194 



BULLETIN OF THE BUREAU OF FISHERIES 



the effect of marine borers recently has been studied extensively by others (Atwood, 

 1924), while the problem of corrosion has but little relation to this biological study. 



The economic importance of the fouling of ships' bottoms rarely is realized by 

 anyone who is not informed regarding the very special problems relating to the 

 maintenance of ships. The factors that contribute to the importance of this 

 problem may be outlined briefly, as follows: 



1. Speed diminished up to 50 per cent. 



2. Voyage delayed from 10 to 50 per cent of total time. 



3. Increase in fuel consumption up to 40 per cent additional. 



4. Increase in wear and tear on machinery. 



5. Necessity for dry docking, cleaning, and painting after every six or eight 

 months. 



6. Loss of time for above, amounting to about one month out of every year. 

 It has been estimated conservatively that more than $100,000,000 is spent 



annually by the shipping interests of the United States alone because of fouling. 

 When one realizes that fouling often increases the resistance of a ship in water, so 

 that the fuel consumption must be increased 30 per cent in order to maintain a given 

 speed, and that for more than half of the time between dry dockings for any vessel 

 that operates at sea, after the first month, such costs probably are increased by a 

 minimum of 10 per cent, the expense due to increased fuel consumption alone assumes 

 large proportions. 



It is the practice of most shipping concerns to "clean" the bottoms of their 

 vessels every six or eight months. In order to do this the bottoms are exposed to 

 view, either by the use of dry docks or marine railways. The former are of two 

 types — the graving dry dock and the floating dry dock. Lighter craft frequently 

 are removed from the water by a marine railway. The cost of maintaining and 

 operating such equipment can be charged largely to fouling. The large sums of 

 money involved can be realized when one learns that it costs approximately $100,000 

 to dry-dock, clean, and paint the bottom of a vessel such as the Leviathan or the 

 Majestic, for these ships have more than an acre of surface exposed to the action of 

 the sea and which must be cleaned and painted every time these vessels are dry- 

 docked. It must not be forgotten, also, that during the period in dry dock the cost 

 of maintaining the ship and its crew remains constant, while the operating income 

 is reduced to nothing. The time spent in dry dock varies with conditions from three 

 days to three weeks, or more; but for the ships listed in this report the average is 

 seven or eight days. This process of cleaning is illustrated in Figure 1 . 



In addition to its economic importance, this problem has an important relation 

 to the question of national defense. An able Navy has long been held to be the 

 greatest force for defense that a country such as the United States can possess. 

 Under present conditions, speed of such vessels is of increasing importance. If, 

 then, fouling decreases the speed by as much as 40 per cent, the efficiency of such 

 crafts is lost and critical delays might result. 



From a biological point of view, this problem has several interesting aspects. 

 The ecology of the organisms that five at some depth in the ocean has been difficult 

 to study, because it has been impossible to bring them to the surface in sufficient 



