Finding A Shipwreck You Can’t See: Detection and Survey Methods from Hinchinbrook Island

By Kurt Bennett

I have just finished a week-long field practicum in tropical Queensland. The field practicum took place on Hinchinbrook Island between the 7th and 14th of July. Five students (including myself) from Flinders University helped the Heritage Branch of the Department of Environment and Heritage Protection (QLD) locate possible shipwreck sites. Multiple survey methods were employed to locate cultural material buried beneath the sand. This blog will focus on one site that was investigated during the field practicum. It is located on the north end of North Shepherd Bay (Figure 1).

Figure 1: Location of the ‘possible’ shipwreck and our campsite (Google 2013).

Figure 1: Location of the ‘possible’ shipwreck and our campsite (Google 2013).

Queensland Parks Service observed timbers in North Shepherd Bay after Cyclone Yasi, in 2011, removed sand from the beaches on the eastern side of Hinchinbrook Island. The GPS (Global Positioning System) coordinates were taken and passed on to Paddy Waterson, Senior Heritage Officer at the Heritage Branch. The pictures taken by Parks resembled possible ships timbers. On Monday the 8th July and Friday the 12th 2013, the GPS points were visited. The GPS points were located approximately 3.6 kilometres (km) from our campsite (South Macushla) along a walking track. The walking track finished on the southern end of North Ramsey Bay and required a 1.6 km walk along the beach to the approximate area. No cultural remains were visible upon arrival and therefore certain archaeological methods were needed to locate the previously seen cultural material. The following will discuss the methods employed in order to find the cultural material and determine what remains on the beach.

The first step was a mixture of two methods using both a GPS and a metal detector. The aim was to locate the original marks with the GPS and establish a central point for what was originally witnessed. A 20 metre (m) square was placed around the central GPS point, marking an area to be metal detected. The metal detector, Excalibur II, was set to exclude non-ferrous metals. This enabled the metal detector to detect iron concentrations. The metal detection was systematically executed, with the user following an east-west pattern every one metre along the 20 m grid. Every ‘hit’ was marked with a pin flag and measurements taken using the baseline offset method (Figure 2).

Figure 2: Metal detector hits with baseline. Photo facing NE, North Shepherd Bay (Kurt Bennett, 8 July 2013).

Figure 2: Metal detector hits with baseline. Photo facing NE, North Shepherd Bay (Kurt Bennett, 8 July 2013).

Once the designated area had been covered and all the hits were marked, the next step was to probe the points of interest (hits). This was to determine whether solid material was buried beneath the sand. Both metal and wood were detected, with metal being distinguishable from wood due to the vibrations and the sudden jolt felt by the probe, as opposed to the stickiness felt with waterlogged wood. The probing also indicated the depth of cultural material. The wood and metal was located at a depth of approximately 30 centimetres (cm) below the sediment surface. The sand proved to be a challenge to probe as it was wet and compacted due to being located in the intertidal area.

Once the probing indicated there was material below the beach surface, a 1 m square was placed around the GPS point; this also proved to be a concentration of iron from the metal detection survey. The trench was then excavated with shovel and trowel until material was found. Timber was uncovered, which was possibly a ship’s timber with an iron brace and a treenail (Figure 3). Photographs and measurements were taken of the timber. The trench could not be excavated any deeper than 30cm due to water seepage caused by the intertidal zone. Therefore only the top face of the timber and iron brace was seen, with the rest left submerged in watery sand. The trench also uncovered rocks that were thought to be metal when detected by the probe. This posed a challenge when trying to distinguish between metal and rock, as the rock had the same reaction as metal when probed.

This became more evident when the site was revisited on Friday the 8th.  Photographs were taken of the uncovered timber and the trench was backfilled. Our investigation was limited due to the tide and daylight dictating the time we could spend at the beach. The trench could not have been dug if the tide was in and therefore the site had to be visited during low tide. This left the team approximately four hours to investigate the site. Not to mention we had to be back at camp by nightfall for health and safety reasons. Apparently dusk is the time that crocodiles come out to feed, and that is definitely not the way I planned on finishing my field practicum.

Figure 3: One metre square excavated showing ships timber, North Shepherd Bay. Timber being measured by Flinders students (Kurt Bennett, 8 July 2013).

Figure 3: One metre square excavated showing ship’s timber, North Shepherd Bay. Timber being measured by Flinders students (Kurt Bennett, 8 July 2013).

North Shepherd Bay was revisited on Friday the 12th and this time the aim was to establish the full extent of the site. Again the metal detector was employed and this time we extended our square to 20 m north south of Monday’s metal detection area. To our disappointment the hits did not resemble the shape of a ship’s hull, but more a scatter of debris. This was still exciting, as it could still resemble a wrecking event. The only way to find out was to dig and dig we did!

Several holes were dug, with the longest being over four metres in length (Figure 4). This trench was a continuation from the previous ship timbers. Two additional timbers were uncovered and what appeared to be the beach substrate with a rocky base. It proved to be a little frustrating, since we set out to find a shipwreck. The timbers uncovered were measured and detailed drawings were produced, providing an accurate recording of what had been found. The lengths of the two timber were approximately 1.5 m. The rest of the metal detector hits uncovered a mixture of items that may have washed in over time, including a chain block and pulley, and buried car batteries. The metal detection survey was extended a further 250 metres, walking south along the beach, but it had to be cut short due to daylight running out.

Figure 4: Red arrows indicating points of interest dug for material. Photo facing SE, North Shepherd Bay (Kurt Bennett, 12 July 2013).

Figure 4: Red arrows indicating points of interest dug for material. Photo facing SE, North Shepherd Bay (Kurt Bennett, 12 July 2013).

The aim of visiting North Shepherd Bay was to investigate the known GPS marks. The timbers uncovered and seen after the cyclone may be a result of washed up material, possibly from a shipwreck in another location, or they could be the last remaining pieces of a shipwreck. The methods employed were systematically executed to try and determine if a shipwreck lay beneath the sand, however our thorough searching and non-stop digging proved it was a beach littered with cultural material that could span a whole century. The methods mentioned above will provide a basic plan for any archaeologist wishing to investigate buried shipwrecks on a beach.

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