Although the hatch system requires some arrangement for opening 

 and locking the hatch by the occupants of the capsule, no thought was given 

 to this problem during initial planning, because it was thought that any 

 locking arrangement used in submersibles or by the chemical industry in 

 autoclaves would be satisfactory for the NEMO capsule and would have very 

 little if any bearing on the stress distribution in the hatch assembly or in the 

 acrylic plastic hull. 



Penetrations. Penetrations for electrical and hydraulic conduits 

 represented a serious problem as they are sources of serious stress concentra- 

 tions. Rather than have them distributed throughout the pressure hull, as is 

 customary in steel pressure-resistant capsules, they were all placed in a single 

 metal plate insert (Figure 4). This eliminated several design problems. First, 

 a great number of penetrations in an acrylic plastic hull with the accompanying 

 stress concentrations were replaced by a single penetration with a stress con- 

 centration approximately equal to that of the hatch. Second, placing all the 

 penetrations associated with electrical and hydraulic feedthroughs in a metal 

 plate eliminated all problems associated with drilling and tapping acrylic plas- 

 tic. And third, placement of the individual penetrations in the metal plate 

 made the incorporation of reinforcements around the many penetrations a 

 relatively easy problem to solve. This was accomplished by placing the 

 penetrations in a thicker section of the plate, where the effect of stress 

 concentrations would not necessarily initiate failure of the whole plate. 

 The location of the plate itself was optional, depending on other factors 

 like (1) method of attaching the capsule to the submersible'sexostructure 

 and (2) method of attaching the life support, seats, and control console to 

 the capsule. 



The same method of sealing and attaching the penetrator plate to the 

 acrylic plastic hull was to be utilized as for the hatch insert ring. Furthermore, 

 by choosing the same diameter for the penetrator plate as for the hatch insert 

 ring, no additional detail design would be needed for the seal and retaining 

 flange. 



External Attachment of Capsule. The attachment of the capsule to 

 other structural systems posed a difficult problem to which several solutions 

 were considered. The difficulty of attaching the capsule to another structural 

 system lay in several design and operational constraints that had to be satisfied 

 by the proposed attachment method. The design constraints that had to be 

 satisfied were (1) no direct attachment to the acrylic plastic hull by means of 

 steel bolts or screws, (2) no restraint was to be imposed on the decrease of 

 capsule diameter during pressure loading, (3) the attachment was to be stiff 

 enough to prevent excessive movement of the whole capsule with respect to 

 the framework during raising or lowering of the NEMO structure in the ocean, 

 (4) retention of as much panoramic visibility as possible for the capsule even 



14 



