230 



BULLETIN OF THE BUREAU OF FISHERIES 



Table 6. — Illustrating the resistance of marine organisms to the effects of fresh water, indicating in 

 hours the length of time that certain forms , common on ship's bottoms, were able to live in circulating 

 fresh water 



Organism 



Number 

 of trials 



Minimum 



Maximum 



period 



period 



Hours 



Hours 



72 



96 



12 



24 



36 



48 



48 



60 



12 



24 



6 



12 



6 



12 



12 



24 



6 



12 



48 



96 



72 





Balanus eburneus _. 



B. amphitrite 



B. balanoides (1) 



Chthamalus stellatus (2) 



Tubularia crocea 



Eudendrium 



Obelia geniculata 



Membranipora sp.? 



Bowerbankia gracilis 



Ostrea elongata 



Enteromorpba (3) 



Note. — (1) and (2) are not common on ship's bottoms but are listed for the sake of comparisons. (3) is a variable, depending 

 upon the previous environmental conditions. Death determined by inability to revive after being returned to original environ- 

 ment. 



Accordingly, it can be assumed that much fouling is killed by a stay of one day in 

 fresh water. If the growths present are all young, a larger percentage will be killed 

 and most or all of them will disappear completely. If on the other hand, they are 

 mature forms of more than two or thi*ee months, many of such growths may not be 

 killed in less than 72 or 96 hours; and even if killed, their shelly structures will still 

 remain, often for a long period of time. Inasmuch as the resistance to a ship is caused 

 by these structures, whether alive or dead, little benefit will accrue from such visits 

 to fresh water, except that these growths will no longer increase in size. It is accord- 

 ingly evident that fresh water will kill most forms that cause fouling but will not 

 remove many of the growths already present, unless these are minute and not heavily 

 calcified or chitinized. 



POISON PAINTS, METALS, AND SURFACE FILMS 



POISON PAINTS 



The practice of painting ships' bottoms has been in vogue so long that its value 

 hardly can be questioned. As stated in the introduction, ships probably have been 

 painted since the first ship was launched, but the nature of this paint has varied 

 from time to time. These paints have been utilized as much or even more for the 

 preservation of the wood or metal of which the hull is made than for the prevention 

 of marine growths. Thus, on steel vessels to-day it is the practice to cover the ship 

 first with a coat of " anticorrosive " paint and subsequently with a second coating of 

 some " antif ouling " paint. The former is for the preservation of the metal while 

 the latter is applied in the hope of preventing the growth of fouling agencies, and 

 contains the various poisons used for that purpose. 



Before metal vessels came into use poison paints were resorted to primarily 

 to prevent the attachment of the marine borers, which, even in recent times, have 

 caused so much destruction to piling and other harbor equipment (see Atwood and 

 Johnson, 1924) and which, until steel ships were first employed, caused even greater 

 damage to the hulls of wooden vessels. 



