tial pressures of perhaps 7 or 8 thousand psi 

 would be required; dynamic seals for these 

 pressures are not available. To further com- 

 plicate the problem, the pressure hull itself 

 is not structurally stable and can be ex- 

 pected to shrink as the vehicle goes deeper. 

 ALUMINAUT is calculated to lose 1 inch in 

 length and 0.1 inch in diameter at 15,000 feet 

 (17). Such characteristics further complicate 

 the difficulties of mechanical penetrations on 

 deep submersibles (greater than 1,000-ft 

 depth), and is a prime reason for their gen- 

 eral absence. 



Nonetheless, mechanical penetrations are 

 included on the shallow vehicles and in some 

 cases on deep vehicles where their advan- 

 tages are seen to outweigh their disadvan- 

 tages. The following presents the functions 

 of mechanical penetrators found on vehicles 

 today. 



a) Propellers and Thrusters: In vehicles 

 such as SEA OTTER, DEEP DIVER and the 



NEKTON series, the main propulsion motor 

 is housed in a watertight box penetrated by 

 a shaft to drive the main propulsion unit or a 

 thruster. The motor container is separate 

 from the hull as a safety precaution, and the 

 shaft, in DEEP DIVER's case, is sealed by a 

 shoulder bearing against two sleeves 

 screwed into the penetration and an 0-ring 

 for low pressure protection. 



b) Dive Planes and Rudders: Some shallow- 

 diving vehicles include hull penetrations for 

 manual control of diving planes and rudders. 



c) Hatch Shafts: Several vehicles include a 

 mechanical penetration through the hatch 

 which serves as a leverage or rotating point 

 around which the hatch seals are closed or 

 opened (Fig. 5.12). 



d) Weight Drop Shafts: The greatest num- 

 ber of mechanical penetrations are for the 

 purpose of dropping weights, generally in an 

 emergency, to gain positive buoyancy. This 

 type of penetration only rotates in one plane 

 and is preferred over electric weight drop- 

 ping actuators owing to the possibility of 

 electrical failure. ALVIN incorporates such 

 an arrangement to separate the sphere from 

 the entire exostructure. 



e) Manipulators: The NEKTON-c\ass sub- 

 mersibles provide a mechanical penetration 

 for a 3-ft-long steel rod which is manually 



pushed out or pulled into the vehicle. The rod 

 incorporates a claw at its outer end and can 

 grasp samples as desired. According to Dr. R. 

 F. Dill (NOAA, personal communication), at 

 1,000 feet the pressure shrinkage of the hull 

 causes the arm to come down with "arthri- 

 tis," and considerable effort is required to 

 manipulate the device. 



f) Hull Vents: Several submersibles con- 

 tain penetrations for replenishing the pres- 

 sure hull air or to equalize hull air pressure. 

 In the first case snorkels are employed for 

 surface cruising. In the latter case (BEA- 

 VER) a valve is activated in an emergency 

 which brings main ballast air into the hull 

 and builds pressure up to ambient so that 

 the passengers may open the hatch and exit. 

 The All Ocean Industries' submersible has a 

 curious arrangement whereby the main bal- 

 last tanks vent into the pressure hull. To 

 prevent a buildup of air pressure a second 

 valve, connected to a snorkel, is opened and 

 the air vents outboard. The operating in- 

 structions for the submersible cautions the 

 operator to secure the ballast tank vent 

 valve as soon as a little water appears in- 

 board. 



Viewports: 



In an extremely detailed and comprehen- 

 sive paper, NCEL engineers Snoey and 

 Stachiw (22) present the history, application, 

 advantages and disadvantages of materials 

 and shapes for submersible viewports. The 

 basis for their report rests in a series of 

 exhaustive tests and analyses of viewports 

 and their materials at NCEL. The reader is 

 referred to this report and its references for 

 detailed aspects of viewport design and ma- 

 terials capabilities. 



Three materials have been used for view- 

 ports: fused quartz, acrylic plastic and glass. 

 The first of these was used by Beebe in the 

 BATHYSPHERE, but his difficulties with 

 cracking and chipping persuaded the elder 

 Piccard to look for an alternative, which 

 proved to be acrylic plastic. Acrylic plastic is 

 now the accepted viewport material for all 

 but two submersibles; KUROSHIO II and 

 YOMIURI both use glass. 



Table 5.5 presents the properties of glass 

 and acrylic plastic. In essence, where one is 

 strong, the other is weak. According to refer- 



258 



