(a) Equatorial hatch. 



(b) Polar hatch. 



Figure 3. Basic approaches for providing access to the interior of a spherical 

 acrylic plastic capsule. 



Since a metal hatch system constitutes a serious mismatch of rigidity 

 with the acrylic plastic hull, a concentrated effort was made to reduce the thick- 

 ness of the metal hatch to a minimum, so that the mismatch and resulting stress 

 raiser effect could be minimized. The engineering decision was to reduce the 

 thickness of the metal hatch to the minimum value corresponding in strength 

 to implosion pressure of the acrylic plastic hull. 



One of the problems facing the designer in providing a metal hatch for 

 the capsule was to find a means for firmly attaching the beveled metal hatch 

 insert ring to the acrylic plastic hull so that the whole hatch assembly would 

 not fall out when the capsule was tossed around on the ocean surface. An inge- 

 nious solution was found: secure the hatch insert ring to the acrylic plastic hull 

 by means of a metal retainer flange located on the interior of the hull to which 

 the hatch insert ring would be bolted. Direct contact between the metal 

 retainer flange and the acrylic plastic hull was considered undesirable as it 

 would lead to scoring of the acrylic plastic, and local stress concentrations 

 when the curvature of the capsule decreased during hydrostatic loading. To 

 forestall these conditions, a compliant rubber gasket would be interposed 

 between the metal retaining flange and the acrylic plastic hull. In addition, 

 the retaining flange would be provided with a convex spherical surface 

 matching the concave interior curvature of the capsule. The flange cross- 

 section was to decrease towards its outer edge to make the flange more 

 compliant at the outer edge than at the inner edge at the bolt circle. 



12 



