Excavation of the Batavia Wreck Site

1. The Wreck Site

The Batavia wreck site is located on Morning Reef in the Wallabi Group of the Houtman Abrolhos - a series of islets and reefs lying between latitudes 28°14' S and 29° 00' S and longitudes 113° 35' E and 114° 04' E, about 35 km from the mainland of Western Australia. There are four groups of islands within the Abrolhos: North Island; Wallabi Group; Easter Group and Pelsaert Group. They represent the southern-most well developed coral reef in the Indian Ocean.

Beyond the main site in the lagoon shallows, on the inside of the reef is an area about 500m long by about 200m wide where material from the wreck has been driven by storms. This area is referred to as the ‘inside reef site’. Depths in this area range from 0.5 to 2m and artefacts consist of large numbers of fragments of stoneware, bricks, some remnants of chain plates and odd coins.

The main site on the outside of the reef, is about 50m long and 15m wide. At the north end of the site, closest to the reef are three large anchors, with a fourth 78m further north in the shallows on top of the reef.

Along the western side of the site, twenty-one iron, five bronze and two composite cannons were located when the site was first discovered. Prior to the start of the first season, three iron, one composite and all five of the bronze cannon had been raised. Another group of four anchors were located about the mid-point, on the east side of the wreck site. Slightly to the south of these anchors, across the site were a pile of shaped building blocks.

Large stone next to some submerged timber planks

Stone portico block amid the timbers at the wreck site
Image copyright WA Museum

2. The Facilities

Beacon Island was the base for the excavation. A small house was constructed to accommodate six people, with a workshop, storage shed and a small darkroom built nearby. As there was no fresh water available on the island, three large catchment tanks with a total capacity of 10,000 litres were used to collect rainwater from the roofs of the buildings in the winter rainy season. Since the excavation seasons took place in the rainless summer, water restrictions were necessary.

A jetty was built from the north-east end of the island, next to the station, out to a deep water passage. This allowed our work boat to unload directly onto the island and enabled the island supply boat, and other large vessels to come alongside to be loaded with heavy material. A davit, with a lifting capacity of about 0.5 tonne was built on the end of the jetty to enable heavy or bulky objects to be loaded or unloaded from the boats.

During the period from August to February, the Abrolhos are uninhabited, thus when working during these times, fresh fruit and vegetables were flown out by sea-plane once a fortnight, together with mail and newspapers. The aircraft also served to change-over staff, and was available for emergencies.

The period from February to August is the Abrolhos crayfishing season, during which several hundred fishermen, with their families, live in huts on the islands. A supply boat visited Beacon Island every two days during this period bringing provisions for our team and the four families involved in fishing.

A hand holding five large silver coins

Silver coins salvaged from the wreck site
Image copyright WA Museum

3. Excavation Conditions

Cyclones are most commonly expected in this area between January and March. Three cyclones were experienced during the four seasons of work on the site, none of which caused serious damage, the only problem being to secure a mooring for the workboat.

The main excavation work was carried out from Henrietta, an 11m long steel work boat powered by twin turbo-charged diesel engines. This vessel was specially designed to the specifications of the Department of Maritime Archaeology for this type of work. Two small 5m aluminium dinghies were used for running around the islands and working on the inside reef.

The greatest problem working on the Batavia site is swell from the south-west, which is generated in the Indian Ocean. The swell builds up over a number of days, from flat calm to swells with breaking crests over 10m high, which gradually increase the danger of the workboat being swamped on its mooring. The use of two mooring points, 50m and 75m from the site, enabled the work boat to operate on the site in both rough and calm conditions.

In all cases, the greatest danger was always related to the workboat and thus, at all times the vessel was securely chained to the mooring. Diving was invariably terminated because of the danger to the work boat due to increasing swell, rather than difficulties or dangers to the divers.

During the four seasons of work on the Batavia, a total of 447 days were spent on site. Due to bad weather it was only possible to dive on the main site on 170 of these days, during which time a total of 1617 diving-hours of underwater work was logged, and an additional 500 hours was logged working on the inside site. 10 diving-hours per diving-day were spent on the main site, this occurring on an average of one day in every three. During bad weather periods, time was spent at the base camp on Beacon Island photographing, drawing and recording artefacts.

4. Artefact Recording

General Recording

The record of the progress of the excavation, wind, weather, sea state, diving-log and other associated matters, were recorded in a daily diary. Archaeological notes were kept on the page opposite the record of the day, together with photographic data, survey information and technical notes. The artefacts were recorded in finds books and were designated an arbitrary prefix number to identify material type, thus:

1. Stone

2. Ceramic

3. Non-ferrous

4. Miscellaneous

5. Coin

6. Timber

8. Ferrous

The location of the find-spot of the object and the date of recovery, together with any other relevant information was also recorded. Where possible, identifiable objects were photographed and drawn on plastic drafting film with Indian ink at a 1:1 scale.

Studying the artefacts immediately at the field station was useful, particularly with ceramic material, as it was then possible to return to the find spot to search for missing pieces.

Underwater Recording

It was difficult to make accurate taped measurements because of the strong surge. Therefore a simple system was adopted consisting of a taut wire base-line run out over the long axis of the site with a sliding right angle frame constructed to run through the base-line. Objects were coordinated by sighting along the arm of the frame at right angles to the wire. By measuring the distances along the wire and along the right angle arm to the object, it was possible to determine its position.

Additionally, a contour map of the wreck site was made by running a series of seven parallel lines three metres apart, along the long axis of the site. Depth measurements were made at 1m intervals along each line with a Bourdon type depth gauge. The results were transferred to the plan of the wreck site, from which contours at 1m intervals were constructed.

Timber Recording

Each piece of the ship’s structure was tagged in-situ. The tagging system used a coded number, with a prefix letter to identify the type of component. Six basic layers were distinguished in the side of the ship and these were coded alphabetically from the top to bottom, corresponding to the inside (top) to the outside (bottom). The numbers differentiated timbers in particular layers. Thus:

A. Knees, decking, deck beams and everything on top of the ceiling

B. Ceiling

B. Thin skin on top of B

C. Frames

D. Inner layer of strakes

D1. Thin skin on top of D

E. Second layer of strakes, lying below or on the outside of D.

F. Sheathing

T. Stern structure.

As each layer of timber was uncovered, it was tagged, photographed, raised and returned to the base camp. Here, each individual piece of timber was given a registration number, identified, and then stored in sea water tanks. During bad weather periods, the timbers were removed from the tanks, drawn, photographed, and then returned to storage.

Drawings of the timbers were made by tracing the surface shape and features onto thin gauge polythene sheeting. Where necessary, drawings were supplemented by photographs. Speed was essential in this process, as there was a danger that the timber might warp or crack with exposure or during transport.

Underwater Photographic Recording

Three types of photographic recording were carried out on this site: site photomosaic, timber photomosaic, and stereo recording.

Site Photomosaic:

A photomosaic of the whole wreck site was made at the start of the first season, to supplement the site plan. Seven taut parallel lines 1m apart and 46m long were taped with black PVC tape at 1/2m intervals to form a scale and laid along the long axis of the wreck site. Photographs were taken at 1m intervals along each of the lines.

Timber Photomosaic:

As areas of the ship’s structure were uncovered, individual timbers were labeled and photographs were made of all exposed areas of each timber. The surface layer of timber was then removed and the underlying layer was re-tagged where necessary and a second mosaic was made. In this way, a series of photomosaics of the individual layers of the structure were obtained over the entire area of the site.

Stereophotography:

was employed to aid in interpreting the photographs of the structure in complex areas of the site. The additional dimension this provided meant that an apparently featureless area of seaweed and concretion, when viewed with stereoscopy, immediately revealed the position of cannon balls under concretion and other three dimensional features.

Photographic Recording on Land

At base camp during the bad weather periods, each individual timber was brought out of the sea water tanks for drawing and photography. Indirect light was the best type of lighting for photographic recording of surface details of the almost black timber. An open-ended shed provided shade from direct sunlight. In the roof of the shed, 2 m above the ground, a Nikon F reflex camera was mounted and levelled with a spirit level. The timbers were wheeled in on a trolley and positioned directly below the camera, using a spirit level to ensure the plane of the timber was uniform over the whole object. With large or long timbers, a series of overlapping photographs were taken by moving the trolley under the camera to make up composite images.

Diver performing research on submrged timber

Timbers tagged in-situ
Image copyright WA Museum

Diver holding an early underwater camera

An early underwater camera
Image copyright WA Museum

5. Excavation

The First Season

The prevailing direction of the swell and surge is along the axis of the site, driving loose material north towards the reef. Before the excavation started, the surface of the site was loosely concreted together with coraline algae to form a crust. Once this crust was broken there was a tendency for the loose material below to be scoured out during storms. Thus the excavation had to be carefully planned to take this into consideration. The stern area was selected as the most obvious starting point, particularly as this was the easiest area to work; the bow area was more turbulent and less often suitable for diving. As the complex of anchors and cannon 10, 11 and 12, in the middle of the site formed a barrier to scouring, it was decided that this would be the northern-most limit of excavation.

Digging a trench on this site was out of the question, since any resemblances to trench walls were rapidly scoured out. It proved most feasible to clear an area systematically, gradually lowering the level by removing the coral lumps and building blocks in the area. As the cleaning operations progressed westwards across the site, the number and quality of the artefacts increased, and several complete stoneware jugs were found around cannon 5. Cannon 5 was removed from on top of the timber, which then showed the structure sloped downhill towards the aft area of the wreck site.

At this point, because of the danger of storms destroying the uncovered timbers, it was decided to dismantle the structure and raise it. The ribs were removed and raised in the lifting tray, after thirty had been tagged and recorded. The strakes were then tagged and photographed. It was found that the outer planking consisted of two layers of strakes, with a further outer layer of thin pine sheathing.

Towards the end of the first season, the area around cannon 1 and 2 was cleared of coral, and cannon 3 was raised. The last of the timber was recorded and raised. At this point, 5.5m of timber had been recovered. The rest of the timber was covered with plastic sheeting and several hundred bags of coral, and the excavation was wound up for the winter.

The Second Season

The first phase of this season was to clear the concretion overlying the timbers. This proved to be extremely difficult, because the concretion contained a large number of iron cannon balls, and as they were cleared further aft, the concretion became thicker. From a series of experiments it was found that the use of small explosive charges (circ. 10 grams) was the most satisfactory technique. Following each charge, the loose cannon-balls were excavated and the broken concretion spoil was airlifted off the site. Many delicate iron artefacts were recovered from this concretion, including bar shot and iron spoons. The ceiling planking was sawn through, and raised. The ribs were then removed, and finally the outer strakes were cut through with the chain saw and raised.

The excavation then proceeded further aft, and cannon 1 and 2 were raised. Once these were clear, five large lodging knees were uncovered running at a slight angle to the strakes. The cannon ball concretion lay over and in between these knees, which made extraction difficult. The western-most knee and thus the highest on the side of the ship, lay directly under cannon 2. The cannon ball concretion started east of the next knee, as it was assumed that this was some sort of stern shot locker. Complex decking in this area was noted, presumably the floor of the gun deck. The cannon balls had therefore spilled across the side of the ship when it rolled over on its port side. The deck acted as a barrier, preventing the cannon balls rolling further west.

Progress during this season was very slow, mainly due to the enormous quantity of coral and concretion that had to be cleared in the stern section. A systematic programme of collecting pottery and bricks on the inside reef site was started and quite a large collection of mainly stoneware was made from this area. This work was carried out during times when it was not possible to dive on the main site.

The Third Season

After removing the protective cover from the stern timber area at the start of the season, the remains of the stern post was discovered. The post had water line markings and the whole post was carefully recorded and raised. Work continued on removal of the transom lodging knees. This aspect continued to give rise to problems as the cannon ball concretion extended down the narrow gaps between the knees, firmly wedging the knees in place. Work proceeded slowly as this concretion was carefully chipped out, following the use of small explosive charges. The ceiling was recorded and removed as the lodging knees were raised.

Finally, when all the knees were freed and raised, the remaining ceiling planking and ribs were raised. As the outer planking ran behind the fashion piece, it was necessary first to remove the wing-transom, and transom beams before removing the fashion piece. After removing the transom beams, the diagonal stern transom planking was exposed. The fashion piece was freed and raised. This was the largest single timber item recovered, being over 4 m from end to end, 0.3 m thick and about 0.5 m wide. It is estimated that its weight was about one tonne. After removal of the fashion piece, the outer planking was found to be arranged around the transom in a curious fashion. The inner layers of the strakes were butted up against the inner transom planking, under the fashion piece. However, the outer planking was bent around the transom in a continuous strake. These were removed and the excavation of the ship’s structure was finally completed.

The excavation work then moved into the area to the north of the old building block area, bounded to the east by the group of anchors and to the west by cannon 10. In the process of clearing coral in this area large numbers of coin were found, particularly to the west side. A large concretion containing iron and coins was raised. On breaking it up at the field station, an astrolabe was discovered in a fine state of preservation.

The excavation proceeded around the central lump, a small mound of coral and concretion about one metre high. Further to the north coins and miscellaneous finds were noted together with a large number of bricks. Before this area could be cleared, the excavation had to be terminated for the year.

Diver holding an undamaged piece of stoneware

Complete stoneware jug found
Image copyright WA Museum

A large cannon being raised onto a ship

Raising a cannon
Image copyright WA Museum

The Fourth Season

This season was started in September and it proved to be a very bad period for weather. During the season only 10 days work was possible on the main site. During this period, excavation was continued around the central lump. More cannon balls and some other miscellaneous artefacts were raised. Due to the bad weather, about 200 diving hours were spent on the inside reef collecting pottery and searching for new areas of wreck material.

A large timber framed lifted onto a ship

Raising the timbers
Image copyright WA Museum