Conserv Management Archaeol Sites 4 (2)

Article on the submarine Resurgam, the world's first mechanically powered submarine, built in 1879, lost in 1880 off the north coast of Wales, and discovered 116 years later in 1996. As part of an initial survey the corrosion characteristics and state of preservation of the hull were investigated. The results showed that the hull was actively corroding, although the corrosion mechanism was such that the corrosion products formed were likely to be of a protective nature. The present corrosion rate of the wrought-iron hull of the submarine was hard to quantify based on established means, as the profile of 116 years of corrosion products had not been retained over the entire hull due to spalling of the corrosion products. Where the concretion profile was retained it was possible to calculate an average corrosion rate of 0.1 mm per year. This, coupled with the knowledge of the corrosion rate of freshly exposed wrought iron in sea water, enabled a `worst case' corrosion rate of between 0.1--0.2 mm per hear to be estimated. Two arrays of sacrificial anodes were attached to the hull to test the feasibility of using this method to slow the corrosion rate and stabilise the submarine in situ. Initial rates were encouraging as the corrosion potential was seen to shift to a more cathodic and thus less corrosive potential after their attachment.