[PSUBS-MAILIST] viewport questions

Tue Oct 28 18:12:17 EDT 2014

Jim,
It seems to me that Rain-X and acrylic aren't the best of friends. I've never used it, anyway. As a point of interest, we had the secondary shields on all the Perry boats originally, but with 3/4" holes top, middle and bottom, which left room to stick a hose in for rinsing. and the holes pretty much disappeared in the water and weren't a problem, visually. I think they used a couple of dozen screws to put them on, so we didn't do it very often, as you might well imagine.
Vance

-----Original Message-----
From: via Personal_Submersibles <personal_submersibles at psubs.org>
To: personal_submersibles <personal_submersibles at psubs.org>
Sent: Tue, Oct 28, 2014 6:01 pm
Subject: Re: [PSUBS-MAILIST] viewport questions

Hi Alec,

What is the average distance between the two domes?  Do you have any type of mesh etc. over the 1/4" holes to keep debris out?  Do you have some type of flushing system for cleaning the surfaces between the two?  Since that's an ambient space I'm guessing it wouldn't take too long to remove the outer dome when you want to do a thorough cleaning.

All:  Have you been using Rain-X on your view ports and domes?  A while back I saw some ads for another hydrophobic product that claims to be superior to Rain-X, but I don't recall the brand.

Best regards,
Jim T.

In a message dated 10/28/2014 4:30:30 P.M. Central Daylight Time, personal_submersibles at psubs.org writes:

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

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