neoprene bearing 



gasfcet 



steel compliant 

 retaining flange 



neoprene bearing 

 gasket 



Several sealing systems 

 were considered for sealing the 

 beveled hatch ring to the beveled 

 bearing surfaces of the acrylic 

 plastic capsule. Besides standard 

 O-ring seals, rubber gaskets and 

 epoxy adhesive were also consid- 

 ered. The O-ring seal was known 

 to be reliable, but the groove in 

 the metal would cause a contact 

 stress raiser on the acrylic plastic 

 bearing surface. A rubber gasket 

 interposed between the metal and 

 the acrylic plastic bearing surfaces 

 would eliminate any stress concen- 

 trations, but would permit larger 

 relative motion between the insert 

 ring and the hull. Unless consider- 

 able force was constantly pressing 

 the insert ring against the acrylic 

 plastic, leakage would take place 

 at the beginning of the dive until 

 the capsule reached a substantial 

 depth where hydrostatic pressure 

 force would seal the hatch assem- 

 bly against the acrylic plastic 

 bearing surface. 



Some thought was also 

 given to using epoxy adhesive to 

 bond the hatch insert ring in place 

 permanently, thus eliminating 

 both relative movement between 

 the parts and the leakage. This approach, however, was discarded as it was 

 known that the magnitudes of forces acting across the metal— acrylic plastic 

 interface would be so large that the adhesive would shear, permitting the 

 water to leak in. Although the advantages and disadvantages of the O-ring 

 and the gasket sealing systems are about equal, the O-ring system was chosen 

 for the acrylic plastic capsule because it utilized primarily off-the-shelf seals. 

 If the stress raiser problem proved troublesome later, the lubber gasket system 

 could be substituted. 



Bottom Plate Closure 



Figure 4. Hatch concept chosen for 

 incorporation in the acrylic 

 plastic capsule for the NEMO 

 system. 



