would reduce the cost still more and could yield a better product. If 
the treated concrete is spread 0.5-inch thick over standard concrete (as 
it might be in an OTEC application) the toxicant cost is $1.64/ft? if 8% 
of the concrete weight is TBTO/creosote. 
The set of specimens prepared using methoxychlor/TPTH/Cu,0 appears 
to possess good antifouling properties. At the concentrations used, the 
cost of toxicants in this set is $63.40/ft?. This amounts to $2.64/f£t2 
when applied at a 0.5-inch thickness. 
Two sets of cylinders were evaluated where a coating was placed on 
otherwise untreated concrete. Both seem effective as antifoulants. The 
first of these is a brush-applied organotin polymer which would, at the 
level employed in this experiment, cost $0.10/ft2. It should be able to 
be applied in a heavier coating, perhaps by repetitive applications 
The second is a proprietary organotin-impregnated elastomer (Nofoul 
rubber). The cost of the materials and adhesives in this system is 
$4.85/ft*. A thickness of 0.08 inch is assumed. The manufacturer 
produces sheets having greater thicknesses at higher costs. 
Ocean Site Effects 
Differences in the rate of attachment and growth of fouling organisms 
at the two sites were expected. Figures 2 through 6 show these differ- 
ences. As a general rule, the first members of the fouling community 
observed on specimens at Key Biscayne were algae. Barnacles soon followed, 
eventually covering the specimen completely. At Port Hueneme, the 
sequence of attachment of fouling organisms was slower so that many 
different organisms would be found at one time on specimens where there 
was attachment. 
Each time a set of treated specimens was exposed, a set of controls 
was exposed with it. The importance of this cannot be overstated. For 
example, the number of larvae of barnacles in seawater varies tremen- 
dously at different times throughout the year and reaches maxima at 
different times in different years (Ref 2, Chap. 5). Similarly, one is 
cautioned not to compare weight increases of specimens exposed at one 
site versus those exposed at another. The only way an evaluation of the 
effectiveness of a given toxicant can be made is by comparing the weight 
increase of specimens prepared with it versus those of control specimens 
exposed at the same time in the same place. 
Objective Ratings 
Table 3 shows one subjective rating made on the first batch of 
specimens, and the final objective rating made on the same specimens. 
The objective gravimetric method yields a more easily handled numerical 
rating that can readily be plotted (Figures 2 through 6). Further, 
different people using this method will arrive at the same figure. 
Subjective rating is highly dependent upon the rater's judgment, 
which varies from person to person and from day to day. For these 
reasons, the objective weighing method of evaluation was employed in 
this experiment. No major differences in types of fouling have been 
noted between treated specimens and untreated controls — only amounts. 
11 
