To date, two active approaches have been experimented with for minimizing the extent 

 and severity of biofouling. Both approaches rely on periodic mechanical wiping of the sur- 

 faces to keep them free of biofouling. The first approach utilizes an electrically driven wiper 

 that cleans the surface for about 1 min several times a day. The wiper may take the form of 

 an elastomeric squeegee or of a revolving brush. In either case, the motor-driven wiper sweeps 

 the surface clean several times a day, thus preventing sealife from establishing a firm foothold 

 on the transparent panel cover. A wiper in the form of a revolving brush was successfully 

 used to keep an acrylic viewport in an underwater habitat free of biofouling for 6 months. 

 Based on this experience there is no doubt that the viewport could have been kept clean for 

 an indefinite period of time, providing the wiper did not malfunction. The second active 

 approach is suitable only for buoys located at those depths where the water is subjected to 

 circular motion imparted by the action of surface waves. The wiping action is accomplished 

 in a random pattern by many wipers that consist of short lengths of plastic rope attached to 

 the buoy around its circumference. The wave-induced circular motion of the water causes 

 the rope's segments to undulate and repeatedly strike the surface of the buoy. The repeated 

 contact between the plastic rope and the panel keeps them free of biofouling. 



The advantages of the electrically powered wiper approach are that the wiping action 

 is independent of depth and wave action and that its frequency and duration can be pro- 

 grammed for the severity of biofouling that the panel may encounter during its deployment 

 in the ocean. Its disadvantages are the drain on the energy output of the solar cell panel, the 

 cost of wiper train components, and the increased overall complexity of the buoy. The 

 advantages of the wave-powered wipers approach include its simplicity, independence from 

 electrical power supply, low cost, and high reliability. Its disadvantages are shading of the 

 light-sensitive solar cell surfaces by the presence of many wipers, unpredictability of frequency 

 or duration of wiping action, and dependence on sustained duration of wave actions. Based 

 on these considerations, the electrically powered wipers are preferred unless lack of sufficient 

 power reserve in the installed solar cell array precludes their use. 



Thus it can be concluded that, although biofouling at shallow submersion is a serious 

 problem whose effects cannot be ignored, passive and active techniques exist that if incorpo- 

 rated in the submerged solar cell array assembly will insure maximum output of electrical 

 power without the performance degradation caused by biofouling buildup. 



DESIGN CONCEPTS 



Solar cell arrays can function as primary or secondary power supplies for all submerged 

 or floating oceanographic and navigational buoys currently powered by batteries and gas or 

 wave-driven electric generators. In many cases the power supplied by the solar cells will be 

 found to be more economical and thus readily acceptable to the user, while in a few cases its 

 cost will be found to be so much higher that there will be no reason to make a change. 



The availability of electric power from solar cells also allows the design and deploy- 

 ment of electronic devices in the ocean that have not been considered feasible because 



5. Kretschmer, T.R., et al, "Seafloor Construction Experiment SEACON 1," Technical Report R-817, Civil 

 Engineering Laboratory, Port Hueneme, California, February 1975. 



37 



