Re: [PSUBS-MAILIST] concrete submarine

[Michael Edwards <me@sustainkauai.org>]

Hello Wilfried:

diagroto@ibague.cetcol.net.co wrote:

> Hello Michael, curtis, brian, Gene, Carsten, everyone interested,
>
> In my opinion to do a sub you can get in and out are two proven concepts.
> A simple wet sub at ambient pressure, or a bigger dry sub with diver chamber
> like carsten did. Altough i think that anything else is possible i would be
> careful not to combine disadvantages of various different and proven concepts.
> (water in sub, pressure regulation-complicated, floating regulation, etc.)
> Anyhow i agree with carsten that this is a new idea worth to explore.
> Would not do it with a concrete hull. (sensible to internal overpressure).

Thank you Wilfried, for pointing out the "fatal flaw". You were clear in your
earlier threads
that concrete shines in compression, not with pressurization. I guess I presumed
that like water tanks, the material could stand a certain amount of
pressurization/
tension?

> You also should be aware that there is a BIG difference between ferrocement
> construction (meshing glue cement in...) and massive concrete construction.
> Ferrocement is a concept that is used in yacht building only (not other
> engineering ) had a LOT of problems especially rusting of mashing and crackling
> due to not optimal use of concrete and lack of proper compactation. It also is
> specially problematic for small yachts below 10m due to thin walls while it can
> be used with relative good results for bigger yachts.
> Massive concrete is widly used in submarine tunnels (salt water under pressure)
> in drilling platforms (wave action) and offshore oil tanks and dam building in
> same or more severe conditions than it would be in a sub.
> In all this conditions concrete is compacted as in normal construction what
> limits it to walls of 5cm minimum. - You need 2cm of concrete above steelbars
> as minimum to avoid rust and distribute forces. You need space in your mold to
> bring concrete in and compact it properly.
> I had a double mold (kind of gliding mold as used for television towers or
> bridges, boat consists in cone shape rings with variable diameters - no secret)
> This means i did a cone shape ring every week and form was made to be recycled
> and to adapt to any ring diameter and wall thickness on both ends.

I have a million questions here. How many days did this "pour" take?
Were the cones added on to an "internal" male mold? Or were cones
used for both the inner and outer forms? Was the hull formed on it's
side or standing upright? What material did you make the forms out of?
I have seen slip forms in cast buildings but nothing anywhere near this
complex of a form in concrete.

> You are completly right, if you do not compact your concret properly during
> construction (as in many ferrocement constructions) you will have a poor
> crackling water barrier, endless rusting of steelbars - final failure. If you
> do it right you will have your steel completly protected (2cm below surface).
> Every building material has its limitations. And one of the limitations of
> concrete is wall thickness below 5cm. This makes it little ideal for small
> trailerable wet sub. But it can be used with excellent results for bigger thick
> wall pressure standing dry sub.
> Greetings
> Wilfried

Wilfried; do you feel in retrospect, that the small 2 meter sub was the wrong
material
for this small size? As a practical matter, what is the minimum size you
would recommend for a "dry" concrete sub?

Thank you

Michael