Timbers wreck

Loose timbers that were swept away from this wreck soon after exposure in 1984 were attacked by gribble and in 12 months all surface detail was lost. After 24 months exposed loose timbers had lost 50% of their bulk and were virtually unrecognisable (see Figure 4). 

The natural degradation of wooden shipwrecks in-situ can be slowed down, or even eliminated, by covering the site with a physical barrier such as polyethylene or polypropylene textile (Figure 15). This method is very effective because it uses the wrecked environment to create an overlying mound of sediment, which becomes part of the site. It also physically prevents colonisation of any subsequently exposed wreck timbers by wood-boring animals, like shipworm. 

It has recently become evident that bacteria cause most of the microbial degradation of timber in sunken ships. Mouzouras et al. 118) describe various forms of bacterial attack that were observed in timber from the Mary Rose. The attack includes tunneling as well as erosion forms. Soft rot was also observed. Kim 105) reported that timber from a wrecked Chinese ship that had been submerged for over 700 years was degraded by soft rot and bacteria. Studies of timber from the Swedish battleship Kronan, which sank in the Baltic Sea in 1676, show that most of the microbial degradation of both oak and pine timber can be attributed to erosion bacteria. Soft rot and attack by tunneling bacteria occurred to a much lesser extent. 

The appearance of the timber in the dried wooden vessel is not perfect, and some longitudinal and transverse cracking has appeared. This result raises the question of the need for pretreatment to alleviate the considerable stresses involved in direct freeze-drying of degraded wet wood. The system used to treat the Marseille wreck was nevertheless conceived on an imaginative scale and deserves further research and development, particularly with respect to appropriate pretreatment. 

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