The use of a high-resolution 3D Chirp sub-bottom profiler for the reconstruction of the shallow water archaeological site of the Grace Dieu (1439), River Hamble, UK

The remains of Henry V’s flagship, the Grace Dieu, currently lie buried within the inter-tidal sediments of the River Hamble (S. England). Previous archaeological investigations have been hindered by difficult excavation conditions resulting in a poor understanding of the dimensions, shape and degradation state of the hull’s deeper structure. This study therefore aimed to image, characterize and reconstruct the buried remains of this vessel using a high-resolution 3D acoustic sub-bottom Chirp system with RTK-GPS positioning capability. The accurate navigation and high-resolution data that were acquired enabled the construction of a full 3D image of the site that not only identified the remains of the wooden hull, but also features buried within it. In addition, the degradation state of these buried wooden remains were investigated by calculating reflection coefficients while a hypothetical larger reconstruction of the Grace Dieu’s hull was achieved, through the use of the ShipShape ship design software package. The results of this project demonstrate that (i) acoustic data can be used to successfully image buried wooden shipwrecks, (ii) artefacts are buried within the hull of the Grace Dieu, (iii) there is variation in the degradation state of the buried timbers, as calculated from the acoustic data, with the shell of the vessel being moderately well preserved, and (iv) the Grace Dieu was a very large ship for its time (possibly over 60 m long and 16 m wide). The outcomes of this research not only have considerable implications for the management and monitoring of submerged and buried archaeological sites but also for planning intrusive surveys, should they be required.