History of Investigations
Almost 200 years after slipping under the waves the wreck was rediscovered in 1981. An expedition lead by Rex Cowan and Richard Larn, involving local divers John Broomhead and Arthur Mack discovered the remains using a magnetometer. The sketch produced by John Broomhead and made available for study by Arthur Mack, appears to show the site as reasonably similar to today in that the mounds of concreted iron ballast are prominent. However, in 1981 there were many more copper pins in position along with more cannon balls covering the ballast mounds.
Sketch plan created by John Broomhead in 1981
During the mid to late 1980's the wreck was rediscovered by the 308 Sub Aqua Association Club who recovered a small number of objects from the site. From the late 1980s it is thought that the site was not dived frequently, although it is listed in Dive Wight and Hampshire publication.
The Impregnable site was the focus of the initial HWTMA Eastern Solent Marine Archaeology Project in 2003 when a site plan was created. Survey in 2003 included monitoring of seabed levels adjacent to the ballast blocks, recording of a feature identified through geophysical survey lying 12 meters to the south of the site, completion of section drawings of the upstanding remains, detailed investigation of the position of individual ballast bars and a timber assessment by dendrochronlogist Nigel Nayling.
Site plan of HMS Impregnable from 2003
Since this time HWTMA has returned to the site to develop understanding of the structure through enhanced survey to gain detail of the ballast bars within the mound and create section drawings. A small number of artefacts have been raised from the site to aid research. Additionally geophysical survey had revealed an anomaly lying 12m to the south of the site, it is thought this may be part of the stern of the vessel.
An HWTMA diver records HMS Impregnable
The levels of seabed deposits around the site have been monitored to assess any changes and their potential impacts on return visits since 2003. The remains are in a seabed which consists of shingle. Trends demonstrate that seabed levels along the north east edge of the site are relatively constant with fluctuations in other areas. Some areas of the site are affected by the actions of burrowing crabs and lobsters which remove sediment from beneath the structure to create their homes. The exposed remains are relatively robust and there appears to be little overall change to the site in the past seven years. In 2010 monitoring was undertaken as part of the Eastern Solent Marine Archaeological Project (SolMAP), supported by the Archaeological Atlas of the 2 Seas project. Further monitoring will continue in 2011.
Diver carrying out monitoring on HMS Impregnable site in 2010