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Re: [PSUBS-MAILIST] External vs Internal Stiffners
A design I am working on employs a combination of internal and external
stiffeners. All of the heavy stiffeners (which reduce effective length for
buckling calcs) are external, so they don't impinge on available internal space
too much, while the rest of the standard stiffeners are internal. This provides
mount points on both sides. This is also a fast boat (~12 kts submerged) so I
have a hydrodynamic outer hull (thin plate - just strong enough to withstand
anticipated impact loads during normal use) attached to the outside of the heavy
stiffeners, with piping, tanks and so forth in between the two hulls. All
spaces are accessible for inspection (outer hull pieces are removeable). Full
penetration, profile ground and stress relieved welds on the external
stiffeners. On the internal ones, on the inside, the shallower internal
stiffeners provide depth for hull insulation, piping and equipment so the
effective internal space of the sub is that of the stiffener internal diameter.
The welds on the internal stiffeners are not under load as with the outside,
but I prefer full penetration welds (so internal stiffeners are also T-section)
in order to avoid creating initiation sites for fatigue failures, given that
this pressure hull has a relatively long design life.
-Sean
Quoting vbra676539@aol.com:
> I'm sorry kids, but when someone says "the only difference is a slight..."
> they are telling me that they've never been there banging their heads and
> bruising their shoulders on internal ribs in a narrow space. External ribs
> are a GREAT thing, given the opportunity. They are more difficult, as they
> have to be full penetration welded as the stresses at depth put the ribs in
> tension, rather than compression. You pay in the shop for benefits in the
> sea. It's worth the time on really small boats (36" to 48" for instance).
> Even a 54" hull with internal rings will give you knots on your head. As for
> the calculations, I'm not an engineer, I'm a pilot, and had the bruises to
> prove it.
>
> And the external smoothness of a walking pace boat simply don't matter, from
> my experience. That's more aesthetics than anything. Once you hang air
> bottles and ballast tanks out there, then a little streamlining fore and aft
> just to ease the water flow is about all you need. If that.
>
> Vance
>
>
> -----Original Message-----
> From: irox@ix.netcom.com
> To: personal_submersibles@psubs.org
> Sent: Wed, 25 Oct 2006 6:58 PM
> Subject: Re: [PSUBS-MAILIST] External vs Internal Stiffners
>
>
>
> It's been a while since I've done any pressure hull calculations, but as far
> as
> the math goes, there shouldn't be any difference between internal and
> external
> stiffeners.
>
> From a construction point of view external stiffeners will be a lot harder.
> The
> weld has to be load bearing (for internal stiffeners, the welds just need to
>
> keep
> the stiffeners in place). Also, external stiffeners will not help push the
> cylinder
> "into round" (since they will all come slightly out of round), so any out of
>
> roundness
> will have to be "fixed" before attaching the stiffeners. The only benifits
> you
> get
> are a slight more internal space, and plenty of points to mount external
> equipment.
>
> Using internal stiffeners appear to be much more simpler, construction wise.
>
> Ian.
>
>
> -----Original Message-----
> >From: DJACKSON99@aol.com
> >Sent: Oct 25, 2006 2:43 PM
> >To: personal_submersibles@psubs.org
> >Subject: Re: [PSUBS-MAILIST] External vs Internal Stiffners
> >
> >Thanks Brian. So who thinks it is ok to use the
> >ABS_Hull_Calculation___Rev_12_17_2004.xls spread sheet without changes but
> actually place the stifferners
> >on the outside of the hull
> >
> >--Doug J
> >
> >
> >In a message dated 10/25/2006 10:46:39 AM Central Daylight Time,
> >ojaivalleybeefarm@dslextreme.com writes:
> >Doug,
> > I found this one, but his question was never really answerd:
> >To: personal_submersibles@psubs.org
> >Subject: External stiffeners, paint, 'exotic' metals?
> >From: Nathanael Henderson <jude@pconline.com>
> >Date: Sun, 28 Mar 1999 10:05:42 -0600 (CST)
> >In-Reply-To: <file:///D:/html/archive/9903/msg00277.html>
> >
> > It appears most subs have internal stiffening T beams, but I see a
> >number of references to external ones as well. External beams certainly
> >have their appeal from the standpoint of internal space (and even some
> >ease of construction). BUT, what do you do after putting on external
> >stiffeners? How do you restore the hydrodynamic body shape to escape the
> >drag of exposed beams? Putting on a second thin hull (perhaps with
> >internal ballast tanks, etc.) seems like the inevitable thing to do, but
> >then how would you maintain/rust proof the inner hull?
> > Along those lines, is there any advice on how to treat the hull? A
> >special type of paint? Anybody up to hot-dip galvanizing a whole sub? :-)
> >
> >
> > Materials. Steel is cheap and easily worked, but what about aluminum
> >and titanium? Aluminum would sacrafice some strength, but for a person
> >with money titanium seems like the gold standard for submarine material.
> >Besides the strength of titanium, it's almost complete invulnerability to
> >corrosion makes it a very appealing material. Anybody know what
> >titanium costs in bulk and if it's unreasonably hard to work? (The last
> >time I saw a price on titanium it was about $30 a pound, but that was for
> >wire, not plate/beam.)
> >
> >
> >Brian
> >
> >
> >
> >
> >
> >----- Original Message -----
> >From: DJACKSON99@aol.com
> >To: personal_submersibles@psubs.org
> >Sent: Tuesday, October 24, 2006 22:19
> >Subject: [PSUBS-MAILIST] External vs Internal Stiffners
> >
> >
> >I remember a thread about External Vs Internal Stiffeners but I can't find
> it
> >in the archive. Can someone please point me to the date or title of that
> >thread? Thanks --Doug J
>
>
>
>
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