The weight loss of exposed timbers was obtained by subtracting the weight of the exposed timbers 

 from the average weight of 15 sections obtained from the three replicate "blank" timbers. In addition, 

 since the dimensions of the timbers and the thicknesses of the sections varied from year to year, all weights 

 were converted to a standard density unit, grams per cubic centimeter (g/cm ). 



In this report, the wood-losses for Douglas Fir and Red Oak were based on direct weighings. Direct 

 weights of chemically treated timbers would have been biased by the calcium carbonate tubes of shipworms, 

 as these timbers were not acid-soaked. Therefore, wood-losses for chemically treated woods were based 

 on radiographic estimates. 



RESULTS 



There was considerable variability in the dimensions and quality of the planks used in this study. Of 

 all the planks used, the Douglas Fir plank in 1983 and the creosote plank in 1984 were most dissimilar 

 in their general dimensions. The quality of the pressure treated woods used in 1984 was poor. The 

 creosote treated plank did not have 20 lbs of creosote per cubic foot because the density of these timbers 

 (g/cm^) was 39% lower than those in 1985. Similarly, the CCA treated sections in 1984 were dissimilar 

 to those in 1985. Weight data are not available for unexposed pressure treated timbers in 1983. To 

 account for all this variability, weight loss extimates were converted into grams per cubic centimeter (g/cm ) 

 of wood (Table 8). 



The correlation between the wood-loss estimates by weight to that by visual inspection of radiographs 

 was highly significant (p > 0.001). The second order polynomial equation used in the regression analysis 

 has an R^ of 0.81 (Fig. 12). The shape of this regression line relative to the data indicates that we 

 consistently overestimated wood-loss using the radiographic method. 



Wood-loss for Douglas Fir and Red Oak are presented in Figure 13. Douglas Fir lost an average of 

 3 times more wood during a one year exposure than did the Red Oak, ranging from 30-70% loss vs. 

 5-55% loss. In general, timbers that lost 70% of their weight were so fragile that several severely degraded 

 timbers were lost from lobster pots. 



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