Page 34 - Loss of the VOC Retourschip Batavia, Western Australia, 1629

Excavation tools
A number o f quite simple, but ingenious tools or aids
were used to assist in the excavation. Removal from the site of large quantities of coral was one of the biggest problems. The whole site was covered with a thick layer of dead coral, often up to 2 m deep. The coral was generally too large to be air-lifted; the largest lumps were plates about 1 m in diameter, and 0.5 m thick, ranging in size down to small nodules 100 mm in diameter. The surface layers of coral were lightly concreted together with cora- line algae which could be easily broken with a crowbar. With more stubborn concretion, a geological hammer was used as a hand-held chisel and this was struck with a short- handled sledge-hammer. The "hammer and pick" tech- nique was found to be the most efficient way of dealing with concretion, apart from the special case of the use of explosives.
Various methods were used to remove the coral lumps that had been broken free from the binding concretion, and the loosely packed coral below this. During rough weather, when the workboat could not be positioned over the site, thecoralwasbaggedandman-handledoffthesite.Thefull sacks weighed about 50 kg (in water), and were piled, 10 m away to either side and well clear of the site. In good weather, these sacks were raised with the workboat winch using an 'octopus' system: twenty or thirty light lines were attachedtotheshackleontheendofthewire.Thiswasthen dropped onto the site, and the sacks attached to the lines with quick release knots. The whole was then raised be- hind the boat, and the vessel manoeuvred, underpowerbut still attached to the mooring, so that the vessel was off the site. Thequickreleaseknots were then pulled and the sacks dumped. For large coral lumps, a steel-mesh lifting tray 3 x 1.2xO.8 m was constructed (Fig. 14). This was left on the site to be filled by the divers; the boat was then brought in and the tray lifted by a four-point strop attached to the corners of the tray. A similar strop, attached to the lower partofthetray,wastiedtotheboat,afterthetraywaslifted. The vessel was then steered off the site and the tray lowered, putting the strain on the lower strop. As a result the tray tipped upside down, dumping its load. With this system, it was possible to dump 1.5 tonnes per load, the whole operation taking a few minutes. Using these meth- ods,about150cubicmetresofcoralwasremovedfromthe site during the four seasons.
The soft sandstone building blocks were raised using rope strops and the boat winch, using the hydraulic A- frame to swing the blocks on-board. This type ofoperation could be carried out only in relatively good weather conditions, as the boat had to be dropped back from the mooring so that it was over the site and the vessel needed to be reasonably stable to prevent the blocks being dam- aged when lifted on-board. A maximum of about 1.5
tonnesofblockscouldbeloadedontothevesselatonetime for transport to the Beacon Islandfield station. Initially, the unloading from the vessel onto the jetty created some problems. These were partially resolved by the construc- tion of a davit on the end of the jeuy. Then, a half-tonne capacity trolley was made to run the blocks ashore along the cat-walk, and a portable sheerlegs (Fig. 6) was used to unload them from the trolley. A total of 128 blocks
weighing 27 tonnes were recovered, transported to the island, and unloaded in twelve days.
Eight cannon wcre recovered from the site. Initially, cannon were raised with 200 kg-capacity lifting balloons. These balloons were tied to the cannon, filled with air until the cannon floated and then towed back to the island. Later when the lifting capacity of the boat winch was increased, the cannon were raised behind the boat (in some cases loaded on-board) and then motored back to the island. Great care was required in handling the iron cannon so as not to damage the protective concretion covering the gun. Ifthiswerebroken,thesoftgraphitizedsurfaceofthegun was exposed, and the markings and mouldings could be easily and irreparably damaged. The best system devised to protect this concretion during lifting was to use 100 m diameter hawsers, racked and seized into a figure-of-eight strop. The cannon was supported by two of these strops which were chained together, above the gun, and onto the lifting wire, thus providing a soft support for the gun.
Large concretions were raised in a cargo net and brought back to the field station for examination and extraction of artefacts.
During the timber-raising operations, flat planks were loaded into the tray used for raising coral. When this was full, the whole was lashed down and the tray raised onto the workboat, for the brief trip back to Beacon Island. Large, curved ribs that would not fit into the lifting tray, were stropped using flat material straps to prevent chafing or scoring of the soft timber surface. The timbers were usually hauled onto the workboat by hand.
To remove sand, gravel and small coral spoil, two types of airlifts were used. One was a continuous 10 m length of Helil1ex reinforced plastic tubing, 120 mm in diameter. A securing point was located about 3 m from the working end, and this was attached to a small concrete sinker about 20 kg in weight. The discharge end was tied off so that the spoil was deposited about halfway up the site towards the reef.Itwasfoundthatthisspoilwasthendrivenoffthesite and over the reef by the surge. Air was fed to the airlift via a 30 mm supply pipe which was run up the working end of the airlift and securely attached to it. The other airlift was arigidP.V.C.pipe,5mlongand150mmindiameter,with a further 4 m of Heliflex tubing attached to the working end. The airlift was anchored at the junction of the two pipes, and the air supply and discharge were arranged in the same way as the flexible airlift. The air supply was emulsified to improve efficiency, and under normal oper- ating conditions, with a 2500 litres per minute air supply, it was possible to run both units and remove material up to slightly less than the diameter of the airlift tube.
Problems were experienced with spoil blocking the airlift pipe at some distance up the pipe. This was often a result of an operator allowing a large object to enter the airlift, which, turning in the pipe, then jammed it. To prevent this, a restriction was made in the mouth of the airlift The airlifts were found to be reasonably manage- able, even in strong surge conditions and, provided that they were securely anchored, they could be left on the wrecksitethroughouttheseason. Attheendoftheworking day, the air supply pipes were disconnected and brought on-board the workboat
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