248 BULLETIN OF THE BUREAU OF FISHERIES 



foul within 30 days from the time of paiatiiig with an antifouling composition. This 

 would indicate the relative ineffectiveness of such material after a very short period. 

 Much more important is the nature of the surface film in its relation to the method 

 used for attaching the larva of the organisms that cause fouling. The beneficial 

 effects of the paints now used very probably can be attributed far more to the nature 

 of the surface (when in water) than to any peculiarly poisonous property that they 

 may possess. It seems probable that undue emphasis has been placed upon the use 

 of poisons in paiats on steel ships, which is probably a hold over from their use on 

 wooden vessels, and that the proper nature of the surface film is the desired goal. 



Finally, this report presents data that demonstrate clearly the relation between 

 light and the attachment of fouling organisms. The experiments with submerged 

 panels of different colors, with submerged colored tiles, and with the cyprid larvae 

 exposed to equal energies of spectral colors, all show that barnacles are more sensitive 

 to Ught colors than to dark, and that at the time of attachment they react away 

 from this stimulus. Inasmuch as red is optically almost as dark as black, it is evi- 

 dent that a worse color could hardly have been selected. Yet red and brown are the 

 colors of more than 90 per cent of the commercial antifouling paints used for steel 

 ships. It is admitted that the red iron oxide so universally used makes an ideally 

 inert "body" for such paints, but if a substance of a lighter color could be found as 

 an adequate substitute, it seems very probable that its use would be advantageous. 



SUMMARY 



1. The fouling foimd on ships' bottoms is composed of both plant and animal 

 organisms, with the latter the more important group wherever fouling is at aU 

 extensive. 



2. Barnacles, hydroids, algae, timicates, Bryozoa, mullusks, and Protozoa are 

 aU found abundantly and in frequency and abundance usually in the order named. 



3. Fouliag organisms are almost exclusively those commonly found on rocks 

 and other submerged structures near shore, especially in harbors. 



4. Fouling occurs almost entirely while vessels are in port. 



5. Passenger ships with regular schedules that permit them to remain for only 

 very brief periods in port are the least foul of any group of vessels. 



6. Most ships are moderately fouled after six to eight months from the date 

 of dry docking. 



7. Heavily fouled ships frequently carry more than 100 tons of fouling materials 

 and occasionally more than 300 tons. 



8. It is conservatively estimated that the annual cost of fouling to the shipping 

 industry of our country is in excess of $100,000,000 per year. 



9. Under optimum conditions vessels foul within 30 days of the time of dry 

 docking and the application of poisonous antifouliag paints, indicating the hypo- 

 thetical value of antifouling paints. 



10. The time that elapses between dry-docking periods is of great significance, 

 but the use made of this time, whether in cruising or in port, is of even greater im- 

 portance, for fouling is proportionally more severe as the length of time since pre- 

 vious dry docking is increased, but it is decreasingiy heavy in proportion to the 

 time spent cruising. 



