[PSUBS-MAILIST] viewport questions

Tue Oct 28 18:04:41 EDT 2014

Thanks Alec,

I'm with you on the window seat, and maybe we can do a little more with that nowadays than when you were building. What I'm planning is a hull diameter port of slightly smaller than hull radius (maybe a chord depth of 12 to 15 inches).

Scratching my head about it, I figured the easiest thing to do was just ditch the forward ellipse entirely and replace it with the port and a diameter matched hull cylinder extension to make up for the difference. The steel portion of the assembly might end up a foot long or so. That way I can build the steel viewport seat on the bench, so to speak, and might (I say MIGHT) be able to weld the assembly back to the hull without distorting the mating surface.

Will have to hear from some welder/machinists about that before I decide. Full penetration welds make a lot of heat, so that part worries me. It would be expensive to true the thing up once all welded fabrication is complete, but I really will need that extra bit of hull length anyway, so it might just come to that.

A second possibility is to weld a mating flange into the hull (flat on the hull side, which would be cheaper to true up, machine shop wise). Then I'd weld a match with o-ring groove on one end of the viewport assembly with, of course, the port on the other end. There would be two big o-rings to deal with (viewport and hull), but that doesn't matter in any practical sense, assuming the fabrication is accurate--and if it ain't, then I did it wrong. 

The weights and balances should work out pretty close, so it will still be a K-350 more or less. Only without the hawk nose main ballast tank out front. The sub will need saddle tanks then, rather than the fore and aft.

Cliff and I are already on the same page for propulsion arrangements, and I've got the pods for a dual 36 volt system plus a couple of 12s for this and that. I doubt that I'll ever be able to match the Redus fiberglas work, but this thing will have to be faired at least somewhat. If all that works out, then I'll use HP air mounted outside, and medical oxygen bottles racked inside. And if my guesstimates work out, then I should come out pretty close to even.

At least that's the plan.

Vance

-----Original Message-----
From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Tue, Oct 28, 2014 5:30 pm
Subject: Re: [PSUBS-MAILIST] viewport questions

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 DepthRating per PVHO-1a-1997

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

1)Determine Conversion Factor (CF) 

Watertemperature  = 75 °F (tropical conditions)

FromTable 2-2.4, CF = 7 

2)Given actual fabricated dimensions

tmin = 1.73”

Di = 26.847”

\t/Di = 0.064

Enteringtable 2-2.10 with STCP, t/Di = 0.064

Solvingfor Critical Pressure = 3,460 psi

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

Solvingfor P,        P = 3,460 / 7 = 494 psi

\ Safe operating depth forwindow = 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

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