WreckMap Portland

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Thursday, April 3, 2003

WreckMap Portland 2003
The NAS Training WreckMap Portland 2003 project took place in and around Portland Harbour, Dorset between the 19th and 23rd of May 2003. The project evolved through consultation and collaboration between NAS Training, the Dorset Coast Forum and the Weymouth Museum, with the aim of involving recreational scuba divers in the recording of wreck sites of historic interest in Weymouth and Portland.

Weymouth and Portland were chosen for the NAS WreckMap project for several reasons, the primary reasons being the existence of a maritime SMR held and maintained by Dorset County Council and the proactive marine life recording undertaken by the Dorset Wildlife Trust. This maritime SMR database currently consists of 1473 records of wrecks, 91 records of structures, 47 records of single finds and 137 records of strandings.

The project aimed to contribute to this database by providing current information on the condition of existing entries and by highlighting new sites not present on the database.

For more information on the 2003 project please click here.

WreckMap Portland 2004
The NAS Training WreckMap Portland 2004 project took place in and around Portland Harbour, Dorset between 17th and 21st May 2004.

The first WreckMap Portland Project took place in 2003 and evolved through consultation and collaboration between NAS Training, the Dorset Coast Forum and the Weymouth Museum, with the aim of involving recreational scuba divers in the recording of wreck sites of historic interest in Weymouth and Portland. The 2004 project aimed to continue the work from WreckMap Portland 2003.

As in the 2003 project, Weymouth and Portland were chosen for the NAS WreckMap project for several reasons. The primary reason being the existence of a maritime SMR held and maintained by Dorset County Council and the proactive marine life recording undertaken by the Dorset Wildlife Trust. This maritime SMR database currently consists of 1473 records of wrecks, 91 records of structures, 47 records of single finds and 137 records of strandings.

The project aimed to contribute to this database by providing current information on the condition of existing entries and by highlighting new sites not present on the database.

For more information on the 2004 project please click here.

State of the Art Mapping of Portland Harbour - August 2004
In 2003 and 2004, as part of the "Diving with a Purpose" initiative the Nautical Archaeology Society mapped some of the wrecks in and around Portland Harbour in Dorset. In 2004, the state of the art mapping project provided some of the most comprehensive images of the wrecks to date, highlighting their condition, the impact they have on the seabed and even discovering some features that archaeologists are getting very excited about.

As part of the 2003 Wreckmap Portland Project we were able to undertake a side scan survey of several wrecks including HMS Hood, the Countess of Erne and the M2 submarine. The side scan sonar produces and receives acoustic pulses of sound with the sensors normally being towed astern of the survey vessel on an armoured cable. By "flying" close to the seabed the transducer mounted on the towfish can produce an acoustic shadow behind objects standing proud of the seafloor. Whilst the sidescan sonar can present a clear image of the overall nature of a target and its surrounding environment, the image is often distorted and contains little information about the true 3-D shape of the object. This was particularly true of HMS Hood, which was difficult to survey due to its location between the breakwaters at the southern entrance to Portland Harbour.

To overcome these problems it had always been the hope to try and use the latest marine geophysical tools on the wrecks at Portland and finally, in August 2004 after months of sweet-talking, the NAS managed to undertake a multibeam sonar survey. Modern high-resolution multibeam sonar offers an opportunity to cover a relatively large area from a safe distance above the target, while resolving the true three-dimensional (3-D) shape of the object with centimetre-level resolution.

The survey used the first of a new generation of dynamically focused multibeam sonars, a Reson 8125. This system sends out 240 beams distributed over a 120° swath every second. The near-field beam-forming capability of the Reson 8125 combined with 3-D visualization techniques provided an unprecedented level of detail. The 8125 was deployed on a custom-built pole mounted onto the starboard side of the MV Divetime, and local charter boat shipper, Paul Pike expertly steered the boat over the wrecks. This enabled the sonar to scan the seabed as easily as if painting a wall with a roller.

To interpret the scans, colour is used to indicate the depth. White represents the shallowest depth through to pink, yellow, green and then blue for the deeper areas. The scale of the colours can be adjusted for each plot to suit the relative depths. By using additional software the images can then be viewed from different angles and perspective as though actually diving the wrecks. The black sections represent those areas outside of the scan's path together with any structures that reach above the water level. The harbour wall, for instance, will be shown as black.

Please click here for a summary of the findings. The full results of the survey were presented at the November 2004 NAS Annual Conference that took place in Portsmouth.

International: 
No
Area: 
England