Moorings and Diving
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Moorings
A four-point mooring system was installed in 1994, providing a means to secure the expedition support vessel over the site in a fixed position. Having the mother vessel TSMV Pacific Conquest securely moored directly overhead was a critical factor for effective and safe use of Surface Supply Breathing (SSB) equipment. Each mooring point comprised a 750 kg Danforth anchor, approximately 55 metres of 20 mm stud link chain and a one tonne dumper block.
The 1998 expedition saw excavations continue in the stern section with additional excavations being conducted in the bow section. These were carried out at the same time by two teams diving simultaneously.
The mooring system was adjusted and improved by Michael St James, the skipper of the Pacific Conquest, by the addition of a fifth mooring point. The team working in the bow of the wreck dived from the mother vessel's stern, while the team working in the stern of the wreck were deployed amidships.
Diving
From the 1993 expedition onwards, all divers were trained in the use of Surface Supplied Breathing (SSB) equipment. This was the preferred diving equipment as it enabled excavators to spend longer times on the seabed than possible with SCUBA.
During the 1980s, museum excavators had only used SCUBA gear. This had limited the length of time divers were able to stay underwater, either because of a limited air supply or because most recommended dive tables indicated (non-decompression) dive limits not exceeding 17 minutes. Depending on the diver, the maximum depth (36 m) and whether heavy or light work was being performed, effective dive time on SCUBA was only 11 to 17 minutes per dive.
With SSB gear, however, as long as air was pumped to them, divers were able to stay underwater longer. Theoretically, they could be submerged for hours, however, this never happened as eventually the divers would get too cold (even in tropical waters) and, more importantly, would be exposed to another complicating (physiological) factor associated with diving on air: decompression sickness-or the "bends" as it is commonly known.
At the Pandora wreck, a typical SSB dive profile using the Canadian DCIEM Decompression Tables, allowed 45 minutes of "bottom time" and a two minute ascent from the seabed to a decompression stage ('deco stop'), rigged at exactly 9 metres depth under the hull of the mother vessel. Here, divers subsequently decompressed for 30 minutes breathing 100% oxygen; lastly there was a one minute ascent from 9 metres to the surface.
This 78 minute dive was performed once a day by each diver. However, after six consecutive days of diving, every diver was rostered off for one day of so-called "nitrogen de-gassing"-as an added safety precaution against "bending" the divers.
On the dive deck
Although SSB equipment delivered safer, more effective and cost efficient diving operations, it did mean that more equipment had to be taken onboard to support the diving operation. One item of absolute necessity was a recompression chamber (RCC) with all of its auxiliary plant (such as liquid oxygen tanks and compressors).
This had to be kept on the dive deck in case of emergencies, when immediate access to the RCC would be required. Hence the need for a large, uncluttered work deck capable of accommodating the chamber, as well as the rest of the gear needed to stage two SSB dive teams (four divers) simultaneously.
Along with all the other equipment to be taken-such as the pumps to operate two water dredges, the small three metre inflatable boats as tenders, fuel, liquid oxygen tanks and cylinders, tools, a portable field laboratory for on-deck conservation, artefact registration and artefact processing-it is obvious why a large mother vessel like the Pacific Conquest was required. The expeditions required a vessel capable of carrying equipment to support an expedition team of up to 45 people.