Hi Denny

 

Designed to "50% of it's design limit" was because in compression, we found that the submarine could do repeated cycles at that without undue fatigue whereas taking it closer to 100% of it's designed limit would cause sudden and unexpected failure on the next cycle.  For example, we did a bunch of models and pressure tested them before we built the real subs.  We frequently had pressure hull models that were actually stronger than calculated.  When we took these outwardly perfect submarine hulls that had been taken down to the design limit (1000 meters) and tested them again, they failed at about 10% of their design limit.  So while the hull had withstood the compression for a single cycle, once eased from that load, micro fracturing occured and hull collapsed when re-pressurized for a second cycle.  So while both "Deep Flight I and II" are designed to operate at 1000 meters, they could actually double that once.  This also illustrates the difference between steel and composites.  For a steel hull to be certificated to a depth, it has to taken to twice it's designed depth.  So for a steel hull designed for 1000 meters, it must go down once to 2000 meters.  And if it survives, it should be fine since metals generally have no problems taken close to their compressive limits.  For a fiberglass sub to be certified to 1000 meters, it would also have to be tested to 2000 meters but that means that it would have be designed to withstand to 4000 meters so the certification is a problem, (neither Deep Flight isn't certified).

 

Dan