[PSUBS-MAILIST] viewport questions

Tue Oct 28 17:29:59 EDT 2014

Hi Vance,

Actually it starts at 2" thickness, and at the time was the thickest dome
Greg had made. It was an iffy proposition, meaning he didn't know if it
would turn into sub jewelry or just a deformed glob of expensive material.
Luckily it came out virtually perfect.

My hull is 31" OD, a little smaller than yours. The window is a 120 degree
segment, just under 27" OD. So the trick is how to span the gap between the
27 inches and the 31 inches. In the original design, this bow window also
acted as a hatch, a la Deep Flight. I made a massive Al ring 31" OD, which
telescoped on linear bearings and four 1.25" bars, driven by rams. With
ensuing redesign, the need for all that disappeared because I now have a
coning tower, so I've dropped the bars and rams, and the seat is now
mounted to the hull very simply with four big bolts. It will make a very
handy big door into the sub for maintenance purposes, but is overkill and
the window could be mounted by using part of your existing endcap and a
permanently welded conventional seat.

One big decision is the window seat geometry. I like conical because PVHO
rates it for twice the life of square edge, but it requires fabrication
capabilities that Greg didn't have for the window and I didn't have for the
seat. So its a square edge for the simple reason that we could make it that
way.

I should mention the Al ring actually has two domes on it, one inside the
other. The 27" dome is structural, and the outside dome is 31" and only
half an inch thick. The outside one is just for fairing, to protect the
structural dome from abrasion, and to mitigate collision damage. The space
between the two domes is free flooding, and there are 1/4" holes around the
edge of the outer dome to facilitate that. In a collision, the water would
squish out through the little holes, so the thing is basically a shock
absorber.

As for calculations, I will paste the window calcs below. It is really just
table lookups from PVHO tables, a simple cook book. The seat would have to
be calculated with FEA. I didn't have FEA, so I did like the Greeks and
Romans. You know why the Partenon is still standing? Try to do engineering
calculations using Roman numbers! It was too complex, so they simply made
everything massive. The seat is one integral piece of aluminum of
ridiculous proportions, and it backs into a 516 gr 70 ring on the end of
the hull that is an inch thick and two inches deep. I'm pretty confident
that ring isn't going wobbly before something else does.

Best,

Alec

----------------- pasted ------------------
Viewport Depth Rating per PVHO-1a-1997

The following calculations and specifications are for a sperical sector
window with square edge, to include an optional O-ring seal.

1) Determine Conversion Factor (CF)

Water temperature  = 75 °F (tropical conditions)

>From Table 2-2.4, CF = 7

2) Given actual fabricated dimensions

tmin = 1.73”

Di = 26.847”

\t/Di = 0.064

Entering table 2-2.10 with STCP, t/Di = 0.064

Solving for Critical Pressure = 3,460 psi

Since Short Term Critical Pressure (STCP) = CF x P = 3,460 psi

Solving for P,        P = 3,460 / 7 = 494 psi

\ Safe operating depth for window = 1,139 fsw

On Tue, Oct 28, 2014 at 3:48 PM, via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Alec,
>
>  I hope this is still you.
>
>  I've been talking to Greg about a major retro-fit on my K-350--a full
> hull-diameter dome segment viewport in place of the forward elliptical
> head. He mentioned having built yours (the 1000' version) while we were
> talking about thickness and whether to try and use something out of Pete's
> junk pile.
>
>  While we were chewing the fat about this, he said that to the best of
> his recollection, yours started at 1.5" thickness, and that he could build
> it for me (maybe a 150 degree arc segment) for what I thought was a very
> reasonable amount.
>
>  My problem (okay, one of my problems) is that I don't really know how to
> do the calculations for these things. That said, I'm wondering if a partial
> copy of yours might not do the trick for my application (it would be tested
> much shallower, 500 feet or thereabouts).
>
>  I don't know how you feel about sharing that kind of thing, but I have a
> picture in my head of an acrylic bow K-350 with some fairings and a
> Minn-Kota driven Deepworker style propulsion system. I think it would make
> a great little boat, and so if I can get the viewport and frame designed,
> then it's going to be built.
>
>  It's time to play if I'm going to. So, what do you think?
>
>  Best Regards,
> Vance Bradley
>
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
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