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Re: [PSUBS-MAILIST] Introduction

So your concern about FC is with buckling, given the fairly thin sections? That would seem to be compensated by very high bending strength. Reinforcing ribs would probably be anything but, as they would serve as stress raisers. Wish I could find actual tests, though. There's a fair amount of literature on FC cylinders HOLDING pressure - it's used for tanks and reservoirs - but I've never seen anything on its use under external pressure.
I should look again at the Soviet-era book on concrete ships that the Defense Department translated. If there's anything, it will be there. Problem is the print quality is so bad that I can't read it for long before needing a break. The terminology used by the translator is also confusing; I have to keep reminding myself that in that book "reinforced concrete" means cement mortar with mesh reinforcement - ferrocement in other words - while "ferro-concrete" (armotsement) is what we call reinforced concrete. 

Best,
Marc

Brian Cox wrote:

Hi Marc,  You're right about the free-flooding and the no pressure
differential.

 I think that if one were to make a pressure hull out of concrete you would
want to do what Ian is doing, and that is make a very thick walled vessel.
This would be in the realm of re-enforced concrete which would be 10 to 12
inches thick.  Ferro-cement would not be a very good material for resisting
pressure. Steel is better, steel has many advantages.  When you start to go
with very thick concrete the cost is going to exceed what you could do in
steel, or at least equal it.

  That being said, you may be able to build a ferro cement sub that was
constructed in such a way that it would have many re-enforcing ribs on the
inside to increase the strength, but it would reduce your inside space
considerably.  It would not be able to go very deep, maybe only 30'.  You
would need to test some hulls to destruction to really know how much they
could take.

Brian

-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of F. Marc de
Piolenc
Sent: Tuesday, November 03, 2009 4:50 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Introduction


Thanks for the link. I take it, then, that your FC component is all
free-flooding when submerged - no differential pressure? May I ask why
steel for the pressure hull; is it just because of the lack of Code
coverage?

Best,
Marc

Brian Cox wrote:

Hi Marc de Piolenc,
                      That would be me, however the part of my sub that is
ferro-cement is only a ballast / superstructure.  My pressure hull will be
steel much like many of the other members.  Here is a link to the psubs

site

and what I have done so far.

http://www.psubs.org/projects/1234567812/ferrosuperstructure/

Brian

-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of F. Marc de
Piolenc
Sent: Monday, November 02, 2009 2:31 PM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Introduction


New member here.

American/French dual national, mechanical engineer by training
(aeronautical by predilection), interested since childhood in submarines.

I've wanted to build a ferrocement sub since I first learned of the
material in my late teens (mid-fifties now). I understand there is
another list member who is actually building in ferrocement.

Best to all,

Marc de Piolenc
Iligan City, Philippines
http://www.archivale.com



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