216 



BXriiLETIN OF THE BUEBAXT OF FISHERIES 



Freight vessels and most of the active naval vessels form the next class of ships. 

 These ships frequently lie in one port or another from one to three weeks, or even 

 longer, and offer ample opportunity for a dense "set" of fouling growths to take 

 place. The degree to which these organisms continue to grow depends very largely 

 upon the amount of time in excess of 10 days that is spent in any one port and to an 

 equal degree upon the successive ports visited after the acquisition of the original 

 "set." If these ports should be in close proximity, the growths will continue to 

 develop as if the ship were in the original port (with some exceptions), but if con- 

 siderable distance (500 miles or more) separates them, most, if not all, of the fouling 

 is killed, and if less than 2 weeks old almost all will drop off when dead. 



PER CENT OF NUMBER OF SHIPS INEACH GROUP 



FiQ. 23.— Eelation between type (and related duty) of a ship and the amount of fouling, disregarding factor of time 



Another class of ships, including commercial ships lying idle in port either for 

 overhauling, repairs, or other reasons, as well as many of our naval craft (in peace 

 times), forms the group that is fouled most heavily. This is due largely to the fact 

 that frequently they he in a given port for from 1 to 6 months, affording ample time 

 for the original set of fouling material to develop and grow, so that all types of sessUe 

 marine growths that normally occur in that harbor frequently are found in luxurious 

 growth on the bottoms of such ships. 



An analysis of the data in Table 1 , as regards the relation of fouhng to the above 

 classes of vessels, is given in Figure 23, which shows the percentage of the total 

 number of ships in each of the eight classes, grouped according to the relative amount 



