FOULING OF SHIPS' BOTTOMS 



243 



It was noticed that the growths were mostly Bryozoa, with a few hydroids, no 

 barnacles attaching at Woods Hole at this season of the year. As the latter forms 

 are of the greatest significance in the matter of fouling, these tiles were used for tests 

 at Beaufort during the following season, where the summer set of barnacles is very 

 heavy. 



Beaufort, N. C. — During the summers of 1924 and 1925 several sets of four or five 

 unglazed tiles were submerged at the Fisheries biological station in a tidal channel, at a 

 uniform distance (about 3 feet) below low water. Unglazed tiles were selected for 

 these experiments, because it had been found that glazed tiles gave conflicting 

 results, because of their "mirror surface" or the reflecting power of such surfaces, 

 as described below. Careful counts of all barnacles that attached, or calculations 

 of the total, based upon accurate counts of several limited areas, were made of all 

 the barnacles attached on each plate during the experiment. These results are 

 given in Table 10. 



Table 10. — Number of barnacles that attached daily, one month, on unglazed tiles of different colors 



at Beaufort, N. C. 



Date, 1925 



Total number attached 



White 



Bufl 



Dark green 



Red 



Black 



June 18 



June 19 



June 20 



June 21.. 



June 22 to 24 



June 25 



June 26 



June 27 1 



June 28— 



June 29 



June 30 



July 1 



July 2 



July 3 



July 4 and 5 i_. 



July 6 



July 7 



July 8 



July 9 



July 10 to 15'. 



July 16 



July 17.. 



July 18 



237 

 520 



712 



570 

 864 

 1, 120 

 1,687 



700 

 672 

 1,032 



2, 068 



128 

 429 



251 

 442 



224 



2,840 

 1,900 

 1, 800 

 1,344 



240 

 584 



720 

 884 

 2, 108 

 2,760 



199 

 961 



1, 164 

 166 

 230 

 750 

 1,400 

 1,800 



1, 757 

 760 

 1,040 

 1, 100 

 2,000 

 1,600 



1,836 

 1,116 

 1,381 

 1,500 

 2,700 

 2,500 



1, 500 

 280 

 263 

 400 



1,900 

 430 



1, 130 

 713 



1, 800 

 500 



1, 200 

 470 



122 

 40 

 53 



212 

 224 

 173 



262 

 300 

 180 



Total, 19 days. 

 Daily average. 



9,864 

 419 



18, 872 

 993 



21, 150 

 1,113 



1,491 

 916 

 1,168 

 1,800 

 3,000 

 1,800 



1, 500 

 564 



1, 500 

 591 



252 



176 



23,914 

 1,259 



1,800 

 944 

 1,900 

 2,200 

 2,500 

 500 



1,700 

 379 

 458 

 520 



300 

 316 

 196 



21,345 

 1, 123 



i Omitted. 



It is evident from this table, which shows the average results of all tests, that 

 the darker the surface the more barnacles are found attached. These results may 

 be seen even more clearly in Figure 36. While a light surface is by no means a 

 cure-all, it will be realized that anything that reduces the fouling 50 per cent is a 

 very important factor. Especially is this true when one realizes that on less than 

 5 per cent of the ships (on the basis of an examination of 250 vessels) may one find 

 a growth of barnacles at all comparable in number to those obtained at Beaufort 

 in less than one week. 



Glazed tiles also were used by the author, but conflicting results were obtained, 

 similar to those recorded in the memorandum report by Perry and Bray of August, 



