220 



BULLETIN OF THE BUREAU OF FISHERIES 



cruisers about 20 per cent, battleships about 15 per cent, and colliers about 10 per 

 cent, while it will be realized that lightships and " out-of-commission " ships spend 

 virtually none of their time cruising. 



That this factor is of great importance can be seen from a careful study of the 

 list of ships, their docking periods, cruising time, and amount of fouling, given in 

 Table 1. It has been considered desirable, however, to present this information 

 more fully and compare it from several points of view. 



Accordingly, in Figure 25 the amount of fouling in relation to the time spent in 

 port, regardless of all other factors, is represented in the form of a diagram. As 

 can be seen from this diagram, fouling increases in direct relation to the amount of 

 time spent in port. 



TIME: PERCENTAGE OF SHIPS IN EACH GROUP 



0 10 20 30 40 50 60 70 80 90 100 



v///////^y////m^:wm 



IN 



0-3 



MONTHS 4-6 

 SINCE 7-9 

 LAST 10-12 

 PREVIOUS 13-15 

 DRY- 16-1 8 

 DOCKING 19-21 



12 



13 ^M^Mg 



9 w^^^m^^^^ & 



y//////\w//////m$m\ i w 



w///:4y/»w5 



□ 



CLEAN 



LIGHTLY 

 FOULED 



MODERATELY 

 FOULED 



HEAVILY 

 FOULED 



Fig. 26. — Relation between amount of fouling and amount of time between dry dockings 



In Figure 26 the amount of fouling in relation to the total period that elapsed 

 since the previous dry docking is shown. It can be seen, by referring to this dia- 

 gram, that there is a fairly steady increase in the amount of fouling with the lapse 

 of time, regardless of all other factors. Although this diagram presents only rela- 

 tive values, and at best approximate, it shows clearly, however, that the rate of 

 fouling is virtually constant from the moment one dry-docking period ends to the 

 time the next begins. (If the protective paints used have a definite "length of life" 

 for efficiency as an antifouling agent, as is generally maintained, then there should 

 be a marked turn at some point in the diagram, presumably after six or eight months, 

 on the basis of customary dry-docking schedules.) 



In Figure 27 is shown the relation of fouling to the amount of time spent cruis- 

 ing. This diagram is the reverse of that shown in Figure 25 and will serve to 

 emphasize the significance of cruising in its effect on fouling. It will be seen that 

 the amount of fouling is decidedly less the longer the period of time spent cruising. 



