size. A new. lower cost foam has also been developed, but research is 

 continuing to further reduce foam costs. 



A number of materials are being tested for use by the USN in 

 submersible hulls and undersea structures. One of these materials, 

 graphite-epoxy, because of its high-strength, low-weight properties, 

 offers the potential for extending operating-depth capabilities without 

 significant payload sacrifice. In a project to evaluate the capacity of 

 graphite-epoxy structures to meet deep-sea requirements, especially 

 built cylindrical models with a SVz-inch-outside diameter were hy- 

 drostatically tested at the Naval Underwater Systems Center. These 

 models satisfactorily met the test pressure requirements, and therefore, 

 newer models with larger diameters are now being fabricated and tested. 



Although acrylic plastic spherical shell sectors have been widely used 

 for manned submersible windows, they have not been found adequate 

 for precision optical systems because they are subject to large displace- 

 ment and deformation under high hydrostatic pressure. Experiments 

 have, therefore, been undertaken to test shell sectors with 150° spherical 

 angles, fabricated from optical glass, chemically surface-compressed 

 glass or transparent cermaic. The tests indicate that a submersible 

 system equipped with a 150° spherical shell window flange assembly 

 made of a chemically surface-compressed glass or ceramic can operate at 

 any ocean depth. 



A wide variety of concrete pressure-resistant structures can function 

 successfully at 3,000-foot water depths. In an effort to extend these 

 depths, concrete polymer is being studied as an underwater structural 

 material. It has excellent properties for use in ocean environments 

 because of its impermeability to water, high durability, and compressive 

 strength on the order of 20,000 lb psi. The tests show an operational 

 depth range for positively buoyant concrete polymer spheres of 4,000 

 feet. Moreover, even though the cost of polymer-strengthened concrete 

 may be three times that of conventional concrete, the structural mem- 

 bers need be only one-third to one-fifth as large as conventional con- 

 crete members, and the increase in durability reduces maintenance re- 

 quirements, making the product cost-effective. 



The problem of marine fouling on concrete underwater structures has 

 also been investigated. A method has been developed for incorporating 

 toxic chemicals into concrete to protect such structures from the approx- 

 imately 2,000 species of marine foulants. Tests indicate that the antifoul- 

 ing concrete is sufficiently strong for construction in which a com- 

 pressive strength of 3.500 lb psi is acceptable. 



Several years ago the USN installed a new titanium alloy hull on the 

 submersible Alvin. This hull extended Aivin's working depth from 6.000 

 to 12,000 feet. Data on the performance of this hull continue to be col- 

 lected for use in the further application of titanium alloys to submersible 



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