Ashmore Reef Expedition 2015 – Part Five

Overnight, the wind from the north-west has abated a little and the swell on the northern exposed edge of Ashmore Reef, where the wreck site is located, has decreased. This allowed us to get dive teams on-site nice and early to take advantage of the calmer seas.

Led by Michael Gooding (Silentworld Foundation), Lee Graham (Australian National Maritime Museum) and Grant Luckman (Department of Environment) the dive teams have continued to plot the scattered remains of the shipwreck by carrying out additional 100 metre-long compass and tape transit surveys from the two main anchor clusters.

With two teams working from the large anchors and one team working from the small anchors – and keeping an increasingly worrying eye on the wind as it began to strengthen as the day progressed – the site and its relative position on the reef top continued to be surveyed and the information compiled onto the overall plan of the wreck site.

As the divers became more familiar with the site and their eyes attuned to the sea bottom they began to pick out and identify a number of smaller artefacts mixed in amongst the broken shell, coral fragments and sand grains. These included 40mm long copper sheathing tacks, coral encrusted rolls of lead, basalt ballast rocks, smooth river worn sandstone and shingle ballast, fragments of dark green bottle glass, a round deck prism (a glass prism that is laid flush into the deck of a ship allowing the prism to refract and disperse light into a compartment below the deck), numerous pieces of copper sheathings and several larger copper fastenings.

Whilst the divers struggled with the increasing swell, John Mullen (Silentworld Foundation) and Frits Breuseker (Seasee Pty. Ltd.) bravely piloted Maggie II around the northern edges of Ashmore Reef.

Towfish is shown at apex of across-track beam of energy (yellow fan-shaped area). Previously ensonified area shown as light grey area, with corresponding image to features depicted below. Brown stripe below towfish shows the along-track dimension. Figure adapted from Able,1987. Credit: Woods Hole Coastal and Marine Science Center.

Credit: Woods Hole Coastal and Marine Science Center

Purpose built by the Silentworld Foundation, Maggie II is well-equipped. It has several magnetometers — instruments that calculate and record changes in the earth’s magnetic field caused by the presence of iron artefacts such as anchors, cannon, iron knees, anchor chain and so forth.

It also has scanning and side scanning sonar, which send out bursts of conical or fan shaped sound pulses down to the sea floor, which are then bounced back to the survey vessel after striking a submerged object such as ballast stones. These returned signals paint an acoustic picture of the seabed and can be interpreted on plotting screens.

Importantly, Maggie II has a differential global position system — an enhanced Global Positioning System that uses not only the normal navigational satellites used in conventional GPS, but also a series ground-based reference stations which broadcast similar signals from known fixed positions. The combination of the multiple sets of signals allows locational accuracy to be improved from the nominal 10 to 15 metre to about 100 mm.

With an eye on the sea state and another on the instruments, John and Frits magged and scanned the reef top and then the areas of sea bed to the north looking for any additional wreckage which may have drifted off into deeper water as the ship broke up on the reef.

By late afternoon the increasing wind, now gusting to 30 knots, had increased the size of the swell on the wreck site. Diving had become difficult and survey work impossible as the wind pushed rollers over the site, picking up and tangling tapes and pulling out datum and survey points.

Conditions back on board The Boss were not much better as it rolled heavily in the swell. After getting all the divers and tenders back on board we decided to cancel diving for the rest of the day and relocate the vessel to a safer and more secure anchorage.

Find out more in part six of the Ashmore Reef Expedition series.

Kieran Hosty
Manager – Maritime Archaeology Program

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About Kieran Hosty

I started diving in Western Australia in 1976 and after a few years of mucking around on shipwrecks joined the Maritime Archaeological Association of Western Australia in order to try and make sense of what I saw on the seabed. My love of diving and maritime history made me pursue a graduate degree in history and anthropology from the Western Australian Institute of Technology followed a few years later by a post graduate diploma in maritime archaeology from Curtin University also in Western Australia. After 18 months as an archaeological field volunteer I took up a position with the Maritime Archaeology Unit at the Victoria Archaeological Survey. I was the Commonwealth Historic Shipwrecks Officer in Victoria for six years before coming to the Australian National Maritime Museum in 1994 to take up the position of Curator of Maritime Archaeology and Ship Technology. At the Museum I was responsible for the Museum’s maritime archaeology program as well as curating the Museum’s collection relating to convicts, 19th century migrants and ship technology. My expertise in convict related material was further enhanced, when I took up a temporary position as Curator / Manager of Hyde Park Barracks Museum for eighteen months in 2004 followed by a further 18 month contract at the Barracks where I curated an exhibition on the history and archaeology of convict hulks and another on the World Heritage listing of Australian convict sites. In 2012 my role at the Museum shifted focus when I became the Manager – Maritime Archaeology Program – reflecting an increased emphasis on the importance of the maritime archaeology program at the Museum. I have worked on many maritime archaeological projects both in Australia and overseas including the survey and excavation of the Sydney Cove (1797), HMS Pandora (1791) and HMCS Mermaid (1829), the Coral Sea Shipwrecks Project (sponsored by the SiILENTWORLD FOUNDATION and the ARC) and the hunt for Cook’s Endeavour in the USA. I'm the author of the book Dunbar 1857: Disaster on our doorstep, published by the Museum along with two books on Australian convicts and 19th century migrants published by McMillan.

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