In regard to the cracking at the base,
what we did on Solo’s dome was machine away the bottom several inches of
material. The part where the near 90 degree bend
occurs, and a bit above that for good measure, we got rid of on the assumption
it would be stressed.
-----Original Message-----
From: Emile
[mailto:2stroke@hetnet.nl]
Sent: Tuesday, February 22, 2005 3:00 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST]
acrylic viewport thickness
Carsten , I and an acrylic company
are also working on hot blowed domes. We got another material-left on-the-apex
than you Phil; 1/3 thickness left for an 180 deg dome. There is one dome made
with the following specs:
-angle
146 deg. (225 mm height)
We not want to go further than 170
deg. for production reasons, we encounter problems with cracking of the mat. at
the holes and at the base.
Phil, what temperature do you use
for blowing domes?
----- Original Message -----
Sent: Tuesday, February 22, 2005 7:01 PM
Subject: RE:
[PSUBS-MAILIST] acrylic viewport thickness
Hi Rick,
Yes, the whole idea of
the 120 degree design was to minimize thinning. The operating depth of the boat
is 1,750’ with ABS safety factors. It hasn’t been tested, because
it hasn’t been finished, but I’m planning to just lower it
unmanned, hopefully on a trip to Roatan which has a very deep drop-off close to
shore. I’m caught doing a refit of my other sub first, but should be back
on Solo in a few months. The cost of the dome was $1,400. Please note my dome
is way smaller than what you are looking for. Mine is only 28” in
diameter. Sorry for the telegram style writing, I’ve got to run!
Great add Phil, thanks!
Alec
-----Original Message-----
From: Rick and Marcia
[mailto:empiricus@telus.net]
Sent: Monday, February 21, 2005 5:27 PM
To:
personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST]
acrylic viewport thickness
Alec - thanks for the quick
reply.
I take it, then, that the 120
degrees results in substantially less thinning at the apex?
What's the operating depth of your
boat? How did you test it? Cost?
Those thicknesses you gave me are a
great starting point. Thanks.
----- Original Message -----
Sent: Monday, February 21, 2005 1:01 PM
Subject: RE:
[PSUBS-MAILIST] acrylic viewport thickness
Rick,
I’d
really recommend you get yourself a copy of the PVHO. It’s a little
pricey, but one of the most valuable texts out there in terms of the usefulness
of the information. What you’ll find is formulas and guidelines of a very
practical nature for calculating just this sort of problem.
There
are two basic fabrication techniques for domes; you can cast them in a mold, or
blow them with compressed air. Casting is the method on all the certified subs
you mentioned, but a cast dome costs tens or even hundreds of thousands of
dollars. For PSUBS, you’re probably looking at blown domes. A sheet of
acrylic is fastened by a ring to a flat surface. The assembly is heated, and
compressed air injected to form the dome. There’s more to it than that,
but that’s the basic approach.
One of
the challenges of blown domes is that the material has to stretch out, and can
get quite thin at the apex. It’s the minimum thickness that counts when
it comes to the stress formulae. So a trick you might want to use is to blow a
dome of fewer than 180 degrees. In my case, I went with 120 degrees. It still
looks and feels almost like 180, but there’s a very considerable
advantage in thickness and hence strength. My window is made of 2”
material, and at the apex it is 1.73” thick.
Cheers,
Alec
-----Original Message-----
From: Rick and Marcia
[mailto:empiricus@telus.net]
Sent: Monday, February 21, 2005 3:33 PM
To:
personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST]
acrylic viewport thickness
Hi, All - regarding the acrylic viewports
. . . does anyone know how thick the viewports are/were on the dome type of
subs like Hikino, Deep Flyer, PC-8, Deep Rover, etc. (Makakai was
constructed of sectional pieces glued together - beyond my skills)
I'm interested in a 6ft.
diameter hemisphere to be used to 3 atm's (30 metres) max operating
depth. One-atm cockpit.
I originally considered using the
half-dome for an ambient-dry boat but, since 3 atm's is so shallow, I may be
able to afford a one-atm viewport. I have family that I don't want to
subject to barotrauma. They're all pre-teen and still growing.
Separate issue: Anyone with a
knowledge of metal may be able to suggest framework for this half-dome.
I'm considering using 3 inch square tubing. Underkill? Overkill?
If it comes down to it, I'll just
order a one inch (at the apex) half-dome and use the boat ambiently.
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