FOULING OF SHIPS BOTTOMS 



(2) The Significance of Fouling. 



The fouling of shij)s by marine growths is a matter of very great 

 importance in both the performance and the upkeep of the Roj^al 

 Navy and merchant fleets. 



For design purposes it is the practice of the Admiralty to allow 

 an increase of frictional resistance of }% per day out of dock in 

 temperate waters and J% per day in tropical waters. These figures 

 are based on the results of experience over a number of years, and 

 may be regarded as covering the worst conditions of fouling that 

 are generally experienced in warships in peiace-time, when a rela- 

 tively large proportion of time is spent in harbours. The possible 

 elfeet of fouling in producing increased fuel consumption and loss 

 of speed is shown in Table I., which is calculated on the basis of 

 this Admiralty allowance for various types of ships in temperate 

 waters. The corresponding figures under tropical conditions would 

 be approximately doubled. 



Table I, — Effect of Fouling for Six Months out of Dock in Temperate 



Waters. 



Frictional resistance assumed to increase |'\, per day. 



* These figures are based on the fuel consumptions for propulsion ojily, 

 i.e., auxiliaries are not included. 



The foregoing examples refer to warships under peace coiulitions. 

 The correspondhig figures for merchant ships will in general be less, 

 because they spend a greater proportion of time at sea and are there- 

 fore less exposed to fouling conditions. During the war, however, 

 many serious cases of fouling of merchant ships have been reported, 

 pai'ticularly on vessels operating in the tropics. As a result, the 

 Ministry of War Transport and shipowners have been considering the 

 possibility of using more efficient compositions to meet these con- 

 ditions. 



\Vhilst it is difficult to give a reliable estimate, it is probable that 

 at least 20 ^o of ^be total quantity of fuel used for ship propulsion is 

 expended in overcoming the increased resistance due to fouling. 

 When to this is added the cost of the more frequent dry -dockings 

 necessary for cleaning and coating bottoms, some idea can be obtained 

 ( )f the enormous expenditure attributable to fouling. A part from the 



