some soft— bodied forms may be removed from the 

 moving ship by the friction of the water. Conse- 

 quently, a ship which lies at anchor for long pe- 

 riods is much more likely to foul than an active 

 ship. Since most of the forms which attach in 

 tropical waters cannot live in cold water, a ship 

 which cruises north and south frequently has less 

 fouling than one that stays in the same latitude. 

 Fresh water will kill most of the marine fouling 

 forms. The large shells of the adults will re- 

 main after the animal is dead, however, so that a 

 trip into fresh water is less effective in reduc- 

 ing skin friction than is popularly supposed. 



Perhaps the most important factor influencing 

 the amount of fouling is the paint applied at the 

 last docking, and the length of time this paint 

 has been exposed to the action of sea water. 

 Paints differ considerably in their effective- 

 ness. Some are very efficient for short periods 

 of time but are rendered ineffective after a few 

 months in the water. No antifouling paint has 

 yet been invented which will be effective indef- 

 initely, but great progress has been made in the 

 last few years, and there is promise of definite 

 improvement over present performances. 



