tors should be mentioned: entry configura- 

 tion, hull fastening methods, hull sealing 

 methods and hull insert types. 



Penetrator Entry: 



Cable can enter the hull vertically (Fig. 

 7.17a), or at any angle from vertical to hori- 

 zontal (Fig 7.17c). The horizontal entry pro- 

 vides the most advantages because the ca- 

 bles can be supported and protected more 

 easily. 



Hull Fastening Methods: 



Several methods exist to secure penetra- 

 tors to the pressure hull (Fig. 7.23). Briefly, 

 the following comments can be made for each 

 approach: 



a) Bolted Flange — Bolting directly to hull 

 may produce a stress concentration 

 area; the flange consumes a large sur- 

 face area outside the hull and may also 

 cause crevice (and other) corrosion prob- 

 lems. 



b) Internal Lock-Nut — The most widely used 

 method, it provides the least problems. 



c) Welding — This conserves space but is per- 

 manent and, therefore, hampers re- 



placement for maintenance. Also, some 

 hull materials are not weldable. 



d) Adhesives — These have a low confidence 

 level at present. 



e) Direct Screwing — This poses machining 

 and stress concentration problems. 



Hull Sealing: (Fig. 7.24) 



In this respect replacement or removal of 

 the penetrator for inspection is a general 

 requirement. Therefore, welding or adhe- 

 sives are precluded. 



a) Flat-Gasket — This requires periodic re- 

 pressurization. 



b) O-rings — These provide excellent low 

 pressure seals, most widely used. 



C) Metal-to-Metal Tapered Seal — An eighty per- 

 cent metal-to-metal contact is desired 

 and very precise machining is required. 



Hull Insert Types: 



The basic insert types are shown in Figure 

 7.25. Threaded, tapered and conical inserts 

 are found in most submersibles. In the conical 

 insert a plastic gasket is pressurized into the 

 cone area by tightening an inboard lock-nut. 

 Stepped hole inserts create stress concentra- 



BOLTED 

 FLANGE 



h^ 



y SEAL RING 

 ^ LOCK NUT 



INTERNAL 

 LOCK NUT 



C 



ADHESIVE 

 FASTENING 



BONDING 

 'COMPOUND 



FLAT GASKET 



^^^ 



7 



1 



3 



/ 



Direct 

 Screwing 



\ STRAIGHT 

 THREAD 



r^TT^ 



^TAPERED 

 THREAD 



Fig. 7.23 Penetrator to hull fastening methods. 



Fig, 7,24 Penetrator to hull sealing methods. 



344 



