A Comparative Structural Analysis of Shell-first and Frame-based Ship Hulls of the 1st Millennium AD

摘要

The 1st millennium AD experienced a significant change in ship construction. A slow transition evolved where ships built 'shell-first' were ultimately supplanted by 'frame-based' ships. Shell-first ships were constructed with strakes edge-jointed using pegged and later unpegged mortise-and-tenons joints, dowels or coaks, and at times, sewing, which resulted in a strong and rigid hull. The strakes were then fitted with transverse frames independent of the keel. Frame-based ships were characterized by transverse frames; most of the frames were fixed to the keel and reinforced by longitudinal components. The hull planks were later fastened to the pre-existing frames. The objective of this study was to examine whether mechanical factors contributed to the transition in ship construction. An initial comparative linear static FEA global comparison analysis was conducted on CAD models reconstructed from two archaeological shipwreck findings: Ma'agan Mikhael (400 BC) and Dor 2001/1 (6th century AD). The Maagan Mikhael shipwreck was representative of the shell-first technique and the Dor 2001/1 shipwreck represented the frame-based technique. The application of standard global stillwater criteria revealed that both ships possessed high degrees of rigidity and low von Mises stress values. Further controlled analyses were performed on two symmetrically identical archetypal quarter hulls while varying load and construction parameters. In all the archetypal load scenarios, the shell-first samples exhibited higher rigidity and less extreme von Mises stress differences than the frame-based samples. Frame-based rigidity and stress levels were directly dependent on the number of frames added to the structure. Further to be researched are the ancillary economic, social and ecological issues intertwined with engineering factors which contributed to the transition.