Figure 5. Rack of specimens engulfed in fouling after 2-1/2-year 

 exposure near ocean surface. 



Measurements of Water Absorption 



The panels of plastic sheeting were removed from the test racks and 

 cleaned immediately after they were removed from the harbor. The large 

 fouling organisms were removed with a large putty knife, and the panels 

 were scrubbed in seawater with a steel wire scrubbing pad. They were 

 then rinsed in distilled water, wiped with paper towels, and air dried 

 for 10 minutes to remove surface moisture. The panels were weighed to 

 determine the weight of the panels plus the moisture they had absorbed. 

 The panels were stored for 2 weeks in a 37 C drying room to remove the 

 absorbed water from the panels; they were then weighed daily until their 

 weights were constant. The loss in weight from the initial to the final 

 weighing were measures of the moisture absorption of the panels (Table 1) 



Hardness Tests 



Measurements of the hardness of the dried panels of rigid plastic 

 sheeting were conducted by the ASTM method described in Reference 5. A 

 type A durometer was employed for testing the sheets of polyurethane and 

 a type D durometer for all of the others. The average of five readings 

 was used for each measurement (Table 1). 



