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The St Mikael is a demanding diving site. The wreck lies at a depth of approximately 40 metres, which corresponds to the height of an almost 15-floor building. In the waters off the Finnish coast, only a small portion of sunlight reaches all the way to the depth of the St Mikael. Normally, the site of the wreck is so dark that it is necessary to use artificial lighting. Moreover, it is always cold in these depths: the normal temperature ranges from +2 to +4 degrees Centigrade. The fine sediment covering the wreck further impairs the diving work. When agitated, the sediment blurs all visibility very easily. This is why the conditions call for experienced divers and advanced equipment. Preliminary preparations and safety measures need to be thorough. In addition to the safety of divers, the team has to make sure that the archaeological finds or the wreck structures are not damaged during the work carried out.
The depth at which the wreck lies and poor visibility are the biggest obstacles to the research of the St Mikael. The depth has an impact on the working time of the divers. This is calculated by means of diving tables, which have been drawn up to prevent the decompression sickness or the bends, which at worst may lead to death. A diver using compressed air can in practice stay at the wreck for 15 to 20 minutes at a time twice a day.
Natural visibility at the wreck ranges from 20 centimetres to several metres, depending on factors such as wind direction changes, flows, agitation of the soft seabed, presence of algae and the season of the year. Sediment accumulated inside the wreck and on the structures blurs the underwater visibility by the smallest movement. The average thickness of the sediment layer is 30 to 40 centimetres. Over 250 years, the sediment layer has become more than one metre thick in places. There is even more sediment inside the ship.
In conjunction with the diving expeditions arranged in 1997 and 1998, it was also necessary to dive into the partly collapsed interior of the St Mikael. Specific cave diving techniques were used here, meaning that all the primary equipment of the diver was provided with at least one backup system. As an example, if one regulator system had broken, the diver would have been able to use another, completely separate system. The air volume available to the diver is also larger than normal when diving into the wreck.
After the diver has gone inside the wreck, there is only a couple of seconds of time to observe the environment before the agitated sediment completely blocks off all visibility. As the working time down below is limited, the divers cannot wait for the water to clear up again, because this would take hours in the cargo hold and elsewhere inside the ship. A diver who cannot see is faced with risks such as entanglement, and the diver may also accidentally damage valuable archaeological material.
Voluntary divers have made an invaluable contribution to the work carried out on the St Mikael and to Finnish naval archaeology in general. Over the years, dozens of divers from several diving organisations have participated in the field work conducted on the St Mikael. The diving team participating in the work carried out in 1997 and 1998 included knowledge and skills in many different areas. The team had divers with experience in underwater construction, photography, measurements and penetration diving.
© Anna Nurmio-Lahdenmäki 2000