these conditions. It is impractical to con- 

 struct the viewport flange or its housing out 

 of the hull itself. For this reason, an insert is 

 separately machined, then forged to the de- 

 sired tapered thickness and subsequently 

 welded into the hull with the insert in place. 

 The inserts are also required to be of mate- 

 rial similar to that of the hull. 



Conical Viewports: From its first inception, 

 the 90 degree conical acrylic plastic viewport 



of Professor Piccard has been the mainstay 

 of deep submersibles. The only reported inci- 

 dent of failure was aboard ASHERAH when 

 it struck an underwater object and cracked 

 its viewport; however, no flooding resulted. 

 Exhaustive testing (26) of plastic viewports 

 of various thicknesses and angles produced 

 sufficient knowledge to recommend dimen- 

 sional constraints and viewport seal design. 

 Figure 5.15 presents typical sealing on past 



RETAINING 

 RING 



VIEWPORT 



\ ^ 



GASKET 



frx^. 



HULL 



(a) Lapped-Joint Seal. 



(b) Gasket Seal. 



^Q_ 



(c) 0-RingSeal No. 1 



Fig. 5.15 Current conical viewport seal designs. [From Ref. (26)] 



261 



(d) 0-ringSeal No. 2. 



