Re: [PSUBS-MAILIST] Design depth

[MerlinSub@t-online.de]

Hi Vance, 

we finalise just the FE-calculations for the Javasub (3+1seater) and the Northsub (3seats). 
Both boats have the same design - Java is just a little longer.

Resulst are crush at 900m (3000 feet), work depth 400 (1300 feet) test at 500 (1600 feet). 
Shell thickness is about a half inch, the first calculation by hand shows crush at 500m 
the difference between the first 500 crush and than later increase crush up to 900 m was a 
optimize process of the stiffteners by the FE method and the fact that the hand method 
is far away from the optimum to find local high force spots. 

Here are the Table fore classification to Germanischer Lloyd: 
dd x factor = td  and  dd x factor2 = cd

design deep   -   test deep    -  crush deep  (all in feet)

  164   x 1,7    279    x 3,2       525  
  328   x 1,4    459    x 2,4       787
  656   x 1,25   820    x 2,0      1312
  984   x 1,2   1180    x 1,87(!)  1840 (1968)
 1312   x 1,2   1574    x 1,80(!)  2361 (2624)
 1640   x 1,2   1968    x 1,76(!)  2886 (3280)
>1968   x 1,2  >2362    x 1,73(!)  3404 (3936)

(!= factor shall be 2,0 if water deep is more than design deep)
  
vbr Carsten


<vbra676539@aol.com> schrieb:
> You guys have fallen head over heels in love with a logic trap, heavily basted with semantics. Give it up. Design depth is your operating depth PLUS the percentage required for testing. It means the depth to which the pressure vessel may be taken repeatedly without incurring irrecoverable damage.
> 
> 
> 125% doesn't make some people happy. I'll just stick in my 2 cents and tell you that I have done a whole bunch of dives in vehicles built and tested to that standard. Crush depth is an arbitrary derivative of the overall calculations, suggesting that all things being perfect, if you go this deep (whatever THIS happens to be) then the hull MAY suffer irreparable damage, and if it does, then THIS is the site of most probable damage. The THIS is typically a measure of the weakest link in the design, which is specific to the design, not general discussion. It is NOT a weak link, but simply the first failure point.
> 
> 
> A C-class Perry for instance would be rated for 1200 feet maximum operating depth. It's design depth (and unmanned test depth) would be 1500 feet and it's crush test.....hmmm, I forget. About 1800 and change, I think. Maybe 19 and change. That kind of thing is in the initial ABS calculation package, if you happen to have it. However, it is not normally in the general ABS certs. I do not have a crush depth number for Gamma, for instance, but do have her certifications.
> 
> 
> For general interest, Nekton Alpha, Beta and Gamma are all rated at 1000 feet and were all tank tested to 1500. Crush depth was ascertained by model testing, which verified the calculations handily (just over 2000 feet). Perry was doing repetitive construction on two proven primary designs (tubular hull, internal or external ring stiffeners). Once proven, in other words, all they had to do was replicate and prove that they had done so.
> 
> 
> As to accepting one safety factor over another, I'd say 125% should be the accepted norm, based on experience and history. Anything over that is a personal choice. I feel one way, somebody else feels another. Potato, potahto.
> 
> 
> Shallow boats are easy to double up on. The old Submaray, for instance, was 3/8" plate and they held it to 300 feet for safety. The PC-8, on the other hand, was also 3/8" plate and I can't even tell you how many times I've been to her operating maximum of 800 feet. Different construction techniques. Different design. Different results.
> 
> 
> Vance
> 
> 
> 
> 
> 
> -----Original Message-----
> From: Jon Wallace <jonw@psubs.org>
> To: personal_submersibles <personal_submersibles@psubs.org>
> Sent: Fri, Dec 10, 2010 4:53 am
> Subject: Re: [PSUBS-MAILIST] Design depth
> 
> 
>               
>     Jim,
>     
>     Design depth is derived from the parameters (material type, hull    thickness, number of ribs, spacing of ribs, etc) used in ABS/ASME    formulas to determine the maximum external pressure that the    submarine can operate in.  I don't think ABS or anyone else can    reliably calculate "fail depth" or "crush depth" because those    depths are highly dependent upon quality of material, fabrication,    vessel use/maintenance, etc.  The crush depth could be some    percentage above or below design depth, however you could only find    out definitively by testing the vessel to destruction.  For that    reason, you don't want to perform a manned dive to 375 feet.  Make    sure that is an unmanned test.  You'll note that ABS Underwater    Vessels Section 3.5 limits the manned test dive to the design depth.
>     
>     Jon
>     
>     
>     On 12/10/2010 9:04 AM, JimToddPsub@aol.com wrote:    
>                           
> Jon,
>         
>  
>         
> I need to read and study the whole ABS            publication thoroughly, but from what I've read is seems            that the Design Depth I would need to claim would be 300            feet.  During the survey I would need to dive in increments            to 375 feet (300 x 1.25).  The vessel would then be rated to            300 feet.  Per ABS, Design Depth is the depth to which the            vessel is "designed and approved to operate."  It's going to            be approved to 300.  If I want to have it approved for            anything more than that, I'll have to have it surveyed to            125% of whatever I want its operating depth to be.
>         
>  
>         
> What is surprising is that [so far] I see            nothing in ABS that specifies how the Design Depth must be            derived.  It seems rather arbitrary rather than stating            something such as "60% of the calculated fail depth."
>         
>  
>         
> Jim
>         
>  
>         
>           
> In a message dated 12/10/2010 1:24:29 A.M. Central            Standard Time, jonw@psubs.org writes:
>           
> A              different approach is to say, I know I don't want to dive              deeper than 300 feet (my max operating depth) and I want a              2x safety margin.  That means using material capable of              withstanding 600 feet depth.  Now with this approach you              certainly may not pass a 1.25 overpressure test for a 600              foot design depth, however you've already self imposed a              2x safety margin.  If you wanted ABS certification, then              you simply claim the design depth as 480 feet.  Now you              meet the ABS requirement (480 x 1.25 = 600) and also are              still well within your 300 foot self-imposed depth limit.
>               
>             
>         
>       
>     
>   
>  
> 




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