Project 6: Diving and Recording Methods
Divers going in for the first dive on the submarine
The hull of the A7 has been modified by a variety of sources; some natural, some during contemporary salvage attempts and some by sports divers in recent years. By investigating how the wreck of the A7 has achieved its current state we may learn more about how similar submarine wreck sites degrade over time and perhaps make better predictions of how they are likely to degrade in the future.
No detailed survey or recording work had been undertaken on this submarine prior to the A7 Project. Very few photographs of her prior to designation have been found during research and no film or video has been located. Some information about the site was made available to the project by sports divers who had visited A7 prior to designation but the quality of that information was questionable. The divers were often not familiar with the features of the submarine, it was usually dark with poor visibility making interpretation difficult and the divers’ ability to remember features on the site will have been adversely affected by nitrogen narcosis.
The three-dimensional model of the submarine created by the multibeam sonar data was used as the starting point for the detailed recording. From the sonar survey we knew that A7 was largely intact, upright, with bows to the west, the periscope was bent backwards and the hull was partially buried in the seabed.
The depth of the wreck made it ideal for using rebreathers. Unfortunately the core archaeology team were not trained in their use and the cost of buying rebreathers and undergoing training was prohibitively expensive. Open circuit scuba was used and it was decided that minimal decompression was to be done for safety reasons so bottom time was limited to just fifteen minutes. Divers using rebreathers did join us for a few dives and they managed considerably longer bottom times, but in most cases were not sufficiently trained to do the recording work. For this small and relatively simple site the use of OC was acceptable but for a bigger or more complex site where more recording time would be required it would be better to use divers trained in the use of rebreathers and detailed wreck recording methods.
Work up dives were completed on shallower wreck sites where the diving procedures could be tested and the recording methods practiced with longer bottom times and less effects of narcosis. A detailed description of the diving method can be found in the Dive Plan.
The condition assessment tasks were started once the wreck had been checked for hazards by the first dive team on site. Visibility on the wreck was limited to a few metres so photography and video were often restricted to small areas of the hull. The seabed around the hull is covered in a very fine, light sediment that was easily disturbed and did not fall out of suspension easily. Even the normal activity of the fish that inhabit the site stirred up enough sediment to adversely affect photography. Daily dive tasks were planned so that any tasks likely to disturb sediment were scheduled to happen after tasks needing good visibility.
The record of the marine life that inhabits the submarine was completed before the site was disturbed by other recording work. Fortunately, the submarine’s steel pressure hull and conning tower were largely free of encrusting marine life so the hull could be recorded without cleaning. This allowed the recording work to be completed as the pink sea fans that were growing on the hull are a protected species and were not to be disturbed.
Photomosaic of the bow of A7 showing the torpedo loading hatches, hole H3 and the remains of the cutwater
When the submarine was first seen in 2014 the conning tower top and periscope were covered in a thick layer of plumose anemones and abandoned trawl net. The net and anemones obscured the details on the conning tower so the net was cut away with shears and the anemones carefully removed using plastic scrapers and a plastic deck brush that would not damage the underlying metal. Removing the net also reduced the weight suspended on top of the conning tower leaving less to be supported by the corroding steel of the conning tower.
The entire hull was recorded on video using GoPro HERO3+ Black Edition cameras and video lights with detailed areas of the boat recorded as required. Before each dive the divers were briefed and provided with a plan of the hull showing the video images that were needed. Video taken on the site was used on subsequent days to help plan the tasks to be completed and to brief the dive teams.
Team diver April Cunningham carrying the Orcalight 2260 canister light
Still photographs were taken using a Nikon D5200 digital camera fitted with an 11mm rectilinear lens in an Ikelite housing and custom dome port. Natural light was used for wide angle photographs on the rare occasions when visibility was good and two Ikelite DS160 strobe lights were used for detail photographs. An Orcalight Seawolf 2260 canister dive light was loaned to the project for evaluation and this was used to provide wide area floodlighting at a distance from the camera. Trials during work-up dives on other wreck sites showed that the 22000 lumen light could be used to produce better results on deep, dark wrecks than could be achieved using the more usual strobe lights. Unfortunately, the times when the Orcalight was available to be taken onto the A7 site the weather was too poor to allow diving or the visibility on site was too low to be able to use the light effectively.
The short time available on site, poor visibility and potential for narcosis meant that survey work on site had to be as simple as possible. Positioning along the hull was controlled by a simple fibreglass tape baseline fixed between two control points so the tape ran along the top of the hull on the port side. The control points were 10mm stainless steel rods that were pushed into the soft seabed with one on the centreline of the submarine just forward of the bow and one on the centreline aft close to the upper rudder bracket. Errors in the measurements along the tape caused by the change in height of the tape along the curved hull were corrected during post-processing. Detailed measurements and sketches were made of particular features on the hull and conning tower and any areas of damage. Some very limited seabed probing was done at the bow to confirm that both torpedo tube doors were closed and at the stern to check if the rudder and hydroplanes were still in place.
Diving operations were run safely with no accidents occurring during the 2 month fieldwork season. Dives were undertaken on the site from 7 August to 29 September 2014. Thirteen divers completed 24 dives with a total of more than 500 minutes on site.