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 folding, 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 tUes were submerged at the Fisheries biological station in a tidal channel, at a 

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

 these experiments, because it had been found that glazed tUes 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.- 



-Nurriber of barnacles that attached daily, one month, on unglazed tiles of different colors 

 at Beaufort, N. C. 



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, 



