Re: How catastrophic is catastrophic?

[DaveIrons@aol.com]

Rick Ed and all

Judging from the photographs, I've seen, of concrete pressure hulls
that have been tested to failure.  When concrete hulls fail under
pressure a large section suddenly implodes.  However, if you test a
steel hull to implosion the results may be just as catastrophic.  

Concrete hulls have more compressive strength than steel.  The
crush depth of a concrete hull would be about twice that of a steel
hull. 

The possibility of a concrete hull collapsing at depth is seems
highly unlikely.  Stachiw estimates that operational depth is about
3,000 feet.  For a sport submarine in maximum 200 feet of water
that is at least a 15 to 1 safety ratio.  Unlike a steel hull, the cost of
building a 3,000 foot concrete pressure hull is reasonable. 

The maximum safe depth, would be depth rating of the fittings.  I
think the viewport would be the limiting factor.  The acrylic
viewport would probably crack long before the concrete pressure
hull would show any signs of stress.  

A more likely mode failure would be damage on the surface. 
Damage to the hull would be visible as a crack. 

David Irons