Thank you Rob. my job allows me the time to do alot of reserch in the last few months around an estimated 600 hrs just to pass time and this is the best information I have seen yet that is applicable to prevent people from making fatal mistakes. At one point I was willing to attemt test on this expensive product myself unnecacerally. it
LOL, please excuse the info on my TV at the top of my
email. I was on hold with a warranty issue while
writing it and forgot to delete my scribble notes
before sending the email. ;-)
/Rob
--- Rob Ossian <rob_neptune@yahoo.com> wrote:
> "Panasonic TH-37PWD"
>
>
> I also looked heavily at Polycarbonates (primarily
> Lexan, but a few others as well) when researching my
> sub's design but quickly found that this material
> was
> not a good choice for a viewport. Very disapointing,
> as I had a source lined up for a brand new f16
> canopy
> for less than $1500 that I had hoped to be able to
> modify into a shallow water (<250 feet) 1 atm.
>
> The problem with polycarbonate is in the molecular
> structure of the material and how it reacts when
> stress is put on it. Polycarbonates react to
> stress/pressure by flowing away from the stress
> point,
> which is why they are bullet resistant and used in
> helicopter/jet canopies. When an object travelling
> at
> high velocity hits the poly, the molecules of the
> material react much like the surface of a jello
> cube,
> shifting the energy away from the point of impact in
> order to mainstain integrity. Conversely, the
> molecular structure of acrylic does not share this
> force across itself, as it is a more crystaline
> structure. In the same experiment, acrylic would
> keep
> the force centered on the point of impact, causing
> the
> sample to buckle/fail/chip/fracture.
>
> In terms of submersible viewports, there is a
> tremendous amount of compressive pressure placed
> upon
> the viewports and this causes polycarbonates to
> deform
> as that pressure increases. This means that the
> reliability of Lexan as a viewport material would be
> extremely low at depth, and entirely dependent on
> variables unqie to each dive (specific depth,
> temperature variations, age, wildcards, etc).
>
> Meanwhile the behavior of Acrylic/Plexiglass under
> pressure is well known/tested to be capable (when
> properly manufactured) of maintaining it's cohesive
> structure until it reaches a fairly easily
> predictable
> fail-point. At that fail point, the crystalline
> structure of the acrylic will shatter like glass,
> and
> then the port itself will likely fail
> catastrophically. (<--Think about that word)
>
> I am very frustrated at the apparent high cost of
> Acrylic/Plexiglass, but at present I am not aware of
> any other alternative materials that can be used for
> viewports with any equally high degree of safety or
> confidence. If anyone knows of any, please share!
>
> Hope this info is of some help,
> Rob
>
> --- skrewgun007@aim.com wrote:
>
> > Thank you most helpful. I do need to apologize
> for
> > the fact that I accidentally dropped my sub
> testing
> > under Franks poetic outlook. I read it and used it
> > to send out my message without renaming the
> subject.
> > does anyone else know of any poly test that have
> > been done or have anything else. ohh yea, I asked
> my
> > local glass man how much 1.5" acrylic ran and he
> > told me $24 a square foot. I don't know if he was
> > right since he was guessing. what is a good rate
> on
> > this material and where can I find 2" thick stock
> > for my front view port? any on line suppliers.
> what
> > do you mean to expensive. I figured you guys where
> > made of money LOL just kidding.
> >
> > -----Original Message-----
> > From: empiricus@telus.net
> > To: personal_submersibles@psubs.org
> > Sent: Thu, 5 Oct 2006 2:15 AM
> > Subject: Re: [PSUBS-MAILIST]sinking....
> >
> > Hi there - I brought just that topic up a few
> > months ago about polycarbonate vs. acrylic. Phil
> > Nuytten was kind enough to give his two cents. I'm
> > paraphrasing here. First: Acrylic has been
> > researched to the nth degree and is very
> predictable
> > because of that research. The numbers are out
> there.
> > Second: It is more brittle, however, and in an
> > ambient wet or dry sub my choice would be the
> > polycarbonate simply because of collision, either
> > with a falling anchor or a bump into a reef.
> > Third: Poly under pressure will creep apparently.
> > That makes it unpredictable. Which way is it going
> > to flow, etc. Bad news. Forth: Poly is really
> > really really expensive. Fifth: Poly is stronger
> > but scratches easier and is harder to get the
> > scratches out (I think I've got this one right)
> > Sixth: They may have different UV light properties
> > that exclude using one or the other depending on
> > your mission statemtent. Seventh: Failure with
> > acrylic is often catastrophic, meaning it's
> sudden.
> > I!
> > would imagine incipient creep with poly would
> give
> > some indication of failure, especially with strain
> > gauges attached. Some pros, some cons. Hope this
> > helps. Rick L Vancouver
> >
> >
>
________________________________________________________________________
> > Check Out the new free AIM(R) Mail -- 2 GB of
> > storage and industry-leading spam and email virus
> > protection.
> >
>
>
>
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