[PSUBS-MAILIST] viewport questions
via Personal_Submersibles
personal_submersibles at psubs.org
Tue Oct 28 18:38:09 EDT 2014
Vance,
Is the problem with Rain-X a function of interaction with sunlight, salt
water, or ...? I recall about forty years ago there was a paste available
for use on Plexiglas aircraft windscreens, but I was reluctant to risk using
it for fear of doing it wrong and fogging up the windscreen. It was
basically a rubbing compound. Covering the windscreen when stored outdoors to
protect it from the sun was well worth it to retard crazing and yellowing.
Jim T.
In a message dated 10/28/2014 5:12:57 P.M. Central Daylight Time,
personal_submersibles at psubs.org writes:
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_ (mailto: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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