David Mearns’ Search Diary

Search Diary

by David L Mearns, Search Director

“I consider it one of the great privileges in my life to have led this important project.”

David L Mearns, 12 January 2010  

Monday 14 December 2009 

Search for the Centaur is now underway

Launch of the SM-30 side-scan sonar towfish off the stern of the MPV Seahorse Spirit.

Search for Centaur

The search for the Australian Hospital Ship (AHS) Centaur is now underway. Early this morning at 0750 hours the SM-30 side-scan sonar towfish entered the Northern end of the search box and it is currently being towed at a speed of 2.5 knots along the first 39 kilometre search trackline. The sonar is working well and is producing excellent imagery of the rugged seabed. Unfortunately the seabed is as rocky and mountainous as I had feared, especially in the Northern half of the 1,365 square kilometre search box. The rugged seabed is a major complication that I will be reviewing carefully as the search progresses and I expect I will need to alter my search plans to adapt accordingly.

We are having much better luck with the weather conditions, which are ideal, and the surface currents, which could have been far worse. Fortunately for us a clockwise flowing cold-core eddy current has moved into our location and this has pushed the strong southward flowing East Australian current offshore and away from where we are working. Whereas we should have expected a strong 2-knot current setting us to the south and playing havoc with the ship’s ability to steer perfectly straight tracklines, we currently have a gentle current of 0.5 knots or less. Dr. David Griffin of CSIRO Hobart advises me that these favourable conditions should persist until Wednesday so we intend to make the most of them while they last.

Prior to starting the search we spent all of Sunday conducting sea trials of the two side-scan sonar systems we’ll be using for the search. The SM-30 is a 30 kilohertz (kHz) sonar with an effective search swath of over 5 kilometres and this will be the primary sonar used during the search. The AMS-60 is a 60 kHz sonar that will be used to collect higher resolution imagery of Centaur’s wreck once it is found.

We tested both sonars over a known shipwreck located 17.9 kilometres ENE of Cape Moreton that is often confused as the wreck of the Centaur. The SS Kyogle was sunk in this location in 1951 by the RAAF who had used the hulk for bombing practice. Although this information has been known for many years, in 1995 the wreck of the Kyogle was claimed to be the Centaur and this belief persisted until 2003 when the wreck was properly investigated and shown to be unlike the Centaur in a number of important ways. The main difference was in size: the Centaur was 95 metres long and 3,222 tonnes while the Kyogle was only 55 metres long and 702 tonnes.

The wreck we imaged during our sea trials last night measured to be about 55 metres long, 10 metres wide and only 4 metres high. The wreck is intact, sitting upright and there are no other large sections of wreckage nearby. Clearly this is the wreck of the Kyogle and not the Centaur as many had believed and still do. 

Tuesday 15 December 2009 

Day two of the search

Day two of the search

This bathymetric map shows just how irregular the seabed is within the search box. The pink/red colours to the left represent shallow water of about 300 metres depth while the purple colours to the right represent the deepest waters of in excess of 3,500 metres. (Courtesy of Dr. Ron Boyd, CSIRO) (seabed-map.jpg)

Earlier this morning we completed the second trackline through the designated search box, which was run on a course heading of 160 degrees true. The ship is now in the process of turning towards the start of the third trackline on a reciprocal heading of 340 degrees. Because the SM-30 sonar towfish is being towed from the end of a 10,000 metre cable with as much as 8,000 metres of cable deployed at any one time it can take up to 6 hours to complete a turn and resume searching. There are several techniques we can use to reduce turn times seeing that they are essentially non-productive periods, however this has to be balanced against the need to properly align the ship and sonar towfish for the next trackline.

If this sounds a bit boring that is because searching for shipwrecks can often be a boring and tedious routine of line, turn, line, turn, line, turn… day after day with nothing to see on your computer screens but endless fields of flat and featureless mud. That, however, is not our experience on this search. This section of Australia’s continental margin is geologically very dynamic with steep canyons carved into the continental slope. We owe this knowledge, and the detailed terrain map of the seabed that is helping us guide a safe path for the SM-30 towfish, to a group of CSIRO scientists who came out here last year to map the area because of its geological interest.

Like them before us we have found our search box to be dissected by three large submarine canyons whose walls rise 600 metres or more to exposed rocky cliff tops. The impact of all this geology is that it makes our job of picking out a relatively small shipwreck like the Centaur amongst all the rocks extremely difficult. We saw just how difficult this was on the last trackline as we estimate that roughly 30 percent or more of the seabed along that line was virtually unsearchable: meaning that even if our sonar passes right over the wreck it may not be able to detect it amongst the rocks and large “acoustic” shadows where the sonar signals are unable to penetrate.

I have included two sonar images with today’s diary to show the difference between what a smooth section of seabed looks like compared with a rocky section. It doesn’t take a degree in geophysics to see how much harder it would be to find a wreck on the right side of the rocky image. Keep in mind when viewing these images that the scale is huge (about 5,500 metres across the entire image) so the wreck itself is only going to be relatively tiny feature.

It is not all gloom and doom though. There are still great swathes of relatively flat and featureless seabed in the high probability sinking area and we did pick up a promising target on the first track line that I will want to take a second look at. The target was very close to directly beneath the sonar towfish where it doesn’t perform as well. Nevertheless the target was about the right shape and size of the Centaur so we definitely have something to look forward to in the days ahead. First, however, I want to make the most of the favourable weather and currents we are experiencing to search a few more lines in the search box before re-directing our efforts towards this promising target. The East Australian Current is definitely picking up speed past our location so we may not have these ideal conditions much longer. 

Wednesday 16 December 2009 

Day three of the search

 Day 3 of the search

Aaron Smith uplinks the video footage he has shot to an overhead helicopter via a special microwave transmitter.

A Brisbane based news helicopter has come out to visit us twice since the search began. All the National news broadcasters have agreed to share the pooled video footage shot by Aaron.

News helicopter

As I write today’s diary we are nearing the end of the fifth of fifteen tracklines I have established to more than completely cover the designated search box. My aim with this plan is to achieve 200 percent coverage of the search box, meaning that all areas (and targets) will be investigated at least twice. The 15 tracklines form a grid pattern in which there are 10 primary tracklines and five “gap” lines, all overlapping to a large extent.

The function of the “gap” lines is to cover the area directly beneath the SM30 sonar towfish, which, because of the physics and geometry of a side-scan sonar, is not well covered. This is why we call this area a gap, or “blind spot” and it needs to be filled before we can claim an area to be completely searched. The most important thing in a search like this is to ensure that all areas of the search box are covered and there are no gaps or holidays in the coverage.

My plan over the next 24 hours is to search two more primary tracklines before investigating the best sonar targets we have seen up until that time. So far we have found two targets that are promising enough to warrant a further look with a higher resolution setting of the SM30 sonar. While these two targets are roughly the right size and shape of the Centaur, I would not want to give the impression that we believe we may have found the wreck as some press reports have speculated. If any target we find at any time completely fits what I am looking for in terms of matching the characteristics of Centaur’s wreckage then I would divert the search immediately to investigate such a target. The two targets we have already found don’t quite fit that bill and for this reason the search continues.

You may be wondering how we have been able to get video footage of the search’s progress off the vessel and on to the TV. I have included a couple of pictures today to show how this is being done. We have been kindly loaned a microwave transmitter that our videographer, Aaron Smith, uses to upload the video he shot over the previous days to a news helicopter hovering a few hundred feet over our heads. While the helicopter is hovering I have also been able to give an interview to the reporter sitting inside. This method has worked perfectly and we are planning another video uplink and interview after lunch today.

Finally, I would like to thank the members of the public who have been writing in with their notes of appreciation for our efforts. I make a point of sharing this feedback with everyone on board as it gives them all an extra sense of purpose and motivation to do their jobs well. The comments have been overwhelmingly positive and I sincerely hope we will be able to reward the great amount of public support we have received with a successful location of the Centaur. 

Thursday 17 December 2009 

Day four of the search

Day four of the search

Williamson & Associates team of sonar operators at their stations monitoring the incoming sonar imagery. This is where they “fly” the sonar towfish over the seabed by remote control of the large towing winch on deck.

My plan for today was to tow the SM30 sonar past the most promising (there are now five in total) sonar targets on a higher resolution setting to rule them in or out as being the Centaur. However in planning these tracklines it became apparent that to obtain the best imagery possible we would need the lines to be run from the north even though the ship, having completed the last primary trackline, was at the southern end of the search box and thus out of position. Because the multiple turns required to line up the high-resolution passes when approaching from the south would have wasted many hours I decided to run one more primary trackline to the north, which would then put us in the ideal position early tomorrow morning.

Another factor in this decision was the troublesome East Australian current (EAC) as we are now feeling the full force of this famous boundary current.  During the search last night the EAC was running at 2 knots and the ship handlers were only just able to keep the Seahorse Spirit on track using every inch of their skill and concentration. To the displeasure of those sleeping in Spirit’s lower decks, her bow and stern thrusters were noisily engaged most of the night to steady the ship sideways as she “crabbed” down the line at an angle of 45 degrees.

Since then the EAC has picked up even more strength and during the course of writing this diary it has increased from 3.2 to 4 knots. We have been very fortunate not to have lost any time due to the current but my concern is that our luck has run out.

Friday 18 December 2009 

Contingency plan in place for lost sonar 

At approximately 0330 this morning (Friday, 18 December) the signal from the SM30 side-scan sonar towfish was suddenly lost. Recovery of the 2000 metres of towcable deployed at the time commenced immediately, however it ultimately became apparent that the mechanical termination that couples the towcable to the SM30 depressor and sonar towfish had failed and that both units were lost in water depths of approximately 1800 metres.

The failure occurred whilst the sonar towfish was in the midst of a turn in preparation for making the high-resolution pass over some of the most promising sonar targets found to date. Efforts are underway to make acoustic contact with an emergency transponder mounted on the towfish. If communication with the transponder can be made it will be sent an acoustic trigger to release the sonar towfish from the depressor after which it will float to the surface for eventual recovery. This emergency release system is a built in feature of the SM30 and the Williamson & Associates team on board have made several such recoveries in the past from similar water depths. The team also have alternative options for recovery should acoustic contact with the sonar towfish not be made.

In the meantime the search for Centaur will recommence with only a short delay to reterminate the towcable and prepare the AMS60 sonar for launching. I am fully confident that, if need be, the remaining search area can be covered using the higher-resolution AMS60 sonar. Its ability to provide excellent images of a shipwreck has been proven during the sea-trials over the SS Kyogle and in the location of HMAS Sydney and Kormoran last year.

One of the reasons Williamson & Associates was selected as the search contractor for this project was because they are the only firm in the world that provides a complete spare sonar towfish, towcable and winch for full redundancy of these critical components. As part of our project planning we also allowed a contingency for just such events so the impact of this loss on the overall project schedule should be relatively minor.

There can be little doubt that the extremely high currents we have experienced over the past couple of days was a factor in this loss and it confirms our expectations of just how difficult the conditions are out here and the challenge they pose to the search team and equipment.

Saturday 19 December 2009 

Day six of the search

Day six of the search

Secured by taglines the AMS60 sonar enters the waters of the Coral Sea. When fully immersed the towfish is slightly positively buoyant and at this point the main lift line to the crane can be released.

The Williamson & Associates team made a quick recovery from the disturbing loss of the SM30 sonar towfish yesterday and we were back in the water by 1720 hours resuming the search with the spare AMS60 sonar. The main difference between the two sonars is their frequency of operation and resulting resolution. The AMS60 sonar operates at the higher frequency of 60 kilohertz which enables it to collect correspondingly higher resolution images. In simple terms we will be able to “see” the targets better with the AMS60 and thus have a better idea whether the targets are man-made or geology. So while the loss of the SM30 was very unfortunate the AMS60 is the best option for this next phase of the search.

Out first set of high-resolution tracklines past the six (we added another one the day before) promising sonar targets was successful in that we were able to eliminate five of the targets straight away as being geology. That left one sonar target, which in my estimation looked even more promising compared to when we first imaged it on our very first trackline. The target has the right approximate shape and size for the wreck of Centaur and importantly we could now see an acoustic shadow behind the target whereas in the original image there was none. The target also fell squarely within my high probability area centred on Gordon Rippon’s dead-reckoning position and that is obviously another positive indicator.

While the identity of this target is still uncertain it definitely deserves further investigation with more high-resolution sonar runs and that is what we will be doing today. I have been fooled in the past by rock formations that look just like shipwrecks so until I am absolutely certain what this target is I won’t be jumping to any conclusions. There is an awful lot of geology filling up our sonar displays so picking out a solitary and relatively small shipwreck amongst the fields of rocks has to be done with the utmost care and caution.

Sunday 20 December 2009

 The Discovery of the Centaur

Discovery of the Centaur

The last of eight different high-resolution sonar images we collected to make sure the target was indeed a shipwreck. The wreck is the long dark blue shape while the adjacent acoustic shadow is burgundy in colour. Close examination of the image indicates that one or possibly two breaks in the hull.

On behalf of the search team and marine crew on board the Seahorse Spirit I am delighted to confirm the announcement made earlier this morning that the wreck of the Australian Hospital Ship Centaur has been found. While photographic proof of the find will have to wait until the ROV phase of the project is assembled early in the New Year, we have collected a series of sonar images that are without doubt from the Centaur.

Before providing the specifics of the wreck location I would like to praise the enormously skilful efforts of the entire team that achieved this important result. This search was possibly the hardest and most technically demanding I have ever been involved in. The reason for this was the difficult seabed and current conditions I have written about in my previous diaries. The ship handling ability of the Captain and Officers of the Spirit was easily the best I have ever seen. This mornings’ sonar pass, which confirmed the location of the wreck, was conducted while the Spirit was broadside to a 4.2 knot current yet the ship was kept perfectly on the trackline we requested. Similarly, much of this success is due to the talented crew of Williamson & Associates for their initial detection of the wreck and for producing the remarkable images I demanded were necessary to prove the wreck’s location.

The Centaur lies in one piece on the lower flank of a narrow gulley, which measures 150 metres wide and about 90 metres deep and is bounded by steep walls on either side – one with a slope of roughly 45 degrees. To collect the final sonar images of the wreck the AMS60 towfish had to be flown within the gulley well below the level of the walls on either side. While the wreck is intact Centaur’s hull appears to be partially broken in at least one and possibly two locations. No doubt the torpedo strike would have caused one of these breaks. There is also a distinct possibility that the wreck is lying on its side. There is a very small scattering of debris around the wreck, much less than I have normally observed with a ship sunk by torpedo.

The approximate position of the wreck is 27°16.98’S, 153°59.22’E at a depth of 2,059 metres. Remarkably this position is less than one nautical mile from the dead reckoning position I calculated from Gordon Rippon’s track. I can’t remember finding a wreck as close to the position reported by a primary source witness, which proves just how precise Rippon’s navigation was. Before the search commenced there were serious and legitimate questions posed about whether Rippon could have actually seen Pt. Lookout light from the 23 nautical mile distance that formed the basis of his navigation. However, the close proximity of the wreck to Rippon’s track is about the best testament you could make to man whose life was spent navigating the high seas

Saturday 9 January 2010

Commissioning sea trial at the wreck of the Kyogle

Commissioning the sea trial

Kyogle’s twin propeller mounts (minus the salvaged propellers) on either side of its elliptical rudder.

The 3 hour commissioning sea trial of the REMORA ROV system was completed at 12:15 pm today having successfully filmed the wreck of the Kyogle shipwreck at approximate position 26° 59.32’ South 153°38.58’ East.

The Seahorse Spirit is currently underway to the wreck site of AHS Centaur and we expect to arrive there by 1645 hours.

The ROV came upon the Kyogle from the bow and it was immediately apparent that its straight bow was different to Centaur’s slightly raked bow. The Kyogle is heavily damaged due to a combination of factors including the gun-fire and shelling it suffered at the hands of the RAAF in 1951 when it was used for target practice and then scuttled, the fishing nets that for many years have been dragged over the top of the wreck, and general corrosive action that is slowly but surely reducing its steel hull to a pile of rust.

As schools of fish swarmed around the ROV it was eventually piloted towards the stern of the wreck where conclusive proof of its identity was found. Although the Kyogle’s valuable bronze propellers were removed before she was scuttled we saw that there were indeed two propeller mounts on either side of the Kyogle’s elliptical rudder. The Centaur, in contrast, had only one propeller and a plate-shaped rudder. Hopefully our photograph of Kyogle’s twin propeller mounts, when compared to the attached construction drawing showing Centaur’s single propeller will remove any and all doubts from people’s minds.

Sunday 10 January 2010

 Visual confirmation of the wreck of the Centaur

Visual confirmation of the Centaur

This is an overview photo of the red cross on the port bow between the green band. The red and green colours are not apparent because the ROV is still too far away from the hull to illuminate the scene properly.

At 0250 hours early this morning visual confirmation of the wreck of 2/3 AHS Centaur was obtained, which will hopefully end a 66-year quest for unanswered questions and bring comfort to many families across Australia and beyond.

As expected from the sonar imagery the wreck was found leaning over towards its port side at an angle of approximately 25 degrees and the bow is almost completely severed from the rest of the hull in the area where the single torpedo hit. Although the wreck is very badly damaged, characteristic markings and features that identify the wreck as the Centaur were clearly visible. These include:

  • The 4-foot wide green band painted around the entire hull
  • The large red cross visible of both sides of the bow
  • The number 47, painted white on a black square, that designated the Centaur as Australian Hospital Ship 47
  • The paravane (for cutting moored mines) mounted on the starboard bow
  • A raised star on an oval plate which marks the ship as being a Blue Funnel ship

Because of a minor problem with one of the Seahorse Spirit’s main engines we had to limit the time of this first ROV dive and thus focused on identifying the wreck as the Centaur. Additional ROV dives will be required to completely document the shipwreck owing to her bad condition. The conditions for filming the wreck are also not as good as I would have liked, in part because of relatively strong seabed currents that are causing “dust storms” of particulate material that are obscuring our camera vision.

While we have a number of hard days ahead of us to complete the filming work I would like to take this opportunity to thank and congratulate all the people involved in the project that have made it a success and to express my sincerest appreciation to the countless others who have campaigned for and supported this quest from the very beginning. 

Tuesday 12 January 2010

 Memorial for the AHS Centaur

Centaur memorial

The memorial plaque on Centaur’s bow.

At 0555 hours early this morning the memorial plaque entrusted to us by the 2/3 AHS Centaur Association was gently placed on the fore deck of the wreck of the Centaur. Incorporated in the plaque was a Roll of Honour with the names of all 268 men and women who perished when the Centaur was sunk. This plaque serves as a headstone for those entombed in this maritime grave.

The location where the plaque was laid – just starboard of the forward (No. 1) hatch opening – was chosen because it was deemed to be the most visible and permanent in keeping with the wishes of the Centaur Association. Special care was taken to ensure that the 29 lb bronze plaque would not damage the wreck in any appreciable manner. Approval for the plaque to be laid directly on the wreck was granted yesterday on an urgent basis by the Department of the Environment, Water, Heritage and the Arts in the form of a permit (No. 14 to David Mearns) under the Historic Shipwrecks Act 1976.

Following the plaque laying we spent another four hours filming individual pieces of wreckage found in the small debris field immediately adjacent to the wreck. During this dive more personal items were found including ankle boots (with the laces intact), a trunk of personal belongings and another felt slouch hat. The slouch hat was an amazing discovery that appears to have had as much of an impact on everyone on land following the media coverage of the search as it had on us on at-sea.

Today at 12:30 pm a brief memorial service was held over the site of Centaur’s wreck with readings and prayers by Major Arthur Dugdale, Historian John Foley and Graham Samway Captain of the Seahorse Spirit. At the conclusion of the service Major Dugdale laid a wreath on the water over the site. The entire ship’s company and all search personnel were present on the aft deck of the vessel during the service.

The at-sea search for the Centaur is now finished. In addition to the successful location of the shipwreck at a depth of 2,060 metres very close to the position indicated by Centaur’s navigator Gordon Rippon, the expedition yielded approximately 1,400 still photographs and over 20 hours of high-definition video footage of the shipwreck and its surrounding environment. Hopefully this information will help keep alive the memory of the brave men and women who sacrificed their lives in service of their country.

I consider it one of the great privileges in my life to have led this important project.


1 Response to David Mearns’ Search Diary

  1. Helen Vann says:

    I have just moved to the Sunshine Coast and found the Centuar Memorial at Caloundra today. I was unaware of this terrible event and am utterly moved by your account of finding the wreck. May all the personnel who went down with the ship rest in peace.

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