A large hull penetration, major diameter of 50.25 in. (1275 mm) 

 and minor diameter of 42.4 in. (1075 mm), was located at the apex of 

 each hemisphere. This penetration size was equivalent to 40% of the 

 hemisphere diameter. The design philosophy for the penetrator was to 

 make it stiffer than the concrete material it replaced so that the hemi- 

 sphere was "unaware" of the large hole. The steel penetrator was 

 epoxy-bonded to the concrete, using the surface preparation method 

 described for the joint. 



During the 10-month seafloor construction experiment, an acrylic 

 window assembly was used in one penetrator and a hatch assembly in 

 the other penetrator. The window and hatch were subsequently 

 replaced with steel plates for the implosion test. 



Six penetrations, major diameter of 6 inches (152 mm) and minor 

 diameter of 5 inches (127 mm), were included in one of the hemi- 

 spheres; these penetrations were part of a seal and gasket study. 



Two smaller penetrations, major diameter of 4.5 inches (114 mm) 

 and minor diameter of 4.0 inches (102 mm), were also included near the 

 center of the cylinder section to accommodate pressure rehef valves. 



For the implosion test, three of the small hemisphere penetrators 

 were modified for electrical feed-throughs and pressure ports. The two 

 cylinder penetrations were sealed. 



Additional irregularities in the concrete wall included five feed- 

 through boxes for strain gages mounted on reinforcing bars. These 

 boxes were located on the interior wall and measured 2.5 inches (64 

 mm) deep by 4 inches (102 mm) in diameter. In these areas the local 

 wall thickness was reduced to 7 inches (178 mm). 



Prior to the implosion test, fifteen 3.25-in. (83-mm) diameter cores 

 were drilled from the wall at various locations around the cylinder. 

 Steel plugs were epoxied in the core holes. 



During original assembly, the exterior of the concrete structure 

 was coated with a phenohc waterproofing system. After lightly sand- 

 blasting the concrete, a primer and topcoat (Phenoline no. 300) were 



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