opposite characteristics (19). Following many 

 trials and testing by W. R. Forman and his 

 associates at NUC, the edge of the hemi- 

 sphere joining the steel cylindrical pressure 

 hull was ground round to a radius equal to 

 one-half the shell thickness and a neoprene- 

 coated nylon gasket was fitted between the 

 two (Fig. 5.10). This configuration and very 

 careful fitting eliminated edge failures. A 

 titanium retaining ring holds both glass end- 

 cap and steel cylinder together. 



HULL PENETRATIONS 



Unlike large military submarines, a sub- 

 mersible's interior is quite limited, and items 

 such as batteries and motors are frequently 

 located outside the pressure hull. All sub- 

 mersibles have one or more thru-hull pene- 

 trations which serve as: Personnel access 

 hatches, viewports, and hydraulic, electric, 

 and mechanical penetrations. 



If such openings are small in comparison 

 to the pressure hull dimensions, the stress 

 level in the area adjacent to the opening is 

 not significantly altered. If the opening is 

 comparatively large, as are hatches and 

 viewports, reinforcement of the area immedi- 

 ately adjacent to the opening is required 

 (Fig. 5.11). In general a tapered reinforce- 

 ment is used, especially for viewport pene- 

 trations. Such reinforcement can be of con- 

 siderable thickness; for example, TRIESTE'S 

 Terni sphere ran from a thickness of 3.5 

 inches to 6 inches around the viewports. 

 Stresses around viewports have been studied 

 and results for the ALVIN viewports are 

 presented in reference (20). In the case of 

 hatches, it is possible to machine both hatch 

 and hull mating surfaces to ensure that the 

 hatch acts as an integral part of the hull and 

 thereby minimizes the thickness of the rein- 

 forcement (21); for this reason no reinforce- 

 ments are seen around TRIESTE'S access 

 hatch. 



The majority of penetrations in cylindrical 

 pressure hulls are found in the endcap hemi- 

 spheres, the reason being that most of the 

 external equipment is located adjacent to 

 the enclosures. When large penetrations are 

 required and present major structural dis- 

 continuities, such as the intersection of two 

 spheres or two cylinders, the designer must 



employ generalized structural analysis com- 

 puter programs, i.e., finite element or finite 

 difference, to determine the configuration 

 and size of the reinforcement. A final verifi- 

 cation of the stress magnitude and displace- 

 ment is obtained by placing the entire hull in 

 a chamber where the pressure is raised to 

 various levels and measuring the values ex- 

 perimentally. However, large submersibles 

 of the BEIS FRANKLIN variety are too large 

 for this procedure; hence, experimental 

 stress verification data is obtained during 

 the submersible's sea trials. A standard rule 

 of the ASME Pressure Vessel Code for exter- 

 nally pressurized structures is that the rein- 

 forcement shall consist of 100 percent of the 

 material taken from the hull. For example, if 

 2-inch-diameter pipe is to pass through a 1- 

 inch-thick hull, then the 3.14 cubic inches of 

 material must be replaced as reinforcement 



GLASS 



GASKET 



METAL 



Fig. 5.10 Cross section of glass to metal joint. [From Ref, (19H 



255 



