[PSUBS-MAILIST] bolt on rings

Fri Nov 11 11:15:27 EST 2016

Sean you can of course do for example a hatch which close the hole and fill 
the gap..

We make it exact that way on Sgt.Peppers.
The tolerance of the hatch bars was just 1/10 of a milimeter. and if closed 
and under outside pressure
it close the pressure hull cylinder again - even it was made from aluminium 
and not steel as the rest of the hull.
Under pressure this hatch is blocked mechanical by the outside pressure 
which press the cylinder of the shell
close to the hatch bars and not just the hatch from the top.
But the stress calculation to do so was done on a F&E Analysis Computer 
model.

vbr Carsten  

-----Original-Nachricht-----
Betreff: Re: [PSUBS-MAILIST] bolt on rings
Datum: 2016-11-11T15:50:56+0100
Von: "Sean T. Stevenson via Personal_Submersibles" 
<personal_submersibles at psubs.org>
An: "Personal Submersibles General Discussion" 
<personal_submersibles at psubs.org>

I will preface these comments with a standard disclaimer that what works 
and what is explicitly permitted by the rules may not be entirely 
congruent.
That said, when you cut any opening in your pressure hull, you ordinarily 
must reinforce the opening with additional material, in order to carry the 
additional shell stress which can no longer be carried by the material that 
would have been in the opening. Certainly this is the case for window 
openings, because an acrylic window is structurally insufficient to carry 
the anticipated hoop stresses. Where the opening is to be filled with 
material equal or greater in strength than the hull shell material, it is 
less clear cut. We had a discussion some time ago about essentially 
replacing the cutout shell with an equivalent load path through a 
substantial hatch, and there is no reason why this shouldn't be 
permissible, provided the "shell" which is integral to your hatch provides 
an uninterrupted load path. In the case of a spherical pressure hull, this 
means that the hatch "shell" would need to be of equal or lesser inner 
radius than the hull, of equal or greater ou! ter radius than the hull, be 
appropriately centered on the adjoining shell at the interface, and that 
the interface itself be exactly normal to the spherical surface, so the 
angle passes through the centre of curvature and hoop stresses do not 
induce bending.  Any elastomeric seal would have to be positioned outside 
of the theoretical "shell", so that you retain full bearing area in the 
metal to metal interface. You would also have to ensure that the hatch 
itself is appropriately reinforced if you have penetrations for windows or 
dogging mechanisms in it.  What you would not be able to get away with is a 
hatch which sat substantially proud of the neutral axis within the hull 
shell (i.e. a "lid" on top), as that would provided no structural support, 
and thus would require the same reinforcement around the hole, integral to 
the hull shell wall, that would be required for a window or other non 
structural penetration.
Apart from that, I imagine that a hatch seat similar to the recommended 
methods for penetrating "Nemo" windows, as outlined in PVHO-1 and Stachiw's 
book, would prove adequate. You will note that in no instance do these 
methods permit screwing or bolting to the acrylic hull shell, and I am of 
the same mind with regard to a metal shell. Whatever you come up with, you 
can bolt two halves of an insert to each other across a hole, but must 
avoid drilling into your base hull shell, or indeed removing material from 
it for other purposes if not adding material to compensate, or if you 
already have excess shell thickness, or are prepared to derate the hull. 
Instead of machining sealing features on the hull, I would look at using an 
adhesive sealant to seal to your designed insert (which must already be 
structurally seated against the hull opening), and restrict the o-ring 
features to the insert and hatch exclusively.
As for sealing two hemispheres together with an o-ring seal, there's no 
reason that you can't do that, but you need to pay attention to centering / 
concentricity, and of course your design o-ring gaps / extrusion 
considerations, etc. I would probably be inclined to simply face the 
hemispheres, and employ a double sided seat ring which would incorporate 
the sealing features, or attach a ring to each hemisphere with an adhesive 
sealant, and have the rings seal to each other, in which case you could 
also incorporate assembly / centering features into the rings so that they 
consistently seat in the correct position.  While not strictly required (a 
seal ring between two hemispheres is functionally a short cylindrical 
section), I might give consideration to facing the hemispheres slightly 
short to account for the ring length, such that in the fully assembled and 
seated condition the hemispheres remain concentric and there is no jog in 
the load path through the se! aling ring(s).
Hope that helps.
Sean

On November 10, 2016 6:51:51 PM MST, hank pronk via Personal_Submersibles 
<personal_submersibles at psubs.org> wrote:
  Sean, I know we talked a bit about this idea before but I need a
  refresher.  Can I machine a hole in a heavy sphere and insert a hatch
  land\reinforcing ring assembly that bolts to the sphere.  It looks like
  Karl Stanley may have done that with his front dome.  This idea if
  feasible makes building a deep diver more realistic.  I am thinking  of
  trying this on my current sphere just to see if I can do it.  Better to
  screw up a cheap sphere first.  ;-)

  Next question, when I look at the Deep Rover sub, it has two
  hemispherical domes coming together on a two sided land.  I am sure the
  land also gives the dome! s side support.  Why would this design not work
  with two heavy steel hemispherical domes.  I am talking 3 to 4 inches
  thick.   The  steel domes can easily be machined with a flat land and
  o-ring grooves.  The idea is to eliminate a very costly weld and it would
  be pretty darn nice to build with the top half of the hull removed.  
  Hank

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