[PSUBS-MAILIST] New submarine

[Jon Wallace]

As far as I'm aware, ABS doesn't deal with crush depth only maximum 
working pressure which incorporates usage factors (n), in this case of 
n=.67.  If n=1 could be considered "crush depth", then the calculator 
shows crush occurring at 2287 psi with 1.5 inch thick hemisphere and max 
working depth of 1532 psi with a usage factor of n=.67 which is right in 
the parameters that he is looking for.  The problem with using n=1 as an 
indicator of crush depth, I believe, is that there's no way to guarantee 
it's an accurate representation of when the hull will fail because 
actual fabrication variables resulting in less than ideal geometric 
structures can lower the calculated result.  When using ABS/ASME we 
should always be solving for max working pressure, not crush depth.

So your observation is correct, and solving for a working depth of ~3000 
feet results in a much thinner hemisphere.  I didn't know what Scott was 
using for a safety factor so just plugged the numbers to get 2578 psi 
from the ABS calculator, but that obviously is over-built for what 
Scott's intended use is.  Using a thickness of 1.25 inches, ABS is 
showing max working pressure of 1268 psi or 2849 feet, just slightly 
less than his 3000 foot requirement.

Jon


On 4/9/2014 10:08 PM, Alan James wrote:
> I'm a bit confused Jon,
> Scott was asking for the thickness for a crush depth of 5709 feet 
> (2543 psi).
> You are saying 2.5 for a maximum working pressure of 2578 psi. The 
> working pressure
> I thought was the design depth or maximum operating depth.
> Alan
>

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