environmental hazards and how they affect 

 submersible operations is presented in refer- 

 ence (4). 



Natural Hazards 



Weather: The effects of Weather on sea state 

 and its influence on launch/retrieval are dis- 

 cussed in Chapter 12. A further problem 

 arises when waves higher than 4 or 5 feet 

 make visual sighting of submersibles ex- 

 tremely difficult owing to their low silhou- 

 ette. Although radio contact can be made, 

 homing on submersibles is accomplished visi- 

 bly and, in some instances, as much as 3 to 4 

 miles may separate support ship and sub- 

 mersible. This condition makes visible sight- 

 ing of a low silhouette vehicle almost impos- 

 sible. Deterioration of weather during the 

 dive may affect not only the subsequent re- 

 trieval of the submersible, but the transfer 

 of personnel to the support craft. 



Currents: While the major ocean surface cur- 

 rents are generally known and their posi- 

 tions charted, little data exist concerning 

 near-bottom currents where the submersible 

 may be required to operate. Near-bottom 

 currents are variable in both direction and 

 speed over short periods of time, and they 

 are strongly affected by topography. Short- 

 term shifts in current speed and direction 

 are common and have caused severe opera- 

 tional problems in an area where less than 

 0.1 knot was observed at commencement of a 

 survey and over 3 knots were present at its 

 termination (5). Control of the low speed 

 submersible is almost impossible under such 

 conditions, and the problem of avoiding man- 

 made or natural hazards is magnified sub- 

 stantially. 



Where extensive shallow water or enclosed 

 areas are situated adjacent to a deep ocean 

 area, a current may be generated by the 

 differences in water densities between shal- 

 low and deep areas. 



An example is the Strait of Gibraltar 

 where water of greater density than contig- 

 uous Atlantic waters exits the strait due 

 west along the bottom and then descends to 

 a depth of over 3,000 feet where it spreads 

 along areas of equal density. The danger of 

 such a current is particularly significant to 

 the low-speed, shallow-diving submersible 

 which may get caught in the current and be 



carried to areas in excess of its collapse 

 depth before remedial action can be taken. 



Sediments: The likelihood of being inundated 

 by a turbidity current created by natural 

 causes is probably very slight. The prospect 

 however, of a submersible causing a turbid- 

 ity current or sediment slide is possible and, 

 in fact, has occurred. 



During a dive into Toulon Canyon in the 

 FNRS-3 , the vehicle apparently broke a 

 block of mud loose causing a mud slide or 

 turbidity current (6). A sediment cloud was 

 generated which reduced visibility to zero. 

 In an effort to clear the sediment cloud, 

 FNRS-3 steered across the canyon on a de- 

 scending course and ran into the opposite 

 wall at a depth of 5,250 feet. After more than 

 an hour's wait, the sediment cloud caused by 

 impact with the opposite wall had not 

 cleared; the vehicle began ascent and finally, 

 at a height of 800 feet above the bottom, 

 visibility returned. 



An additional hazard would occur if the 

 slide or avalanche weakened the formation 

 above the vehicle. Under these conditions it 

 is conceivable that a sufficient quantity of 

 sediment can settle on a small submersible 

 to prohibit the vehicle from ascending. In 

 this regard, a submersible may collect mud 

 through openings in the exostructure and 

 keel — a more likely, but less obvious, means 

 of accidentally gaining large mud weight. 

 ALUMINAUT picked up 4,000 pounds of mud 

 in its keel tanks when it inadvertently slid 

 down a slope during an H-bomb recovery 

 mission off Palomares, Spain, in 1966 (7). 



Topography: Knowledge of ledges, overhangs 

 and sheer walls observed in some areas of 

 the ocean is of utmost importance to the 

 submersible operator, who is generally re- 

 stricted to limited visibility and little or no 

 upward viewing capability. Though the sub- 

 mersible operator may operate with caution, 

 even the most competent pilot can find him- 

 self in an unfavorable position. 



During operations in the La Jolla Canyon, 

 DIVING SAUCER entered an area of the 

 canyon where the upper walls began to over- 

 hang and the distance between the walls 

 became progressively less. Finally, the can- 

 yon narrowed to such an extent that the 

 vehicle could not ascend due to the overhang 



631 



