In order to verify the efficacy of antifouling paints, static raft tests were conducted using a series of test paints containing cuprous oxide concentrations of various levels from 0% to 40%. The static raft tests were carried out for 90 days at a site in Nagasaki bay in winter with non-aged test plates, and for 28 days at two sites in the Seto Inland Sea in summer, fall and winter with aged test plates. The aged test plates underwent dynamic immersion pre-treatment for 45 days under a seawater flow of 10 knots at 20°C in a dark room to simulate the actual ships’ conditions. The efficacy of antifouling paints was investigated using the relationship between fouling (animals and algae, slime) and the amount of cuprous oxide. After the end of each test, copper leaching rates for the test plates were measured for the test plates at the laboratory to verify the correlation between the fouling (sea animal species, macro algae, and slime) and the test paints containing various levels of cuprous oxide concentrations. The results showed that the degree of fouling decreased as the cuprous oxide content increased. The threshold of cuprous oxide content for macrofouling prevention was identified to be around 20% for sea animal species and around 5% for algae, while all test plates were subject to microfouling by slime.
