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Originally Posted by LoBlo
We calculated the maximum stress that the structure needed to withstand and then designed the loading points to fail under twice that amount. However, estimation, conservative guessimates and worst case scenario are factored into just about every point in those estimates with the true failure stress of a load point really an unknown. It really is a shot in the dark, but one could probably be reasonable to think that a new sub without any damage could sustain alot more than its crush depth and live to tell about it, like you've already mentioned.
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All you say is truth... Me too thinks that NEW sub can withstand little more... But what you say that nobody really knows what is the real load at which structure fails... If you are designing a bridge, and are not sure if your safe margin is perfectly safe, and are not sure if it REALLY can withstand what numbers say... you just increase the margin. You don't have money to build whole section of a bridge and make destructive test on it anyway...
But you can't make it with submarine, or airplane - just increase the margin to be sure. You have to be quite sure what it can take. So for so important projects like aircrafts and submarines people from time to time test such things just to have idea of what they REALLY can withstand :-), and then base on those tests for some time, and then make new tests while designing new construction... I know that whole sections of submarines were tested for fail pressure when designing really NEW (new designs, new materials) constructions, like when the Russians tested sections (or maybe whole hull?) of first titanium submarine. I could bet that sections of hull from new (HY-100?) steel were tested to fail too... and maybe even material tiring tests - somone someday tested this to know today what limits put on aging sub...
When they build new aircraft today, B-777 or Airbus A380, they know really good what the plane can withstand. I remember an destructive test of wing strength made on whole big passenger airplane airframe. They were bending the wing to the point it failed. This point was, if I remember, around 102% of calculated value... so it was calculated quite precisely :-).
I - personally - wouldn't try do dive a sub below given crush depth, even new one... but of course it's an open question and either of us can be right :-)
Probably it can really withstand some more, if new... but on the other hand, just like you said, even if the hull as a whole take it, one of thousands small thing like opening in the hull or internal pipe that is weaker... and it can kill whole sub and crew... remember the australian Collins accident lately...? They said they were close, very close...
It can happen even on less than crush depth, but while closing and passing crush the probability of such thing increases by factor of ten probably...
About Seawolf speed - yes, it can have much more powerfull reactor, but it is also much bigger than LA. And correct me if I'm wrong, it's not reactor that counts, it's first the steam turbines limit (this is reason that nuclear carriers had same max speed as conventional - they had different steam generators, one conventional, second nuclear, but the turbines were the same and had same output power...) and secondly how much power the propeller can transfer to the water... (but yes, IIRC the LA is rather reactor-limited, all other parts of chain being more capable).
The Alfa and Papa, speed record breaking subs, were just big metal-cooling reactors and machinery monsters with not much place left for other things... SW is normal submarine with much place for weapons, sensors ect. similar like LA class... I really wouldn't expect it to break those records... it can be quite possibly the fastest OPERATIONAL sub in the world (with all Alfas decommisioned long ago), but wouldn't take the words as absolute record breaker...
I think if we have an hydro enginer here, with help of few smart programs like NavCad or it's free analogs, can quite accurately estimate drag of SW hull (or at least difference between LA hull and SW hull) and maybe even the propeller efficiency, although it's a water jet... there are good programs for determining ordinary propeller performance but don't know if for waterjets... In most simple case we could compare drag increase of SW hull to LA hull and compare this with official data of output shaft power, and see what speed could we get... the question is if we can trust the values that are given for SW propulsion...? ;-)