236 BULLETIN OF THE BUREAU OF FISHERIES 



The report of the American Society for Testing Materials, subcommittee No. 23 

 (1925), records the results with 11 vessels partially or completely covered with test 

 paints, and in addition to these 7 have been examined in the course of this investigation. 



From the data given in their report it can be seen that in most cases there was no 

 noticeable difference in amount of fouling, although in almost every case the experi- 

 mental paint film did not "hold up" as well as the "standard." These data indicate 

 not only the ineffectiveness of poisons but also the very significant effect of the nature 

 of the surface film in the matter of fouling, a subject that wiU be considered next. 



SURFACE FILMS 



Since the major importance of the problem of fouling of ships' bottoms centers 

 about the question of frictional resistance of the surface of the ship in passing through 

 the water, the nature of the film covering this surface is of prime importance. It 

 has been recommended by many people that paints of a greasy character would be 

 advantageous, on the theory that there is no adhesion between the films of oU and 

 of water. However, McEntee (1915) maintains, from his experimental data, that 

 the most favorable coating for ships' bottoms, as far as skin friction is concerned, is 

 a paint that offers a permanent, hard, smooth surface. 



From a biological point of view, as far as the attachment of larval forms causing 

 fouling is concerned, the nature of the surface film also is of great importance. In 

 the course of the examinations considered in this paper it was noted that fouling 

 was most severe in regions where the surface was not smooth. Thus, in the areas 

 where paint had peeled off, as shown in Figiu'e 33 A the growth frequently was 

 heavy, provided corrosion had caused a roughened surface. Frequently the number 

 of barnacles that attached to a colony of Bryozoa (fig. 33 5), or even to other 

 barnacles, would be much larger than on the adjoining smooth surface of the ship's 

 huU. In other cases, where the pigment of the paint had not been mixed properly 

 before applying, the resulting rough surface often was fouled more heavily than in 

 regions where the paint offered a smooth surface. (Figs. 33 C and D.) These 

 observations are confirmed by reference to the report of Adamson (1922), in which 

 he presents data to show that the "problem [of fouling] covers physical properties 

 as well as chemical properties of the paint film." 



In the simimer of 1922 Bray (1923) made some preUminary tests on the effects 

 of various surfaces in relation to the attachment of barnacles. He set out two sets 

 on separate racks at Beaufort, N. C; but, he concludes, "unfortunately, the length 

 of time the racks were exposed, due in part to the lack of material and to an accident 

 which caused them to lose rack A, after nearly four weeks exposure, renders any 

 attempt at anything but tentative conclusions of Httle value." 



These tests included such surfaces as glass, beeswax, eseter gum, and shellac, 

 with various types of poisons and combinations. He, however, concludes that 

 "there seems httle doubt that a fihn of a 'waxy' nature is capable of greater retention 

 of the toxic agent than a thinner, harder film. " This point is brought up at present, 

 without reference to the question of poison, only to show the superior results obtained 

 with "waxy" surfaces. 



The writer has observed barnacles attach to metal surfaces of many sorts, 

 provided no electrolysis was present, to wood, stone, tile, glass, rubber, and shells of 

 more than 30 species of animals — in fact, to everything that is found submerged at 



