Ian D. MacLeod

Shipwrecks and applied electrochemistry

Abstract A study of material recovered from shipwrecks provides a fascinating display of the interplay of temperature, marine growth and oxygen content on the corrosion of metals. Analysis of corrosion products can give information about the changes in site conditions as corrosion mechanisms are sensitive to changes in chloride and sulphide ion activities. Access to metal artifacts which have been exposed to a marine environment for centuries may provide the only valid results for long term exposure tests.

Corrosion and conservation management of iron shipwrecks in Chuuk Lagoon, Federated States of Micronesia

Abstract A series of in situ corrosion measurements on World War II Japanese merchant and military vessels sunk in Chuuk (Truk) Lagoon in 1944 was conducted in 2002 as part of a study of the cultural heritage values of the wreck sites. The data provide evidence of episodic loss of the protective layer of marine concretion, which directly increases corrosion of the underlying metal and removal of the archival microenvironment record. It is likely that dynamite ‘fishing’ is the most likely cause of such losses. All the vessels, apart from the Fujikawa Maru, showed a corrosion mechanism that is common to historic iron shipwrecks. The apparent sensitivity of the corrosion potentials and the pH of the corroding interfaces to water depth have been interpreted in terms of the overall amount of water movement and the aspect or orientation of the wrecks with regard to being horizontal, upside down or inclined. Corrosion rate equations predict that many of the wrecks in Chuuk Lagoon will retain their existing integrity for the next ten to fifteen years before undergoing significant collapse. The corrosion rates in Chuuk Lagoon were between 26%and 30% lower than the iron shipwrecks at the same depth in open-ocean waters.

In Situ Corrosion Measurements and Management of Shipwreck Sites

The overall impression of an iron shipwreck site is often dominated by the remains of the boiler, engine, and frames that once gave the vessel its form. In warm tropical to subtropical seawater, corroding iron and steel rapidly become encapsulated by encrusting organisms such as coralline algae and bryozoa (North, 1976). This encapsulation begins the process of separating the anodic and cathodic sites of the corrosion cell, with oxygen reduction generally happening on the outer surface and oxidation of the metal occurring underneath the marine growth (MacLeod, 1989a). Under such conditions, the cathodic reduction of dissolved oxygen is the rate-determining step in the overall corrosion process.

In situ conservation surveys of iron shipwrecks in Chuuk Lagoon and the impact of human intervention

Abstract Regular site inspections are an integral part of the overall management strategy for a submerged site. The primary focus of an on-site corrosion survey is to collect as much pertinent information as possible to assist in ascertaining the extent of deterioration and structural integrity of a site. Further inspections are then required at regular intervals so any changes in the integrity of the site are noted by direct comparison with earlier surveys. The more surveys carried out, the better, as they will provide more information regarding the rate of deterioration and the inherent stability of a site, which will assist in recognising which sites are a priority for future implementation of appropriate in-situ conservation management strategies. Hence, as an example, over a five-year period, a series of in situ conservation surveys were performed on a selected number of World War II Japanese wrecks located in Chuuk (Truk) Lagoon, in the Federated States of Micronesia. During World War II, the Japanese established their principal military naval base at Chuuk (Truk) Lagoon but in February 1944, American forces attacked the base and consequently, many of their ships were sunk and a number of aircraft were lost in the lagoon. These wreck sites have become very popular dive sites and therefore, Chuuk Lagoon has become one of the major recreational dive destinations in the world. As unsustainable fishing practices have become more prevalent in this area and with the downturn in the tourism industry due to the global economic crisis, it is very important to monitor the archaeological, biological and structural integrity of the wrecks in Chuuk Lagoon, so early intervention may prevent loss of these internationally significant underwater cultural and natural heritage sites, which are intrinsically linked to the economic future of the local Chuukese people.

Rock art conservation and management: the past, present and future options

Abstract The primary function of this review is to provide the reader with an overview of the issues that impinge on the conservation management of rock art sites around the world. Because of the author’s familiarity with Australian rock art sites, particularly those in the Kimberley region of Western Australia, the review is somewhat slanted towards Australian issues. The first section covers factors associated with the basic points of documentation, which includes the sites themselves as well as the images painted or engraved on the rock surfaces. Techniques range from the rudimentary methods of sketching and tracing to the use of photogrammetric, photographic, videographic and colourimetric methods of documenting both the nature of the surfaces and the way in which the images have been presented. The involvement of indigenous persons in all the areas of documentation and any subsequent intervention at the site or on the images is considered to be most important. Detailed discussion of the role of controlling visitor access indicates that this is a primary factor influencing the deterioration of rock art sites, whether they are in subterranean environments or in open shelters. Management of the natural factors of the impact of flora and fauna and human visitation at the sites are discussed and some simple and practical options for cost-effective management are provided. The importance of recording base-line information about the microclimate, in terms of the temperature and relative humidity, are frequently stressed. The roles of bacteria, lichens and moulds are reported, with some guidance as to how the relative importance of these forces of decay varies with the nature of the site. The next section contains a detailed discussion regarding the nature of the pigments that have been used in the execution of the paintings and how these minerals and other products have undergone changes. Not all natural ageing processes lead to the irreversible deterioration of the images. Examples of beneficial weathering are given as illustrations of the need to identify carefully the nature of the materials on the surface, in the substrate and in the immediate microenvironment before reaching any decisions as to the nature of the site. The impact of graffiti and the removal of the same is reviewed in the context of overall visitor and site management. The final section covers the primary role of water as the principal agent of decay of the painted surfaces. This can be in the form of direct dissolution of the rock substrate, erosion, salt efflorescence and the promotion of bacterial and algal activity. The concluding chapter offers some comments on the future directions in the management of rock art sites and the need for continuing research.

Managing a Monitor — the Case of HMVS Cerberus in Port Phillip Bay: Integration of Corrosion Measurements with Site Management Strategies

Abstract The hull of the former HMVS Cerberus (1926) collapsed two metres during gales in December 1993, leaving the vessel half-submerged. Sunk as a breakwater in 1926, the vessel is one of the few remaining and accessible twin-turret Monitor-style warships from the 1870s. This paper presents the complex history of attempts to stabilize the site and to preserve the wreck. A series of in situ corrosion studies of corrosion potentials, pH, and residual metal thickness have provided a special insight into the processes of decay and have paved the way for future site stabilization. Removal of the four 16-tonne 10 inch Armstrong rifled muzzle loading guns and their in situ treatment alongside the wreck have assisted in relieving some of the stress on the remaining structure. The paper reports on correlations between the corrosion rate and the formation of concretions and how to determine the end point of an in situ treatment for cannon.

Effects of water vapour and rock substrates on the microclimates of painted rock art surfaces and their impact on the preservation of the images

Abstract Microclimate data from typical sandstone and limestone rock art sites in the west Kimberley region of Western Australia were recorded in both the wet and the dry seasons. The research described in this paper shows that the climatic behaviour in rock shelters is more amenable to direct interpretation when the relative humidity at any given temperature is converted to absolute humidity or water vapour pressure. It has been shown that many of the sites act as ‘closed systems’ with little input or output of moisture until water bearing fronts or drying winds change the local microenvironment. The rate of cooling of points within the shelters is largely determined by exposure to the sky, which facilitates cooling by emission of long wave radiation and by the heat capacity of the moisture in the air. It was found that the heating and cooling rates for limestone sites in the Napier Ranges are more sensitive to changes in moisture than the sandstone sites in the Mitchell Plateau. The survival of painted images on the rock surfaces is directly linked to the way in which the substrates respond to changes in the moisture content of the sites.

In-situ Corrosion Measurements of WWII Shipwrecks in Chuuk Lagoon, Quantification of Decay Mechanisms and Rates of Deterioration

This paper is based on a series of measurements taken on WWII historic shipwrecks that resulted from the effects of Operation Hailstone in February 1944 on the Japanese merchant fleet which was assembled in Chuuk lagoon, Federated States of Micronesia. More than 65 shipwrecks and 250 aircraft were sunk during two main bombing raids. The vessels lost covered a wide range of underwater orientation and water depths and so provided a perfect suite of corrosion experiments. Since the fuel on board the aircraft was either readily burnt at the time or was lost through volatilisation, the wrecked planes present no pollution problems today. However the bunker fuel kept inside on-board storage tanks does present a real conservation management crisis. In-situ measurements on many vessels have determined how water depth, the localised wreck topography, dissolved oxygen levels, temperature and salinity affects the corrosion rate of cast iron and mild steel. Thus corrosion rates can be calculated with confidence.

The Australian Historic Shipwreck Preservation Project: In situ Preservation and Long-Term Monitoring of the Clarence (1850) and James Matthews (1841) Shipwreck Sites

Increasingly, archaeologists are opting for on-site examination, reinterment, and in situ preservation of underwater cultural heritage sites as the first option in the management of sites at risk, as opposed to the more traditional excavation, recovery, conservation, and display/storage methods. This decision will inevitably be based on significance assessment, degree of perceived risk, and resourcing issues. However, long-term monitoring must become an integral part of these management programmes in order to quantitatively evaluate the effectiveness of the in situ preservation techniques employed. In 2012 the Australian Historic Shipwreck Preservation Project (AHSPP) was awarded a large Australian Research Council (ARC) Linkage Grant, enabling ten partner organizations and three Australian universities to collaborate in one of the largest multi-organizational maritime archaeology projects to be undertaken in Australia to date. One of the major aims of the project is to develop a protocol for the excavation, detailed recording and reburial of significant shipwrecks under threat, fostering a strategic national approach for the management of underwater cultural heritage (UCH) sites at risk. Two historically significant shipwreck sites that are considered under threat were chosen for this longitudinal comparative study — the Clarence (1850) located in Port Phillip Bay, Victoria; and the James Matthews (1841) which lies in Cockburn Sound, Western Australia. Both sites have been preserved in situ using two very different but innovative remediation strategies. More importantly, long-term monitoring programmes have been implemented on both sites, which will characterize changes in the reburial environment and the effect on the reinterred materials. In this way, the efficacy of both in situ preservation techniques will be systematically tested, providing a comparative analysis of practical protocols for the long-term protection and management of underwater cultural heritage.

The effects of storms and diving activities on the corrosion rate across the SS Yongala (1911) site in the Great Barrier Reef

Abstract The initial assessment of the condition of the wreck of the SS Yongala (1911) took place in 2005 and was followed with additional in-situ measurements on three field trips in 2007. Analysis of the corrosion potential, pH and plate perforation data confirmed that the superstructure, deck and hull plates are highly corroded and that the most extensive corrosion is on the port side gunwale. The high corrosion rates found at the forward end hull/forecastle deck level and at the stern near the rudder are consistent with the exposed locations which lie proud of the seabed and are subject to significant water movement across the site. Comparison of the original structure and its present condition with site records from previous visits suggest that the wreck is following the Riley waterline theory with the port side frames eventually collapsing and the bow and or stern section breaking off from the vessel. This collapse could happen at or near hold 3 and or around holds 1 and 2. Currently the bow is corroding at a higher rate than the stern end. Changes in the souring of the site and past practices of tying up to the wreck have been significant factors in accelerating the corrosion of this historically significant iron shipwreck.