FOULING OF SHIPS' BOTTOMS 229 



visit to Sante Fe (Argentina), far up on the Salado River, very probably explains the 

 absence of fouling on this route, while vessels that do not visit fresh-water ports 

 usually acquire heavy fouling. Similar explanations would account for the conditions 

 found on the Eastern Pilot (March 25, 1924), the Zaremho (April 11, 1924), and also 

 the Eastern Sword (April 11, 1924). 



The lightship tender Hawthorne (March 10, 1925) was found to be almost clean, 

 in marked contrast to most vessels of her group. The fact that she spent consider- 

 able time in the Connecticut rivers probably explains this condition, on the basis of 

 the effect of fresh water. 



While there can be no doubt that fresh water kills many of the organisms that 

 cause fouling, yet that does not imply in any way the natural conclusion that such 

 ships would then be clean. On the contrary, many ships have been observed where 

 the fouling growths were very probably killed by the entrance of the ship into a fresh- 

 water harbor, but fouling on such ships often remained severe for a considerable 

 period. The shelly growths of barnacles, oysters, Mytilis, and even of Bryozoa, and 

 the chitinous "stems" of hydroids have been seen on ships that had been in the 

 fresh-water harbor of Philadelphia for more than 12 months. The most notable 

 example of this is the case of the destroyers ParTcer and O'Brien (November 28, 1922), 

 where many barnacle shells were scraped from their bottoms after more than 20 

 months in polluted fresh water. It is thus evident that although fresh water kills 

 the growths that cause fouling, it does not remove them or clean the ships unless 

 such growths are succulent or very young, in which cases the entire ship probably is 

 cleaned by this process. 



EXPERIMENTAL DATA 



In order to ascertain more exactly the period that it is necessary a vessel spend 

 in fresh water in order to secure such desired results, the following experiments were 

 conducted. 



Various types of organisms were removed from their normal salt-water habita- 

 tion and placed in containers, through which a slow current of fresh water passed 

 constantly. A continuous circulation of water was found necessary, both to supply 

 the required oxygen and to prevent putrefaction from affecting the more resistant 

 organisms. Death point was determined if after transfer to normal environment 

 resuscitation did not occur. 



In Table 6 is given the list of the organisms tested and the period of exposure 

 necessary to kill. The first column indicates the time at which the first were ob- 

 served to succumb, and the second column indicates the maximum period during 

 which these organisms were able to live in fresh water. The number of trials is also 

 indicated in each case, many organisms being used in each trial. 



It will be seen from this table that many of the organisms that cause folding can 

 be killed by transfer to fresh water for a period of 24 hours. This is especially true 

 for most larval and young forms. It wiU be noted, however, that several important 

 organisms such as Balanus eburneus, Ostrea, and Enteromorpha, often are not killed 

 in less than four days, although in several tests it was foimd that the larvae and 

 younger forms of all but the last of these were killed within that period. 



