiment on generic models was constructed to simulate shell-first and frame-based ships, showing, however, that the shell-first technique exhibited significantly higher structural integrity than the frame-based method. These results prompted a secondary study to explore the mechanical-structural contribution of longitudinal reinforcements to frame-based constructs. Using the same frame-based generic model as in the previous study, longitudinal reinforcements were added in various configurations. The FEA results from this study demonstrated that three critical interdependent factors determined the relative strengths of shell-first and frame-based techniques: the number of transverse frames, the number of longitudinal reinforcements, and their relative locations.