Re: [PSUBS-MAILIST] Design depth

[MerlinSub@t-online.de]

Sonetimes psubers comes sometimes with really shallow diver. For this vessels factor 2 is to low. 

A Vessel with a opertional depth of 10 feet or shall be have a higher figure than 20 feet crush.. 

"Alan James" <alanjames@xtra.co.nz> schrieb:
> Thanks Phil,
> That makes a lot of sense. The test at 1.5 above rated depth & the 100%
> safety margin seem good figures to adopt.
> Regards Alan
>   ----- Original Message ----- 
>   From: Phil Nuytten
>   To: personal_submersibles@psubs.org
>   Sent: Saturday, December 11, 2010 1:21 PM
>   Subject: Re: [PSUBS-MAILIST] Design depth
> 
> 
>   All:
>   We class with lloyds,Germanischer Lloyd and ABS. The only difference in design depth/hull test,etc., that I'm aware of, Is the 
> test depth versus rated depth (or 'working depth') Lloyds Surveyors, for example' is that physical test depth must be  1.4. rated 
> depth - G.L.is 1.5 and so on. Design collapse in all these agencies is 2 times rated or working depth - or,100 percent safety 
> factor. For clarity, the Deepworkers are 2000 foot rated or working depth, 2800 foot test depth and design collapse (as shown by 
> calculation and FEA's) meets or exceeds 4000 feet.
>   Seems pretty easy to me!
>   Phil
> 
>   Sent from my iPhone
> 
>   On 2010-12-10, at 11:25 AM, vbra676539@aol.com wrote:
> 
> 
>     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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