[PSUBS-MAILIST] Fw: Elementary 3000 new paint

[Sean T. Stevenson via Personal_Submersibles]

You probably did well by selecting a 15 degree angle, versus 30, 45 or anything more pronounced. It sounds like you'll have the strength you need. I hadn't thought about the hatch getting stuck - perhaps a jack screw or other means of prying would be a good backup plan?

Sean


On February 13, 2016 9:11:54 PM MST, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Sean,I went with a angle of 15 degrees off vertical on the land, I did
>that thinking if the angle was closer to vertical there would be more
>force generated by the hatch pushing into the land.  This force would
>help support the reinforcing ring against the sphere.  I struggled with
>this because I did not want the angle so close to vertical that the
>hatch could get stuck in the land.  I also kept the reinforcing ring
>high in the sphere so that the bulk of the material was in line with
>the sphere.  I did that so there was not unsupported material at the
>bottom of the ring.  I considered machining the top of the land ring
>smooth with the sphere for continuity but opted to keep the extra
>material for brute strength.  All of this is based entirely on my gut
>feeling.  How is that for an engineering principal. ;-)   Hank 
>
>On Saturday, February 13, 2016 8:12 PM, Sean T. Stevenson via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
>
>That would be true if there were no friction, and if there were no
>forces acting normal to the shell surface; however, such an angle would
>be very slight indeed. In reality, the same pressure that is acting to
>compress the sphere is also acting to press the hatch into the hole,
>and there is friction between the mating surfaces, as well as tension
>from the hatch dogs. As such, the range of interface angles that will
>still allow the hatch to carry the full shell stress is somewhat
>greater. It's a bit of a moot point, since such load carrying ability
>is not relied upon in design, as reinforcement of the shell surrounding
>the hole is required by the rules, but is a thought exercise for true
>optimization of the geometry.Sean
>
>
>On February 13, 2016 7:21:10 PM MST, Private via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>Very interesting, I had not thought of that. Would the cone not just
>have to be angled such that its surface were normal to the outer
>surface of the sphere?
>
>Thanks,
>
>Alec
>
>
>On Feb 13, 2016, at 8:45 PM, Sean T. Stevenson via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> At what angle is the interface? I ask because as the shell compresses,
> that shell stress will act through the interface on the hatch, and at
>some critical angle, will actually act to push the hatch out of the
>hole
> - at least to the extent that the hull shell deflects / gets smaller
> under pressure. This is dependent on both the interface angle, the
>friction between the two mating surfaces, and the strength of your
>hatch
>dogs. Ideally, you want the hatch to lock in place un! der thestress
>and
> provide that continuous load path through the hatch dome, instead of
> being pushed outboard by the deflecting shell. In the latter case, the
> deflection will be minor and probably not represent a sealing problem,
> but it will cause the shell to behave as if it doesn't have that
> continuous load path through the hatch carrying the full shell stress,
> necessitating greater reinforcement around the hole. That said, your
> hatch land may already be sufficient reinforcement - that's why I was
> hoping for a closer look.
> 
> Sean
> 
>
> On 2016-02-13 15:17, hank pronk via Personal_Submersibles wrote:
> Sean,
> Yes the hatch and seat are conical. The hatch dome is in line with the
> hull so the load path is a smooth line. 
> Hank
>
> 
>
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