trapped the vehicle below. One major advan- 

 tage that submersibles — like the scuba di- 

 ver — enjoy is maneuverability. To restrict 

 this maneuverability may place it in greater 

 jeopardy than is the chance of going below 

 operational depth. It should be noted, how- 

 ever, that the Japanese KUROSHIO I & II 

 have conducted safe dives for well over a 

 decade with a power cable tethered to a 

 surface ship. Undoubtedly, this safety record 

 is the result of careful planning and investi- 

 gation of the dive sites to assure that noth- 

 ing is present to foul the cable. 



Impact With Bottom 



Owing to the inherent inaccuracies in 

 depth gages and precise depth values at the 

 dive site, many vehicles include a device 

 which informs the operator of his distance 

 off the bottom. In addition to supplying data 

 useful to performance of missions, such de- 

 vices afford the operator the opportunity to 

 avoid striking the bottom on descent and 

 damaging critical components. Conventional 

 echo sounders serve this purpose and include 



a transducer mounted on the vehicle's keel 

 and a depth display device in the pressure 

 hull. The internal display is either a strip 

 chart recorder or a flashing light. Either 

 display is adequate, but the strip chart pro- 

 vides a permanent record which is invalua- 

 ble to various surveying or research tasks. 

 Regardless of the sensing device employed, 

 one may expect some inadvertent contact 

 with the bottom as the underside ofDS-4000 

 (Fig. 14.1) testifies. 



Obstacles to Maneuvering 



Underwater visibility may range from sev- 

 eral hundred feet (Fig. 14.2) to a few feet — 

 the former being common to shallow tropic 

 and sub-tropic waters and in the arctic and 

 antarctic, while the latter is found through- 

 out the estuarine, coastal and open ocean 

 temperate waters. The lack of usable am- 

 bient light for visual observations below a 

 few hundred feet requires artificial lighting. 

 This may provide 50 to 70 feet of viewing 

 distance, depending on water clarity. Conse- 

 quently, many submersibles carry a sonic 





J 



r i} 



Fig, 14.1 Scratches on Ihe underside of DEEPSTAR 4000 testify to the frequency of inadvertent tjoltoming in submersibles (NAVOCEANO) 



656 



