[Member-Forum] Moment of Inertia

Thu Mar 27 06:05:14 EDT 2014

Hi Douglas

The traditional method was to cast using a slush of polymerised powder and
liquid resin to keep the exotherm heat under control. The moulds were often
quite rudimentary and the shrinkage large so massive over thickness is
required to get what you want out of the casting. The thicker it is the more
difficult it is to keep to a cooling rate that will not cause cracks. Once
it has cracked, it is scrap. This is quite a contrast to how the material
behaves at normal diving temperatures where it is extremely forgiving and in
some configurations will extrude in preference to cracking. During the
Alicia development we did a series of destructive model tests and the
acrylic is definitely the toughest part of the submarine. We had an
instrumentation cable port in the top of the test chamber that lead the
wires out from the strain gauges on the inside surface of the test sphere.
When they went bang at around 2,500 metres bits of acrylic came out of this
¾ hole and went clean through the roof of the building. We had to make a
plastic plug to keep the debris inside the chamber. 

The German company making spheres for Triton are holding their cards close
to their chest right now. I am hoping to be able to write about it when they
they feel the time is right but for now the details remain under wraps. What
I can tell you is they start with cell cast blocks over 200mm thick that
have been slow polymerised under closely controlled conditions from 100%
liquid. This increases the length of the polymer chains with superior
mechanical properties as a result. These blocks are then heated and slowly
squeezed between two metal formers to create the basic hemispheres. After
machining and polishing the two hemispheres are bonded together using
another new technique that produces a bond that is almost invisible and
defect free.  

The new spheres are quite definitely the best that have ever been made. 

Paul

Paul Moorhouse

Design Engineer

 <mailto:paul at steel-fish.com> paul at steel-fish.com

 <http://www.steel-fish.com/> www.steel-fish.com

#44 7837 542878

From: Member-Forum [mailto:member-forum-bounces at psubs.org] On Behalf Of
Douglas Suhr
Sent: 26 March 2014 23:48
To: Dan Still; PSUBS Member Discussion Group
Subject: Re: [Member-Forum] Moment of Inertia

"Hi Paul,

can you tell us a bit more about the thermo forming of the 165mm sphere" 

I too am interested in hearing more about how such a thick personnel sphere
is manufactured. Sounds like a daunting and frustrating task (with the
multiple failures mentioned). ~ Douglas S. 

On Wed, Mar 26, 2014 at 9:17 AM, Dan Still <stillphototheater at yahoo.com>
wrote:

Anything with chips in them hate humans.

On Wednesday, March 26, 2014 7:29 AM, Joe Perkel <josephperkel at yahoo.com>
wrote:

Wow, 24+ hours for email delivery and doubled to boot. 

Can iPads go insane?

Joe <http://overview.mail.yahoo.com/?.src=iOS> 

Sent from Yahoo Mail for iPad

  _____  

From: Joe Perkel <josephperkel at yahoo.com>; 
To: member-forum at psubs.org <member-forum at psubs.org>; 
Subject: Re: [Member-Forum] Moment of Inertia 
Sent: Tue, Mar 25, 2014 4:00:01 PM 

Hi Paul,

The question is anecdotal based on an off the cuff thought of upsizing the
shell O.D. to 42" from 36". I am very hesitant to do this do to weight and
handling issues however, several members have made a compelling rationale
r/t simple comfort. At 53 I'm 6' 190 lbs and should expect that L to W ratio
to change by build time! 

I have to think a bit about the shell thickness r/t welding and corrosion
issues, but Depth no more than 350'. I seem to remember a cross section
drawing of a T section somewhere with a simple L/W/H relationship to shell
T, but can't find it again. 

I'll take that pdf if you don't mind. I'm not at home and won't be until
later this week to do some number crunching.

Thanks Paul!

Joe

Sent from Yahoo Mail for iPad <http://overview.mail.yahoo.com/?.src=iOS> 

Sent from Yahoo Mail for iPad

  _____  

From: Paul Moorhouse <paul at steel-fish.com>; 
To: 'PSUBS Member Discussion Group' <member-forum at psubs.org>; 
Subject: Re: [Member-Forum] Moment of Inertia 
Sent: Tue, Mar 25, 2014 9:10:06 AM 

Joe

As it happens, this is my day job. I have been designing submarine pressure
vessels for the last 28 years. I am sure there are others on the forum who
do this but I am happy to help if you would like, and others at PSUBS should
the need arise. 

Frame size and spacing is inter-related and there is no one answer. I have
developed some models based on the European pressure vessel code PD5500 so
running a new configuration is easy and surprisingly quick. PD5500 produces
much lighter vessels than ASME VIII which is really aimed at chemical plant.
In this way it is more similar to military codes but it does rely on quality
assurance levels that do not generally come with home construction. So to
cater for this, you put a factor in. I apologise in advance for all of the
calculations being in metric but give me info in either. 

I would need to know

·        Outside diameter

·        Shell thickness

·        Shell material 

·        Frame material

·        Diving depth

·        Length of parallel body

·        Ends, hemi or 2:1 dished.

·        Preferred frame spacing 

·        Inside or outside frames

I can send you the PDF of the work sheet as the PD5500 sums do look very
pretty. 

The next step is to design the hatch penetration and I can help you here
also. 

This guy can thermo form your acrylic

http://www.airesearch.nl/

Regards

Paul

Paul Moorhouse

www.steel-fish.com <http://www.steel-fish.com/> 

From: Member-Forum [mailto:member-forum-bounces at psubs.org] On Behalf Of Joe
Perkel
Sent: 25 March 2014 03:55
To: PSUBS Member Discussion Group
Subject: [Member-Forum] Moment of Inertia

Where did I see the rule of thumb for T-section rib sizing relative to shell
thickness? I can't seem to find it now.

Joe <http://overview.mail.yahoo.com/?.src=iOS> 

Sent from Yahoo Mail for iPad

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