4 



FOULING OF ships' BOTTOMS : 



Plants grow predominantly at and near the water-line, and if 

 they .are abundant there they tend to discourage most t3rpes of 

 animal life in that area. Well below the water-line, and particularly 

 under the turn of the bilge, lack of hght prevents plant growth and 

 the population is largely, if not entirely, animal. 



Several factors influence the degree of fouling which may appear 

 on a non-toxic surface ; the more significant of these include the 

 season of the year, the amount of light reaching the submerged 

 surface, the temperature of the water, and, perhaps the most import- 

 ant, the geographical location of the waters concerned. The colour 

 of the painted surface is relatively unimportant. 



Many fouHng organisms have a restricted breeding period ; this 

 is illustrated in Fig. 1, which has been compiled at two observational 



Barnac/es 



Hydroids 



Ascidians 



Polyzoa 



Mussels 



Tubeworms 



Seaweeds 



Diatoms 



Fig. 1. — The Fouling Season at Caernarvon and Millport 1941-42. Heavy 

 settlement is indicated by cross-hatching, the period of lighter infection 

 by single hatching. [Ascidians = sea-squirts. Diatoms correspond chiefly 

 to those inhabiting the slime layer on ships.) 



stations, Caernarvon and Millport, during the two years 1941-42. 

 The seasonal settlement of fouling organisms naturally varies 

 according to the locality, but the diagram may be taken as being 

 indicative of behaviour around the coasts of Great Britain. In some 

 tropical ports, it is known that the seasonal variation in settlement 

 is much less marked than in home waters and that extensive fouling 

 will occur nearly all the year round. 



Fouling occurs when ships are in port or at anchor in shore waters, 

 since the usual fouling organisms live in or near shore waters. The 

 ports of the world vary considerably in their liability to produce 

 fouling. As a rule, ports in the trOpics are more troublesome than 

 those in temperate climates. Most marine fouling organism^ will 

 not survive in fresh water, and hence in ports into which river 

 waters run the- variety of plant and animal life that may appear is 

 curtailed or that acquired in a sea-water port may perish and sooner 

 or later fall off. The shells of barnacles and tubeworms remain 

 attached to the ships long after the animal is dead, but become very 

 brittle. One species of barnaele {Balanus improvisus) is reputed to 



