SECT. 5] DEEP SUBMERSIBLES FOR OCEANOGRAPHIC RESEARCH 505 



permitted to enter through a hole on the bottom of the envelope so that the 

 gasoline is in free communication with the surrounding sea. The pressure is thus 

 always equalized inside and out. Gasoline, being lighter than and immiscible 

 with water, floats on the top. 



Originally the float was divided into fourteen compartments. The two end 

 compartments were air tanks which were flooded for diving. The remaining 

 twelve were gasoline compartments, containing 28,000 gallons (106 m 3 ). For 

 "Project Nekton" the total volume of the float was increased by 6300 gallons. At 

 the same time, the two inside partitions were removed leaving 10 gasoline com- 

 partments. This provided an increase in buoyancy to offset the greater weight of 

 the new sphere and the additional ballast needed for ultra-deep diving. Origi- 

 nally 50 ft long, this modification increased the float length to 58 ft. The weight 

 of the modified float when empty is 16 metric tons; the diameter 11.5 ft. 



C. Ballast for Buoyancy Control 



The bathyscaph Trieste is an up-and-down craft with very limited horizontal 

 maneuverability. Vertical traverses are effected by buoyancy control with 

 jettisonable ballast. First of all, to provide the necessary negative buoyancy 

 for diving, water ballast (fixed liquid ballast) is flooded into the two end 

 compartments and into the entrance shaft or sas. Then additional negative 

 buoyancy, which can be finely adjusted by the pilot, is effected by releasing 

 gasoline (jettisonable liquid ballast) from the central maneuvering compart- 

 ment. This compartment has a capacity of 4 m 3 or about 1150 gallons with a 

 total lifting ability of 1.4 tons. 



Positive buoyancy is obtained by the release of iron pellets (jettisonable 

 solid ballast) like BB shot — the type used industrially for sand blasting. The 

 shot is held in two large tubs which have a funnel-shaped construction at the 

 bottom. Once the mechanical keeper is removed for diving, the shot is held in 

 place by the magnetic field induced by an electromagnet. When the magnet is 

 energized, the shot is frozen into a solid plug. When the current is cut, it falls 

 freely through the "electrochute" like sand through an hourglass. The current 

 in normal operation is manually cut by the pilot. In the event of power failure, 

 the ballast is jettisoned automatically, returning the Trieste to the surface. 

 Since the ballast must be a magnetic material, iron ballast is used in place of 

 lead. As originally constructed, the ballast tubs held 9 tons of ballast weight in 

 air. The capacity was increased to 16 tons for the ultra-deep "Project Nekton" 

 dives. 



The guide rope and the ballast tubs themselves (fixed solid ballast) are 

 attached to the bathyscaph by means of electromagnets, so that they can be 

 jettisoned at will or in emergency. If, for example, the guide rope becomes 

 fouled on the bottom, it can be cast off; the ballast tubs or silos themselves can 

 be jettisoned if the shot funnel should become plugged for any reason. 



Inherently the bathyscaph is dynamically unstable since gasoline is more 

 compressible than water. For example, if the surface temperature is 30°C and 



