|
The expedition vessel was to be The Sulu Venture. This vessel was withdrawn by its owners at the last minute and, as no ships were available out of the Philippines, DSD hired a vessel out of Singapore. This change of mobilization locale forced an extended logistics and customs exercise through Singapore, and hence the expedition was two days late to the site.
The operation was conducted from the Pacific Beaver, a 150 foot oil field support vessel chartered from Swire Offshore Services of Singapore. Once on site, the first task was to moor the vessel directly over the site. In order to minimize the environmental impact of mooring the vessel to the reef, permanent moorings were drilled and cemented on the top of the reef such that they formed a 90 degree stern bridal when the vessel was positioned over the site. The Pacific Beaver was equipped with a bow thruster which was used (instead of a single deep water mooring) to steady the vessel against its stern bridal. By adjusting the lengths of the legs of the bridal, the position of the ship over the site could be adjusted. The reef mooring system exceeded expectations in the extreme weather conditions, (see below) allowing the vessel to remain on its mooring in 30 knots of (beam) wind. Accurate positioning of the ship over a selected site proved possible with this method in up to 18 knots beam winds.
DSD shipped out twenty tons of equipment directly to Singapore for installation aboard the Pacific Beaver. This equipment included a DHD2 ROV (to be used for surveys),a Phantom Ultimate ROV (to be used for excavation work), both built by deep Ocean Engineering Inc., high quality video cameras, stills camera, 5-function manipulator, experimental artifact suction tool, an advanced sub-sea acoustic positioning system, a dual-layer, multi-basket artifact lift and a suction dredge. Winches, a crane, spare parts and cables were also sent. Most of the equipment was shipped in two 20 foot containers, one of which was fitted as sub- sea control center.
From the second day on site, the weather deteriorated (unseasonably early), producing squalls and gale force winds and subsequent ground swells on the port beam. The strongest gust measured was forty knots, and the winds were frequently above 30 knots. Beam winds above 25 knots over- powered the ships bow thruster, forcing the main engines and screws into play in order to keep the ship off the reef. Under these conditions, station-holding was abandoned and sub-sea operations were not possible. Future expeditions should be undertaken earlier in the season to avoid similarly experiencing an early start to the south west monsoon.
Deck launch and recovery of the heavy equipment, together with the need to put a man in the water for recovery of the ROV, proved the limiting factor for safety considerations when the ship roll exceeded approximately plus and minus 10 degrees. The combination of the above factors, together with the added strain of needing all hands on deck during launch and recovery, reduced the effective bottom working time of the expedition by more than 50%. (Note: the hazards of quickly-developing squalls and unstable sea conditions were judged too hazardous for night-time operations, however on two dives the ROV remained sub-sea for periods of 20 hours). The expedition achieved the sub-sea working time it did due to the dedicated efforts of the expedition team and the captain and officers of the Pacific Beaver.
The acoustic positioning system failed to function, hence thirteen half meter measuring sticks and four (lead) marked position reference points were placed on the site. The reference points will allow accurate position survey to be undertaken in the future (and, for this expedition, the reference points were surveyed with the ROV using a traditional series of magnetic compass bearings). A computerized (CAD) map of the site was produced using these results, together with preliminary distance estimates from photo analyses.
Two trenches were excavated to reveal bottom structural timbers of the Royal Captain. This showed the tumulus to be relatively shallow, and containing a considerable quantity of good quality porcelain of private trade. All artifacts revealed in this process were documented, mapped, photographed and set aside in padded containers for later recovery to the surface.
The artifact suction tool was successful, enabling the ROV to easily "pick up" and place the artifacts in their chosen basket compartments (none were broken in this process) . However because of the weather conditions, launch and recovery of the artifact lift proved very difficult. On the first launch (with no artifacts in the lift), the ship lost station in a squall and the lift was severely damaged against the reef wall, permanently disabling the main suction dredge. The lift was partially repaired, enabling the team to risk one single cycle that successfully recovered a total of 54 artifacts (from the trench). The recovered artifacts included samples of tumulus materials for analysis and a number of intact porcelain items, which were treated and by the museum staff and are in an excellent state of preservation.
Since the company trade (a large bulk of porcelain) was not found on the tumulus, a wide area search of the debris field was undertaken. The debris field was re-surveyed, and many interesting items were found. Most of the ship's cannons were accounted for and the ship's bell was found at 363 meters, however, pending further study of the high quality video tapes, the company trade (porcelain) was not found.
All ROV dives were recorded in dive logs. The recovery of several artifacts enabled the documentation methods to be tested; traditional means of hand documentation were employed in parallel with computerized bar coding.
Documentation of the tumulus was undertaken primarily by a dedicated high quality video camera system with a local recording (12 hours total of tape ) for security, and redundancy 100% coverage of all ROV activities were recorded on the surface (60 hours total of tape) . Reconstruction of the tumulus will be undertaken from the sub-sea high quality tapes, using advanced software to scale and blend multiple images. Hence, the results of the important archival phase of the expedition and the methods proposed will be published and available to the Museum authorities by August 1996.
Overall, while there were numerous detailed successes and failures of the technology and tools and methods, as always, there were lessons learned. The preliminary conclusions from the expedition are that a full scale robotic archeological excavation of the Royal Captain is eminently practical, and proving that the company trade is not subsequently located (which would increase both the work load and the value) the known tumulus can be readily excavated in one season with budgets of perhaps half of that originally planned.
Back to top
|
