Finding HMAS Sydney (II)

Side Scan Sonar Survey

The Sydney wreck site was identified along Line 12, on 6km swath SM-30 side scan sonar data at 1103hrs AWT (0203hrs UTC ) on 16th March 2008.

Sonar data revealed the wreck to be lying upright on the seabed; its hull orientated generally NW/SE with the stern to the north. A large section of the bow lies detached from the main wreck approximately 450m to the NNW.

Key wreck site coordinates are provided in Table 3-1.

A full 6km swath sonar image showing the location of the Sydney wreck site on the starboard sonar channel is provided in Figure 3-1. The red colour of the sonar target is indicative of an acoustically strong, hard contact. Another indicator that this was the wreck site was the anomalous nature of the sonar contact relative to the surrounding seabed, which is featureless and of low acoustic reflectivity.

After finding the wreck site a number of high resolution and reduced swath investigation lines using the SM-30 and AMS-60 sonar systems were run in order to confirm that the sonar target was Sydney. Investigative parameters included target length and width and any salient structural features typical of the cruiser.

Interpreted main wreck length and width values determined from sonar images are 166m and 18m respectively. Dimensions of the interpreted dislodged bow section are approximately 28m long and 14m wide. Acoustic shadowing observed on the sonar images revealed a maximum main wreck height of approximately 14m, and bow section height of 10.5m above the surrounding seabed. These dimensions correlate well to those of Sydney.

Two enlarged high resolution AMS-60, 600m swath sonar images showing the main wreck and dislodged bow section are presented in Figures 3-2 and 3-3 respectively.

ROV Inspection

An ROV inspection of the Sydney wreck site provided visual confirmation of the wreck. High quality still photographic and video imaging confirmed the nature of the sonar targets, including not only the main wreck but also the numerous items of debris and wreckage within the debris field to the NNW.

A summary of the Sydney dive program and approximate water depth at each location is provided in Table 3-2.

ROV inspection Dive 1, Dive 2 and the latter part of Dive 7 concentrated on the main wreck section. Dive 1 was generally unsuccessful as the ROV was unable to exit the TMS garage and was therefore vulnerable to surface vessel movement. This resulted in blurred photographs and the inability of the ROV to approach the wreck safely. This dive was eventually aborted and superseded by Dive 2.

Three Sydney ROV photo location guides from photos acquired during Dive 2 and Dive 7 are presented in Figures 3-4 to 3-6.

ROV inspection Dive 3 and the initial part of Dive 7 were undertaken within the debris field that extends generally NNW from the main wreck. These ROV dives were based primarily on repositioned sonar target data.

A number of large sonar targets were identified within the debris field and although these formed the basis of the respective dive plans, numerous items of both identifiable and unidentifiable debris and wreckage were also observed while the ROV was transiting between them.

The description and position of some of the largest targets identified within the debris field are provided in Table 3-3. An AMS-60, 600m swath sonar image showing the position and description of salient items identified during the ROV inspection of the debris field is provided as Figure 3-7.

Side Scan Sonar Survey

The Kormoran wreck site was identified along Line 9, on 6km swath SM-30 side scan sonar data at 1730hrs AWT (0930hrs UTC ) on 12th March 2008.

Sonar data showed one large section of superstructure lying upright and orientated generally SSW/NNE with the bow to the north, an extensive debris field (debris field #1) approximately 500m to the north east containing another large section of intact superstructure, and a smaller debris field (debris field #2) approximately 1.3km to the north.

Key wreck site coordinates are provided in Table 3-4.

Full 6km and 1.5km swath sonar images of the Kormoran wreck site on the port sonar channel are shown in Figures 3-8 and 3-9. The red colour of the sonar targets is indicative of acoustically strong, hard contacts. As with the Sydney wreck site, this wreck site exhibited anomalous sonar returns relative to the surrounding featureless seabed.

A number of high resolution and reduced swath investigation lines using the SM-30 and AMS-60 sonar systems were run in order to the confirm that this was the Kormoran.

The main section of superstructure to the south is approximately 90m long, 20m wide and up to 20m high, as determined from the sonar images. These dimensions correlated to known dimensions between the midships accommodation and the bow, and were later confirmed by ROV inspection. An enlarged high resolution AMS-60, 600m swath sonar image of the main wreckage is provided as Figure 3-10.

Debris field #1 to the north east is extensive, measuring nearly 1km across and is centred on a large piece of superstructure approximately 50m long, 20m wide and 15m high. An enlarged high resolution AMS-30, 1.5km swath sonar image of debris field #1 is provided as Figure 3-11.

Debris field #2 contains only a few sonar targets, the largest measuring approximately 35m long, 15m wide and 15m. A high resolution AMS-30, 1.5km swath sonar image acquired over debris field #2 is presented as Figure 3-12.

ROV Inspection

An ROV inspection of the Kormoran wreck site provided visual confirmation of the wreck. High quality still photographic and video imaging confirmed the nature of some of the largest sonar targets. Due to time constraints, ROV inspection concentrated on the main wreck section with some time spent investigating the largest items of wreckage identified on the sonar within each of the two debris fields.

A summary of the Kormoran dive program and approximate water depth at each location is provided in Table 3-5.

The wreck of the Kormoran was positively identified during ROV inspection Dive 5. However, the dive was aborted because a jammed manipulator arm prevented the ROV from exiting the TMS garage. Video footage was acquired but no still photographs were taken due to excessive movement of the ROV and TMS unit.

Dive 6 was undertaken in three parts: inspection of the largest section of wreckage followed by an inspection of each of the largest pieces of wreckage within debris fields #1 and #2.

Inspection of the forward section of the wreck confirmed that the vessel had broken near the aft of the main accommodation block. Inspection of the largest item of wreckage within debris field #1 revealed another large section of the superstructure surrounded by numerous items of wreckage. The height of this section was confirmed during the inspection.

Finally, inspection of the smaller debris field #2 to the north revealed the largest item of debris to be a large section of the port midships and included what appeared to be machinery or main engine block, with lettering reading "08KO" found on plating just above the bilge keel. The lettering is consistent with that found on Kormoran ship's drawings.

A Kormoran ROV photo location guide from photos acquired during Dive 6 is presented in Figure 3-13.