The problem with some maritime sites is that they are only intermittently visible, and relocating them once they are recovered can require the use of specialised equipment such as a magnetometer; especially if the area is physically changing and you lack precise coordinates. Relocating an elusive wreck often requires as much work as finding one that has never been sighted – but it’s rediscovery can be met with underwhelming responses of ‘so what –someone had already found it!’
As part of magnetometer trials being conducted by the Department of Environment and Heritage Protection (Queensland) we thought it would be beneficial to examine two similar wrecks off the Gold Coast to determine how comparative signatures could be used to locate obscured wrecks. The first wreck is that of the Scottish Prince, an iron barque of 850 tonnes that ran aground in1887 and is now a popular dive site. The second wreck, the Cambus Wallace, is an iron barque of 1650 tons that also ran aground, but is now quite collapsed and usually covered in sand. The two are often referred to as the whiskey wrecks, as they were both carrying large consignments of bottled whiskey which were heavily salvaged by helpful locals keen to clear the beach of debris.
EHP maritime archaeologists and rangers from the Department of National Parks Recreation Sport and Racing (NPRSR) went out under overcast but calm conditions and commenced the survey over the known location of the Scottish Prince wreck. The north south transects took in a wide area around the wreck to ensure we could effectively assess the detection range. The side scan imagery and signal return during the survey were as expected, with a very strong concentrated magnetometer signal that was detectible up to 180 metres away from the main section of the wreck (see images 1 and 2).
Despite the Cambus Wallace being a larger and slightly later ship, its position closer to the shore and within the prevailing swell has meant that it has suffered considerably more damage and is now broken up. The wreck was relocated in the 1970s and artefacts removed from it; there have also been regular reports from people who claim to have historically fished it and people have regularly fished on it, however its exact position has remained elusive because it is only intermittently exposed and official position references are based on triangulations from land marks that no longer exist. It is also located near the surf zone and Jumpinpin bar, meaning it can only be safely surveyed and dived during westerly winds or in very calm conditions – which occur only periodically.
After completing the Scottish Prince geophysical survey, there was sufficient time to conduct a speculative survey for the Cambus Wallace. Interim transects were developed, but the very shallow nature of the environment meant that the skipper was forced to follow the submerged sand bank to avoid risk to the vessel and the mag.
A strong concentrated signal was located, although the return pattern was not as defined as the Scottish Prince (see Image 5). When the coordinates for the possible Cambus Wallace were cross referenced with historic aerial imagery, a clear darkened shape was intermittently visible approximately 200m from the magnetometer signal. The shape of the object was consistent with the dimensions and reported alignment of the wreck (see Image 6).
Although yet to be confirmed with a dive inspection, this is a very promising lead that corresponds with historic records and public information.
Although the magnetometer reading is strong and relatively confined, the strength of the signal is not as great as for the smaller Scottish Prince. If the signal does represent the Cambus Wallace, the slightly weaker signal could be indicating that the wreck is closer to shore where the survey vessel could not safely travel; this is potentially consistent with the aforementioned darker shape being the wreck. There is also the potential for the Cambus Wallace site to have a larger debris field, given the dynamic nature of the site environment and the more collapsed nature of the vessel’s upper deck. Certainly there is still work to be done, but if we confirm the signal is the Cambus Wallace, it will be an exciting ‘rediscovery’.