decompression and extending it beyond spec- 

 ified time limits (see U.S. Navy Diving Man- 

 ual) at specific depths can be fatal to the 

 occupants if decompression facilities are not 

 available. The British system owes its suc- 

 cess to short bottom time, extreme simplicity 

 and protection from cold, among other 

 things. The procedures from manned sub- 

 mersibles offer few, if any, of these advan- 

 tages. For this reason, leaving the submers- 

 ible is a last resort. 



Pressure Hull Release: 



The U.S. Navy submersibles ALVIN, SEA 

 CLIFF, TURTLE and MAKAKAI are so con- 

 structed that the pressure hull (sphere) may 

 be mechanically disengaged from the exo- 

 structure and, by virtue of its positive buoy- 

 ancy, carry the occupants to the surface. The 

 principle of operation is similar in all of these 

 vehicles, and the description of ALVIN^s re- 

 lease mechanism (Mavor et al. (2)) is repre- 

 sentative. ALVIN was designed in two sec- 

 tions, the forebody and the afterbody. The 

 forebody includes the personnel sphere, the 

 conning tower, the main ballast system, an 

 emergency battery supply and all the life- 

 support equipment. It is buoyant by some 

 800-900 pounds. The remainder of the vehicle 

 comprises the afterbody. 



The frame of the afterbody was designe(^ to 

 protrude underneath the pressure hull and 

 provide a cradle for it. When in "neutral 

 trim," the afterbody is negatively buoyant 

 by the same amount that the forebody is 

 positively buoyant. A mechanical release 

 mechanism holds the two sections together 

 and is in tension when submerged. On deck 

 the mechanism is relaxed and the forebody 

 rests in the cradle of the afterbody. 



The release mechanism consists of a shaft, 

 a seal assembly, two spring-loaded dogs and 

 two hooks. The dogs are part of the afterbody 

 and the hooks are rigidly attached to the 

 pressure hull. The shaft penetrates the pres- 

 sure hull on bottom dead center. When the 

 shaft is turned with a suitable wrench it 

 rotates a cam which, at one-quarter turn 

 allows the dogs to come together and disen- 

 gage the hooks. The forebody is then free to 

 rise to the surface with the occupants (Fig. 

 14.8). 



The position of the sphere upon reaching 

 the surface is speculative. Shallow water 



tests (18 ft) under controlled conditions were 

 conducted and ALVIN''s sphere reached the 

 surface with the sail up and the hatch could 

 have been opened by the occupants without 

 flooding, but from a 12,000-foot ascent, the 

 drag on the sail could produce a surfaced 

 stable condition with the hatch down. 



Releasable Capsule: 



Similar in effect to ALVIN^s releasable 

 pressure hull are the releasable spheres on 

 the uncompleted French ARGYROISETE and 

 the Japanese SHINKAI. Atop ARGYRO- 

 NETE^s hull and over the main hatch is a 

 2.28-meter-diameter steel sphere capable of 

 accommodating the entire crew of 10 (Fig. 

 14.9). Once the occupants are inside, the 

 sphere is released by them to rise to the 

 surface. In ARGYROISETE an inflatable 

 trunk surrounds the sphere hatch and af- 

 fords protection from the sea. 



Inflatable Bag: 



Two submersibles (PC5C and TECH- 

 DIVER) offer as optional features emergency 

 bags external to the hull and inflatable by 

 carbon dioxide. These bags may be inflated 

 automatically or manually. In TECHDTVER 

 the bag capacity is 40 cubic feet. 



Entanglement 



The methods available to the submersible 

 operator in the event of entanglement de- 

 pend upon the nature of the object fouled. If 



Fig 14.8 Emergency release of ALVINs personnel sphere. 



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