For the U.S. Navy, (which has ships having bottom (wetted hull) areas as 

 great as 150,000 square feet) maintaining a fouling-free bottom becomes a 

 major task. In tropical oceans, the Navy has found that ships may begin 

 to experience significant bottom fouling in less than one year if painted 

 with copper-based antifoulant paints as compared to the 5-7 years if 

 painted with tributyltin (TBT) based antifoulant paints. 



The Navy calculates that if the entire fleet (600 ships) were painted with 

 TBT antifoulant paints, the new fuel avoidance costs would exceed $110 

 million annually (calculated with fuel costing approximately $16/barrel) . 



1.1.2 T ypes of Antifoulant Paints . 



Wooden ships have been recorded to have been covered in lead sheets to 

 prevent the action of boring and fouling organisms (as early as 300 BC) . 

 In the 17th and 18th centuries, the use of copper on boat bottoms was 

 found to be more effective to prevent fouling. Cuprous oxide paints were 

 introduced and widely used by the turn of this century. Organ>-mercury 

 compounds and stereoarsenicals were used until the 1970's to increase the 

 biocidal properties of cuprous oxide paints. These compounds are no 

 longer used in antifoulant paints because of their toxicity and 

 environmental contamination problems. 



An antifoulant paint consists of a film-forming material (matrix/binder/ 

 resin/medium) and a pigment. The film-forming material and pigment can 

 affect the following paint properties: strength, flexibility, water 

 absorption, and color. An antifouling paint is similar to any other paint 

 (matrix plus pigment) ; however, the paint film is biocidal due to 

 properties of either pigment or matrix. The antifoulant paint works by 

 releasing small amounts of biocide at the paint surface that kill the 

 settling stages of fouling organisms. 



There are three types of antifoulant paints: (1) conventional or referred 

 to as "free association," in which the biocides are loose in the paint and 

 are released by contact leaching; (2) soluble matrix and ablative; and (3) 

 self-polishing, in which the biocides are added in free association or 

 chemically integrated within a matrix as in the organotin copolymer 

 paints. Types 1 and 2 are referred to as conventional paints; both use 

 the biocide in the free association form. 



Type 1 ("free association") uses contact leaching to release the biocide. 

 In this process, seawater percolates slowly through a tough insoluble 

 paint matrix, see Figure 1.3. The biocides are added in the free 

 association form and are mixed into the paint. They leach exponentially 

 with time. This category of TBT antifoulant coatings has traditionally 

 posed a problem of high early release rate with subsequently shortened 

 time period of protection from attachment and growth of fouling 

 organisms. After a period of less than 2 years, the paint film ages, 

 calcium carbonate (CaC0 3 ) clogs the microchannels in the paint surface 



1-5 



