[PSUBS-MAILIST] viewport questions

Tue Oct 28 18:00:30 EDT 2014

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_ (mailto: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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