Methodology Results

In summary, the project has shown that Remotely Operated Vehicles (ROV’s) are effective tools for the archaeological survey of deep wreck sites.
It was possible to define the extent, character, date and also the importance of wreck sites.
Even detailed measurements of objects on the seabed could be achieved with the scaling camera on the ROV. However; just like divers, ROV’s are affected by tidal currents, low visibility and marine growth hiding important features.
While divers might be the better solution for detailed archaeological surveys on shallow wrecks, they are unlikely to provide a cost-effective solution for deep shipwreck surveys.

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When looking at the methodologies for assessing, evaluating and recording wreck sites in deeper water, it was found that the general approach to the ROV survey did not differ very much from the approach taken on the shallow sites. However, a few alterations to the survey plan had to be made:
As the quality of the geophysical background data was fairly low, additional dives were necessary to obtain a general overview of the site and establish the type of site. The use of a digital stills camera and the Tritech ISS scaling camera allowed to take recording from level 2 to level 3 on one site.
Generally, the adverse underwater conditions on site necessitated a high degree of flexibility in the survey procedures.
One of the objectives of this round of the project was to assess the effectiveness of undertaking archaeological recording using ROV and geophysical techniques only. It became apparent that using the geophysical data only, partial level 1 recording was possible. While presence and position of the sites could be established, the available information was not sufficient to determine the type of site.
Applying the methodology outlined before, all deep wreck sites could be recorded to level 2. The use of a scaling camera and a digital stills camera on the ROV allowed partial level 3 recording, even in the low visibility conditions and strong currents experienced on the study sites.
However, it was found that the four main factors limiting survey efficiency that were identified during the shallow water ROV survey in Year One (2005) also affected the deepwater survey. These were:
  • visibility
  • tidal current
  • access, and
  • marine growth
The poor visibility experienced on all of the deep wreck sites made underwater orientation and video recording very difficult. It also limited the use of the underwater stills camera.
Most importantly, the duration of all recording tasks had to be changed as even simple tasks took much longer. Despite this, it proved to be possible to carry out recording, mainly because of the skill and experience of the ROV operator.
The strong tidal currents experienced on all sites limited diving to the slack-water periods and made it difficult to control the ROV. Again the survey efficiency depended mainly on the skill and experience of the ROV operator and on a high degree of flexibility in the survey planning.
The problems of access to enclosed areas on structurally coherent wrecks and dense marine growth preventing the identification and recording of features are indicative for ROV surveys in all environments. These have to be accepted as general limitations.
No environmental issues relating specifically to the location of the sites in deeper water could be identified. The conditions experienced were related to the time of year and the unusual general weather conditions rather than to the location of the sites in deeper water.
When assessing issues related to infrastructure, the choice of support vessel was found to be a critical factor. Using Sara Maatje XV, none of the problems identified during the Year One survey were encountered. The vessel was equipped for establishing three- or four point moorings and the crew was very skilled and experienced. The mooring procedure on each wreck site took an average of 30 minutes and the vessel was generally secured directly above the wreck. Umbilical handling was carried out by the crew and did not pose any additional problems.
>In conclusion, the project has improved the knowledge necessary for specifying and conducting rapid and efficient deepwater ROV wreck surveys in areas with conditions similar to the English Channel.