Disadvantages of the submersible include: 



1. It requires engineering development for underwater cleaning appli- 

 cation. Existing subraersibles must be integrated with robot-controlled, 

 exterior-mounted cleaning systems. 



2. Large size limits accessibility to confined spaces. 



3. Submersible becomes complex when equipped to inspect, document, 

 and clean. 



Existing cleaning procedures for underwater hulls are generally not 

 applied deeper than 8 m. Greater depths could be achieved if diver capa- 

 bility is upgraded. Existing underwater cleaning procedures provide divers 

 with surface supplied air. Air diving without decompression limits the 

 cleaning of the OTEC plant to a depth of 15 m because bottom times at 



greater depths are too short to perform labor-intensive work. Practical 



119 

 bottom times of 1 1/2 hr below 15 m require decompression; therefore, 



the use of a diving bell to transfer the divers to the surface and a decom- 

 pression chamber on the deck is necessary. In addition, a minor modifica- 

 tion of the cleaning equipment to pressure-proof critical fittings is 



120 

 necessary below 15 m. Extended bottom times at depth below 40 m for 



1 1/2 hr or more are feasible, but are further complicated because mixed- 

 gas diving systems are required. Mixed-gas or saturation diving requires 

 greater diver skill and considerable surface support. If OTEC field 

 experience dictates fouling removal at depths below 40 m, the engineering 

 development of a tethered submersible cleaning vehicle may be a simpler, and 

 more direct approach. The conceptualized vehicle would have mechanical 

 arms to operate brushes or jets to defoul and a TV camera and video tape 

 equipment to inspect and document the surface conditions before and after 

 cleaning. 



State-of-the-Art Cleaning Equipment 



Diver-Operated Rotary Brushes . Many underwater cleaning operations are 

 performed using circular brushes (25 to 36 cm in diameter) fitted to a 

 single diver-held mechanical rotary scrubber (Figure 8) . Various types of 

 brushes with different bristle arrangement, bristle length, and materials 

 are available. The bristles may be made of steel, plastic, or plastic- 



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