6 FOULING OF ships' BOTTOMS : 



possible. In all this work the importance of providing efficient 

 protective undercoats has been stressed, since premature failure of 

 the undercoats invariably leads to unrestricted fouling, apart from 

 the incidence of corrosion troubles. 



It will be realised that the problem of fouling is indeed a complex 

 one requiring the collaboration of the marine biologist and other 

 specialists. It is equally desirable that all those who are concerned 

 with ships and shipping at sea or in dock should be familiar with the 

 broader aspects of the problem and the methods by which it is being 

 tackled. It is hoped, therefore, that this booklet will serve a useful 

 purpose in stimulating the interest and co-operation of all concerned, 

 and at the same time provide a useful guide to the identification of 

 the marine organisms which cause fouling. 



(5) The Fouling Organisms. 



On a ship that has remained for a long period of time in a har- 

 bour and is then dry-docked, perhaps in that same harbour, without 

 an intervening sea voyage, an enormous number of different types 

 of organisms may be found growing. Not all of these forms are 

 attached to the surface of the vessel, for in the miniature forest of 

 growth all sorts of creeping and swimming forms find a comfortable 

 berth. In addition, many of the attached forms have anchorages 

 which will not stand up to the rapid motion of a ship at sea. In this 

 booklet attention will be concentrated on those forms which are 

 likely to be found in the normal course of a vessel's work, when she 

 is dry -do eked at the end of a trip with relatively Kttle opportunity 

 for the settlement of the temporary lodgers which may occur in the 

 harbour and approaches to dry-dock' areas. 



The limitation of the description to the " permanent " lodgers 

 has two advantages : There are surprisingly few types to describe, 

 which simplifies the problem of identifying them ; also, since the 

 temporary inhabitants will aU be rapidly washed off when the ship 

 puts to sea, they are not important in causing resistance to the 

 motion of the ship. 



Marine fouling growths appear either as slimes, as tresses of 

 marine plants or in the highly individual forms shown by the marine 

 animals. The animals and slime may occur over the whole sub- 

 merged surface ; the tresses produced by plant growth rarely extend 

 more than a few feet below the water-line. 



(a) Slimes. 



The nature of the slimes that occur on ships can be recognised 

 only b}^ microscopic examination. Commonly they appear structure- 

 less under a magnification less than X 100, and such slimes are 

 probably formed by bacteria. Others, which are usually rather 

 tougher, are formed by one-celled plants called diatoms. They live 



