Alan,
The inside curve at the base of the dome is a high stress area that cannot
be completely relieved with annealing. Early Stachiw experiments tried
different methods of reinforcing this area with poor results. It is best
to
machine the flange off. This is why Kittredge did not use the formed
flange
as a hold down but glued a ring on the outside instead. As far as
reinforcing material goes, the only thing you should use is acrylic and
acrylic monomer. Even though other materials may have good adhesion (and
some even better than acrylic) there are many other factors to consider
such
as different coefficients of thermal expansion and cyclic fatigue. At the
present, Lloyds no longer certifies glued rings as a hold down. Most domes
on certified subs built today use straps or "crash bars" to hold them
down.
Greg
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Alan James
Sent: Friday, August 07, 2009 4:27 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Tympanic membranes
Greg, you're just the person I need.
I have a blown dome 500mm OD & 25mm thick being made for me at the moment.
The guys read the Stachiw book.
I also own another at 10mm thick. I'm intending to cut the flanges off to
within 10mm
& mount the base inside a block of vinyl ester/fiberglass.
( build up the vinyl ester in a mold slowly around the dome base)The 10mm
flange being
to key it into the block. This block will support the weak inside curve at
the base of the dome.
I will then anneal them, clamp them to a plate & test them at depth.
The 10mm dome will be pushed near its design limit as its kind of surplus.
Vynil ester is used in the bathroom industry backing acrylic & I think has
a
80/85%
adhesion strength. I will mount my hatch hinges & closing mechanisms on to
the block.
I'm intending to use it to 250ft depending on the apex thickness.
Any thoughts/ reservations on this idea.???
Frank, heres another link to of the shelf electrical connectors I found
while googling
for Gregs suggested supplyer. It has a lot of clear diagrams if you open
the
PDFs
http://www.seaconbrantner.com/Products/glass_reinforced_epoxy.htm
Regards Alan
----- Original Message -----
From: "Greg Cottrell" <greg@precisionplastics.com>
To: <personal_submersibles@psubs.org>
Sent: Saturday, August 08, 2009 2:43 AM
Subject: RE: [PSUBS-MAILIST] Tympanic membranes
The reason I keep harping on the benefits of the PVHO is due to a trend
I've
noticed over the last few years. I'm an acrylic fabricator that started
making domes and viewports back in the 1980s. At that time, all the folks
that I made them for were either using a set of Kittredge plans or a copy
of
the PVHO. I don't know how many domes I've made over the years but it's
been
quite a few. I was fairly confident that most of these guys would be just
fine as far as safety was concerned.
But then over time the requests started to be for domes that "look like a
jet fighter canopies" or viewports made from polycarbonate, or with
drilled
holes, formed flanges, etc. Some told me that they knew more about
acrylics
(and general pressure vessel design) than the ABS. I gave a talk on
viewports at the 2006 PSUBS convention that at one point, turned into a
debate. Now I had to worry about liability. After that, I would try to
pick
and choose who to help based on whether I thought they were going to get
killed in their "innovative designs". About a year ago I decided to stop
fabricating viewports all together.
I wish everyone had their own sub! But if there comes a day when a
submarine
death hit's the news, regulation in going to clamp down on us like
nobody's
business! You think you don't like ABS now?! If that happens, the party
will
be over.
Greg
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: Friday, August 07, 2009 9:44 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Tympanic membranes
I was headed down that path as well. The best defense is a good offense,
or follow ABS/PVHO rules and build it right and you won't have much to
worry about. If you design, build, and rate the sub correctly, and only
dive in water no deeper than the sub rating you should never have a
reason to bail from the sub. The Seaker100 accident (read the web site)
is factual evidence that the likelihood of surviving a catastrophic
failure is slim to none. That vessel failed in 30 feet of water
resulting in one dead and one critical who survived, but by his own
admission had no time to "react" and has no idea how he reached the
surface.
However, building true to ABS/PVHO specs won't guarantee you don't get
yourself into an entanglement situation. This seems to be a valid reason
to discuss escaping a sub and having some kind of plan for it. The video
clip of Alec hitting that underwater cable with snoopy is a perfect
example that there are underwater obstacles out there that can ruin your
day, even though it didn't ruin his. Had that cable gotten caught within
the claw arm on the front of Snoopy it would have been a far different
situation. I don't recall if that was a private dive or one that he made
at the 2006 convention, but we should look at that situation sometime in
the future and imagine the cable ensnared the sub, then discuss, "Ok now
what?"
Last year we started some discussions about equipment, parts, or
placement thereof that we might build on our subs as "standards" so in
case an entanglement situation arose an outside support team and/or
rescuers could understand how to get us additional air, locate lift
hooks, etc. We've let that discussion falter and should get back to it
since it represents an opportunity to deal with a situation without
forcing the occupant to escape. And lastly, directed to everyone, Jay
Jeffries has a lot of practical knowledge on issues surrounding sub
escape and has spent two consecutive conventions discussing the topic.
He should be listened to.
Jon
Greg Cottrell wrote:
I also agree with Dan. No offense, but I think that it is very
interesting that some folks would say that following the PVHO is "over
kill" on safety and not necessary but then spend all their energy
planning to escape from their sunken sub. An escape plan is a fine
idea, but it would be nice to see more of that energy spent on safe
building practices that are proven than "internet innovation with a
great escape plan"
Greg C
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