Site stabilisation on HMS Colossus

English Heritage MRTM summaries. 2002/2003

EH Project Number:	3593MAIN
Funded Unit:	Darkwright

Four separate operations were undertaken on Colossus this year. These were the stabilisation trial, replacement of primary control points, survey work at the stern of the wreck and a series of escorted site visits.

Stabilisation trial

This work was commissioned by English Heritage. The intention of the stabilisation trial is to ascertain whether it is possible to protect the timber which is currently exposed and to prevent the buried timber from becoming exposed. The aim of the trial is to establish the efficacy and economic viability of three different protection strategies in the conditions prevailing on this site. By recording the prevailing conditions on the site it is hoped that a link can be made between the protection methods and the environmental conditions prevailing.

The geotextile mats, timber samples and sub-sea datalogger were deployed in May 2003. Sand level monitoring points were also established around the wreck to monitor sediment levels. In August and October timber sample blocks were retrieved and analysed by Mark Jones of Mary Rose Archaeological Services. Data was successfully recovered from the datalogger, which has now been removed from the seabed for the winter. The datalogger will be redeployed in April-May 2004. The trial is scheduled to end in May 2005, the final report will be submitted by July 2005.

Replacement of primary control points

The primary control points were installed in 2001 and 2002. They consist of 10mm diameter steel reinforcing rod driven into the seabed. Some galvanised steel nails were also used, fixed into the timber of the wreck. While trilaterating the trial areas and the sand monitoring pins it became apparent that considerable corrosion of these control points has taken place. The diameter of the reinforcing rods had been considerably reduced, particularly at the junction with the seabed where some had been reduced to 2 or 3mm in diameter. Similarly, the galvanised nails had almost rusted through. The effect was similar to that previously noticed on the upstanding copper fastening pins of the wreck.

Survey

This work was also commissioned by English Heritage. The stern of the vessel continues to be exposed by erosion of sediment from the site. Timber at the stern of the vessel is now standing 0.25m proud of the seabed. These timbers were thought unlikely to survive the coming winter storms so a detailed survey of this area was undertaken. The area surveyed comprises 108 square meters, bounded by contol points. The survey was accomplished in six days of diving.

Escorted Visits

About 40 divers were escorted around the site on 11th and 12th of August 2003. About half of these were visiting divers, the other half were local Scilly divers. The divers were escorted by members of the regular dive team in groups of four or five.

This page was published on 09/02/2004