Only one submersible is known with wood 

 as a pressure hull material, the Helle SUB- 

 MAISAUT. Stachiw (14) reported tests at the 

 U.S. Naval Civil Engineering Laboratory 

 with mahogany plywood cylinders and, by 

 virtue of its low density (0.016 lb/in.) and a 

 strength to weight ratio better than that of 

 hot or cold rolled low carbon steels, found it 

 to be quite suitable for depths less than 2,000 

 feet. Remarking on its low cost and easy 

 workability, Stachiw recommends it as a can- 

 didate material for individuals or institu- 

 tions where limited construction budgets 

 prevail. 



An equally promising, and unexpected, ma- 

 terial is concrete (Fig. 5.4). Using an espe- 

 cially formulated concrete mix, Stachiw (15) 

 tested 16-inch-diameter, 1-inch-thick con- 

 crete spheres, with no reinforcement, to de- 

 struction and subjected them to long-term 

 pressure. Two hemispheres were joined with 

 8288-A Epocast furane epoxy after curing for 

 1 month in a 100 percent humidity room. One 

 puzzling aspect of the tests was that while 

 permeability of the concrete to seawater was 

 low (5 ml/hr at 1,500 psi), the salinity of the 

 water inside the sphere was less than that 

 outside. Although more testing is required to 

 man-rate such materials, Stachiw recom- 

 mends its use for fixed installations to 3,500 

 feet where positive buoyancy is required. 



to control moisture content which could gen- 

 erate nascent hydrogen in the weld and 

 thereby weaken it. The U.S. Navy has estab- 

 lished MILSPECS which govern welding ma- 

 terial and the storage thereof. The American 

 Society of Mechanical Engineers has defined 

 requirements for welding of various pressure 

 vessels for use by the commercial sector. 



Similarly, both groups have requirements 

 and tests which the welder must pass and 

 efficiency levels he must maintain. Such 

 tests include welding in different positions 

 such as downhand and overhand, and sub- 

 jecting the welds to various bending, pulling 

 and impact tests, as well as to X-ray and 

 ultrasonic inspection. In the case of BEN 

 FRANKLIN, a dye penetrant system served 

 as an additional test of the welders' effi- 

 ciency (16). 



Fabrication of the BEN FRANKLIN hull 

 (Fig. 5.5) employed both welding and bolting 

 techniques, and the checks and treatment 

 during fabrication incorporated the majority 

 of procedures followed in all steel-hulled ve- 

 hicles. Two European steels, Aldur (77,800 



FABRICATION 



The joining together of the pressure hull 

 components — hemisphere-to-hemisphere cyl- 

 inder-to-endcap, etc. — has been accomplished 

 in several ways: Welding, bolting, adhesive 

 bonding, clamping, and retaining rings. 

 Though relatively straight-forward in a 

 metal-to-metal bond, the problem becomes 

 quite complex with bonds such as glass-to- 

 metal. 



Welding: 



The majority of submersible pressure hulls 

 are joined together by welding; both the 

 welding material's physical properties and 

 the welder himself are governed by well- 

 defined military or civil (commercial) regula- 

 tions. The welding material should be the 

 equivalent of the parent (pressure hull) ma- 

 terial and stored under exacting conditions 



Fig 5 4 Short cylindrical concrete hull shown prior to epoxy bonding of hemisphere 

 caps onto cylinder section (NCEL) 



250 



