In April 1957 the collection of a 12- month series of data was com- 

 pleted. The study was continued for another year at the present 

 location (Fig. 1) to verify the first year's data. In addition, another 

 rack of test panels was submerged at a location farther out in the 

 channel to ascertain the type of spatial variation to be expected. 

 The results reported here will be substantiated or modified based on 

 these additional data. 



II. METHODS AND MATERIALS 



Figure 1 shows the test location in Chesapeake Bay. The following 

 considerations were used in the selection of the site. The site had to 

 be close enough to the channel to be representative of the type of 

 fouling occurring in the channel. However, ship traffic precluded 

 locating it directly in the channel. The site had to be somewhat pro- 

 tected so that a small diver's boat (a converted LCM) could operate at 

 the location in rough weather. It also had to be located in a depth of 

 water which would not be unduly restrictive on diver descent and ascent. 

 The location chosen was near a shoal-marker buoy at the edge of 

 Thimble Shoal Channel in 38 feet of water. 



A fouling rack, designed and built by personnel of the Mine Hunting 

 Unit, was constructed so as to have sufficient weight and stability 

 to remain in place on the bottom under conditions of strong current 

 flow, such as occur in this area. The rack was designed to hold 13 

 fouling test panels in a vertical position suspended 3 feet off the bottom. 

 The test panels were attached to the rack by means of hooks which 

 permitted easy removal and replacement by suited divers wearing 

 heavy gloves. Figure 2 is a sketch illustrating the construction of the 

 rack. Figure 3 is a view of the rack prior to placement at the test 

 location. 



The test panels, which had been cut out of mine cases, were curved 

 steel plates 15 1/4 inches by 8 inches by 1/8 inch, weighing 68 ounces 

 and having a total surface area of 1.7 square feet. The panels were 

 painted with standard black enamel which is used routinely on ground 

 mines. Holes were drilled through the panels to permit suspension 

 from the hooks on the rack. 



The rack was submerged, and 12 test panels were attached by a 

 diver. The location was visited at regular monthly intervals, and 

 test panels were removed and replaced according to a schedule 

 designed to expose themfor various lengths of time from 1 to 12 months. 

 Figure 4 shows the panel manipulation schedule and the exposure 



