[PSUBS-MAILIST] External Stiffeners

[via Personal_Submersibles]

Sean,


Thanks for that. It just never occurred to me that you could actually get enough penetration (without excessive warpage) to qualify. And it seems not. My doubler plate analogy notwithstanding, of course. I was thinking back to the old days when Perry used doublers. ABS put the kibosh on that, and it was a big change to install doubled thicknesses (for lift pads, for instance). We ground a few old doublers down on a couple of bells and found (surprise, surprise) rust.


Vance



-----Original Message-----
From: Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sat, Apr 26, 2014 8:42 pm
Subject: Re: [PSUBS-MAILIST] External Stiffeners


They are both permissible, provided that the stiffener section is
symmetrical, and the web to hull weld is full penetration.  Vance refers
to a "doubler plate" which is typically a reinforcement joined by
perimeter welding only, which would be prohibited.  Any partial
penetration weld joint creates an artificial crack at the interface
which can precipitate a failure.  All of your pressure boundary welds
must be full-penetration and 100% NDT inspected for defects.  With a
thick section like the posted example against the hull, you can see how
the acceptable technique would be difficult to accomplish, both to first
create the fully fused full-penetration weld and then to do your
subsequent 100% NDT inspection.  The amount of heat you would drive into
the hull cylinder when welding the thick version is also apt to cause
more warpage / shrinkage of the joint than welding the narrow version.
Additionally, the purpose of the stiffener at all is to increase the
area moment of inertia of the combined hull / stiffener section, which
the version with the flange / outstand AWAY from the hull does more
effectively (more efficiently for the same weight of material), in
addition to being simpler to properly fabricate and inspect.

Sean



On 2014-04-26 15:02, Pete Niedermayr via Personal_Submersibles wrote:
> I have been looking at external stiffeners and I see that the figures in the 
ABS Hull Calculator shows them as (see Hull B pdf ) where as some subs (Curasub 
and Aquarius) seem to have them as (see Hull B pdf). Are they both correct ?
>
> Thanks Pete
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