The attachment af the macroscopic or visible 

 fouling forms starts the critical stage of foul- 

 ing. The effectiveness of an antifouling paint 

 must be measured by its ability to hinder the at- 

 tachment of these organisms, since, vhen once 

 attached, they seem to grow regardless of the 

 toxicity of the paint. 



All of the important macroscopic forms begin 

 as tiny, microscopic forms, called larvae. For a 

 short time these larvae swim freely in the water. 

 Then, after a period which varies from a few min- 

 utes to several weeks, depending upon the kind of 

 organisms, they must become attached to a surface 

 in order to survive. After their attachment, the 

 larvae change to the adult shape, and grow very 

 rapidly. The poisons in the paint seem to have 

 little or no effect on the adult organisms. 



An effective antifouling paint must therefore 

 prevent the attachment of the fouling organisms. 



FACTORS AFFECTING FOULING 



Numerous factors influence the amount of foul- 

 ing on a ship's bottom. Ships in tropical and 

 sub— tropical waters foul more rapidly than those 

 in northern, colder waters. In southern waters 

 fouling takes place all year round. In northern 

 waters very little fouling occurs during the win- 

 ter, but in summer the amount may be heavy. The 

 amount of fouling depends to a great extent on 

 the history of the ship since the last docking. 

 Fouling is always heavier in harbors than in the 

 open ocean. Furthermore, some of the younger and 



