recorded on the meter is directly propor- 

 tional to the amount of shot in the tank, 

 since the level of shot represents the amount 

 of mutual coupling between the two coils 

 and, hence, the induced voltage on the sec- 

 ondary. 



A specially constructed timer is installed 

 in the pilot's console and consists of two stop 

 watches each connected to one of the shot 

 ballast circuits. The timer automatically 

 starts and stops as shot ballast is metered 

 out of each hopper. The quantity of shot 

 jettisoned by the operator is simply calcu- 

 lated by time units as 4.4 pounds of shot fall 

 through the valve per second. 



An emergency shot ballast system was in- 

 stalled to provide a quick release of ballast in 

 case of flooding or some other emergency 

 requiring rapid surfacing or extra buoyancy. 

 Hydraulic pressure (140 kg/cm^) is built up in 

 an accumulator which in turn holds a port 

 and starboard hydraulic piston in a position 

 that prevents a trap door at the bottom of 

 each tank from opening. By opening a valve 

 that allows the hydraulic fluid to return to 

 the reservoir, hydraulic pressure is released 

 on the piston which in turn allows the trap 

 door to open. (The weight of the shot causes 

 the piston to move to the opposite end of the 

 cylinder when hydraulic pressure is re- 

 leased.) The trap door, hinged on the oppo- 

 site side, allows the shot to drop rapidly. If a 

 piston fails to move due to corrosion or some 

 other reason, hydraulic fluid can be forced to 

 the opposite side of the piston to provide an 

 additional force. By operating valves in rapid 

 succession, the entire operation, including 

 power to the opposite side of the piston, is 

 accomplished very quickly. 



Seals at each end of the piston prevent 

 seawater from entering the cylinder. Around 

 the rod is fitted a stainless steel cylinder or 

 sleeve capped with a rubber boot. The cylin- 

 der is packed solid with grease and the boot 

 can move in and out slightly with sea pres- 

 sure. This end of the piston is untouched by 

 seawater and cannot corrode. 



If the boat has been towed or in port for 

 several days just prior to diving, the trap 

 door/piston mechanism is tested by having a 

 diver install a special screw fitting in each 

 tank that holds the trap door in place. The 

 piston is then moved by applying power in 



the opposite side of the cylinder and a diver 

 can observe whether or not the piston re- 

 tracts. 



The logistics involved with steel shot bal- 

 last can be somewhat restrictive on open-sea 

 operations. Because the majority of sub- 

 mersibles using this method are too large to 

 be launched and retrieved for each dive, they 

 must be replenished while in the water. Gen- 

 erally, this is accomplished in a harbor or 

 protected area (Fig. 6.8) where the sea state 

 is not a problem; however, on occasion it is 

 necessary to transfer shot at sea. When this 

 is the case, it can be quite difficult transfer- 

 ring several thousand pounds of shot in 25- 

 pound bags from the support ship to the 

 vehicle. 



Gasoline: 



The positive buoyant force on all bathy- 

 scaphs is derived from gasoline contained in 

 a metallic float. Several factors enter into 

 the selection of petroleum hydrocarbons for 

 deep-water buoyancy applications: 

 — Gasoline is readily available and at rela- 

 tively low cost. 

 — Although not as effective as air at shal- 

 low depths, gasoline retains most of 

 its buoyancy at any depth. 

 — Petroleum hydrocarbons can reach a 

 density of 0.66 gm/cm^, which is good 

 relative to seawater (1.025 gm/cm^). 

 On the other hand, there are several disad- 

 vantages, the main one being flammability. 

 Unfortunately, the hydrocarbons with the 

 lowest density are the most flammable; for 

 this reason, kerosene, in spite of its high 

 density, is often used. 



The logistic and safety problems involved 

 with gasoline flotation are quite complex. 

 The U.S. Navy's TRIESTE 11 carries 75,000 

 gallons of aviation gasoline (0.76 gm/cm^) in 

 its float. The bathyscaph is first launched 

 from its support ship and then filled with 

 gasoline when clear, the entire process ac- 

 counting for some 15 to 20 hours. To return 

 to its support ship, the float is pumped dry of 

 almost all gasoline and the pressure in the 

 float is maintained by introducing gaseous 

 nitrogen, which also serves to purge the float 

 of fumes. When TRIESTE II is within its 

 support ship C4/JD) the additional 1,000 to 

 2,000 gallons of gasoline remaining in the 



300 



