An "O" ring groove was machined in the 

 forward flange to hold a 9-mm-diameter neo- 

 prene ring which provides a watertight seal 

 at low pressure. Metal-to-metal contact of 

 the flanges during deep submergence serves 

 as a high pressure seal. BEN FRANKLIN 

 was bolted together to accommodate future 

 plans for a diver lock-out module which could 

 replace the original aft section. The finished 

 hull prior to bolting is shown in Figure 5.5. 



Bolting: 



Where the pressure hull material is essen- 

 tially non-weldable it may be bolted to- 

 gether. ALUMINAUT serves as an example. 

 ALUMINAUT's pressure hull (Fig. 5.7) is com- 

 posed of 11 cylinders and 2 hemispherical 

 endcaps. Thirteen huge aluminum ingots 

 (17,000 lb each) were cast as rectangles and 

 then heated and forged under hydraulic 

 presses into a cylindrical shape. The centers 

 were then punched out and the partially 

 shaped pieces transferred to a ring rolling- 

 machine and rolled to their final contour; 

 these and the endcaps were later machined 



to critical tolerances of 32-microinch finish 

 on all joint faces (17). The pieces, after sand- 

 blasting, received four coats of different col- 

 ored polyurethane paint 0.002-inch thick to 

 show surface scratches. Flanges were then 

 bolted to each cylinder and then bolted to- 

 gether. The selection of bolts and the bolting 

 procedures were practically laboratory con- 

 trolled. After initial jig drilling, bolt holes 

 were reamed to tolerances of 0.0005 inch or 

 better in roundness and 0.001 inch for size. 

 Some 400 bolts are used in the hull; each bolt 

 and bolt hole was measured individually and 

 matched to each other for the best fit. Each 

 bolt was then shrink-fitted by cooling it in 

 liquid nitrogen at — 320°F prior to insertion 

 and allowed to expand to a degree where no 

 bolt diameter exceeded hole diameter by 

 more than twelve ten-thousandths of an inch. 

 In this case, there was no intention of later 

 unbolting sections as with BEN FRANKLIN. 



Adhesive: 



On plastic-hulled vehicles neither bolting 

 nor welding is feasible; hence, an adhesive or 



Fig. 5.7 ALUMfNAUTs pressure hull (Reynolds Submarine Services) 



253 



