HMS Colossus: debris field survey 2004
Although the main aim of the survey was to ground-truth the anomalies identified in the magnetometer survey conducted by the ADU in 2002, a number of other dives were also undertaken. These included two dives on the main stern section of wreckage. The first of these was to make an underwater video record of the wreck. Unfortunately, however, most of the site was obscured by loose kelp during this dive. The second visit was to obtain samples of the copper alloy sheathing and fastening bolts for analysis (agreed with EH beforehand). Accordingly, samples were obtained of sheathing, a copper fastening bolt and a bolt-washer. Tim Allsop reported an area of surviving timber to the south of the stern site (position 260085E 5535373N5), but a search of this area revealed no visible timber.
Of the 42 anomalies identified, 26 were investigated during the 2004 debris field survey. The area searched varied according to the type of seabed encountered. It was usually possible to search a circle of radius 25m on flat sand (an area of just under 2000 m2) whereas in thick kelp it was rarely possible to search more than a 10m radius circle (just over 300 m2). Of the 26 anomalies investigated, 16 resulted in the identification of significant iron objects, which were recorded and surveyed. The remaining 10 searches did not locate anything likely to have caused the magnetic anomaly. In these cases, either the object was buried beneath the seabed or the anomaly was not caused by a seabed artefact.
It was not possible to investigate all the identified anomalies, mainly due to five days which were lost because of bad weather. We intend to investigate the remaining 16 anomalies during the 2005 debris field survey.
5 NB All positions in this report are given in UTM zone 30 using the WGS84 datum