Wood resistance against marine borer was intensively studied in the 1940s in Japan, but the research activities on the subject diminished afterward, as the use of wooden marine structures and ships decreased. Today, however, use of wood as a construction material is officially promoted for its environmental benefits. The author started to immerse some wood materials in the seawater pool at PARI (Port and Airport Research Institute) and has continued to study marine borer resistance of various wood materials in the last two decades. In this paper some of the results of those studies are described. Untreated wood samples of various species were immersed in the seawater and the shipworm (Teredo navalis) and gribble (Limnoria sp.) feeding damage was evaluated by the dry mass reduction rates and the observation of the cross sections of the samples. Although some species of wood showed relatively high resistance against the marine borers, no undamaged wood species has been found so far. Wood samples modified by impregnation of low molecular phenolic resin were immersed, and they remained after 15 years of immersion, while some parts of them were severely attacked by gribbles. Thermally treated samples have been in the seawater for 13 years, and only the samples processed at 237.5°C for 5 hours remained without damage by marine borers. The effects of wrapping of wood against marine borers were also studied. The wood samples wrapped with polyethylene mesh with nominal opening sizes of 0.224mm or less were not attacked by shipworms as of 16 months of immersion. The bending rigidities of the wood samples glued carbon fiber sheets with epoxy resin maintained 50% or more of the initial values after 15 years of immersion.

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