The performance of Hem fir (Tsuga heterophylla) and Southern pine (Pinus sp.) treated with ammoniacal copper zinc arsenate (ACZA) and copper dimethyldithio carbamate (CDDC) at two retention levels of each preservative was assessed in tropical marine waters at Krishnapatnam harbour on the east coast of India. Panels treated with ACZA of lower loadings (23.1 Kg/m3) had failed in 38 months while the performance of higher loadings (38.1 Kg/m3) was very effective and lost in 54 months. Panels treated with CDDC of lower loadings (4.31 Kg/m3) was severely attacked by borers and lost in 22 months and higher loadings (10.86 Kg/m3) damaged in 38 months. The results indicate that, ACZA at higher lodgings is very effective in tropical waters and durability enhanced over 13 times compared with untreated controls. Teredinids were important on control panels, while ACZA treatment was damaged mainly by pholads. Nine species of borers were identified on panel including 2 species of pholads and 7 teredinids. The fouling biomass was slightly higher on CDDC treatments than ACZA and barnacles, bryozoans, oysters and serpulids were dominant groups on test panels.

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