FOULING OP SHIPS' BOTTOMS 



213 



91 with hydroids, 87 with Bryozoa, 37 with mollusks, 22 with tunicates, and 17 with 

 Protozoa. It is clearly evident, however, that for most vessels barnacles are the 

 most important fouling agent, while the hydroids and algae form the next groups, in 

 order of importance. These relations are shown in Table 3, where the occurrence 

 of each kind of organism is tabulated for each of the first 100 ships. 



0 50 100 150 200 250 



TOTAL NO. SHIPS EXAMINED 

 TOTAL NO. SHI PS FOULED 

 SHIPS WITH BARNACLES 

 SHIPS WITH ALGAE 

 SHIPS WITH HYDROIDS 

 SHIPS WITH BRYOZOA 

 SHIPS WITH MOLLUSCS 

 SHIPS WITH TUNICATES 

 SHIPS WITH PROTOZOA 



Fig. 21.— Number of ships fouled by each of several groups of organisms 



EFFECTS OF FOULING 



As Capt. H. Williams has very aptly stated, "considering the fact that frictional 

 resistance is the most important element in the resistance to propulsion of practically 

 all ships, it is surprising that there has been little investigation of the possibility of 

 reducing skin friction to a minimum. Ship owners seem satisfied that everything is 

 accomplished by the present system of docking ships periodically," and the subsequent 

 cleaning of their bottoms and painting with antifouling compositions. He states, 

 further, that "the effort to drive foul ships at full speed has burned many tons of fuel; 

 the normal fuel consumption of ships is in excess of what this consumption would be 

 with clean, freshly painted bottoms. While probably it is not possible to prevent 

 fouling and the consequent increase in fuel consumption, there is room for definite 

 improvement over existing conditions." 



A few studies on the effect of fouling, as regards increased resistance, have been 

 made. Thus, McEntee (1915) studied the relation of fouling to increased frictional 

 resistance by submerging, near the navy yard at Norfolk, Va., a series of steel plates, 

 each weighing 10 pounds and measuring 2 by 10 feet. After periods ranging from 1 

 to 12 months he removed the plates from the water, shipped them to Washington, 

 D. C, and, at the experimental model basin, tested their resistance at speeds ranging 

 from 2 to 8 knots. The maximum increase in resistance was found to be four times as 

 great as when such plates are clean and freshly painted. The amount of fouling was 

 determined in all cases, and the maximum foul condition of these plates would be 

 roughly comparable to the condition listed as slightly less than "moderately fouled" 

 in previous tables and elsewhere in this paper. 



