Concrete submarine

Wilfried

You may have considered this, but people do need to be aware that the applications you list in your website are not subject to the high stress cycles that a diving vehicle experiences.
The loads from pressure in your examples are essentially static when you consider the stress range your diving vehicle will be subject to.

Fatigue response is always the worry and the limiting factor. Micro-crack propogation is going to be your main concern with any brittle material. This has been researched and well described in engineering circles over the years. A lot of effort in the past has been put into research minimising fatigue cracking in concrete, with fibres added to the matrix, even steel fibres, but inevitably it's easier and cheaper to use another material.


The proposed cementitious pressure hulls considered by Russian engineers were extensively material tested. They found they needed to use a fine ceramic powder and cement morter with a kevlar lining for this application.
Reducing the particle size reduces the crack generation at morter aggragate interfaces which accelerates fatigue failure.

Steel is a very good matierial if you really want to deep dive rather than close surface dives.

For example the well known U-boats had a 18.5mm thick pressure hull 4.5m in diameter with transverse ring frames 700mm apart and 11 by 200 mm bulbed profile. The mild steel they used was not as good as todays mild steels and they had a working depth of 300ft. Crush depth was much deeper.

The point: Its easy to make a pressure hull from a commercially available large steel pipe section, and it can be efficiently streamlined with nicely moulded composite bolt-on fairings.
However the question I am leading up to that should be asked is "why haven't more people done this ?"

The answer is something that seems to be eluding this discussion.
The pressure hull is the simple bit; It's the systems that let it operate safely and effectively that are the catch, and just how you integrate these systems into the hull and what the compromises are.

 

Im all for new and crazy ideas
but Ild still be carrying flowers, dressed in my best and chiseling my name and epitaph in that thing before I got on board

Ive built a lot of stuff in my days as a contractor
and concrete has got more than its share of variables
I lived on the water for eons as a kid
Ive a healthy respect for the power of the ocean
it wants you its got you
and concrete woudnt be my first choice of survival suit's
hell I dont even like steel or fiberglass sail boats
in a pinch
I want something that floats underneath me

best of luck though
Im not trying to pop your balloon
just a little healthy skepticism
best
B

 

I would say there are by far more severe examples of cycle load on concrete out there than a submarine hull - a bridge, a highrise building in wind load, Troll A is also not as static as one would think - it bends quite a lot under wave impact - it was calculated for 180 million load cycles - should be enough for sub too...

...its the systems - yes for a military sub - not necessarily for a civilian sub - buoyancy control is not rocket science ...

... "why haven't more people done this ?" - there are lot of examples - most in other engineering fields - it needs to take a look outside the box -


Concrete suitable material for pressure hulls
Title : Long-Term, Deep Ocean Test of Concrete Spherical Structures - Results after 13 Years.

Descriptive Note : Technical rept. Mar 78-Nov 84,

Corporate Author : NAVAL CIVIL ENGINEERING LAB PORT HUENEME CA

Personal Author(s) : Rail,R. D. ; Wendt,R. L.

Report Date : JUL 1985

Pagination or Media Count : 70

Abstract : In 1971, a long-term, deep-ocean test was started on 18 pressure-resistant, hollow concrete spheres, 66 inches in outside diameter by 4.12 inches in wall thickness. The spheres were placed in the ocean near the seafloor at depths from 1,840 to 5,075 feet. Over a 13 year period, annual inspections of the spheres using submersibles have provided data on time-dependent failure and permeability. After 5.3 years of exposure, three spheres were retrieved from the ocean for laboratory testing, and after 10.5 years two more spheres were retrieved and tested. This report is the third report in a series describing and summarizing the findings from the ocean and laboratory tests. Data on concrete compressive strength gain, short-term implosion strength of the retrieved spheres, and permeability and durability of the concrete were obtained. The data have shown that concrete exhibits good behavior for ocean applications. High quality, well-cured concrete can be expected to gain and maintain strength when submerged in seawater under high pressure. Concrete is a durable material in the deep ocean; neither deterioration of the concrete matrix nor corrosion of reinforcing steel are problems, even though the concrete becomes saturated with seawater. Uncoated concrete has a very low rate of premeation of seawater through the concrete and even this small flow can be prevented by a waterproofing coating. (Author)

Descriptors : *CONCRETE, *STRENGTH(MECHANICS), *UNDERWATER STRUCTURES, *DEEP OCEANS, THICKNESS, PERMEABILITY, LABORATORY TESTS, CORROSION, TIME DEPENDENCE, FAILURE, HIGH PRESSURE, SPHERES, DEPTH, STEEL, SHORT RANGE(TIME), COATINGS, STRENGTH(GENERAL), GAIN, INSPECTION, WALLS, FLOW, OCEANS, DETERIORATION, SEA WATER, LOW RATE, OCEAN BOTTOM, REINFORCING MATERIALS, COMPRESSIVE PROPERTIES, WATERPROOFING, SUBMERSIBLES, IMPLOSIONS.

Subject Categories : PHYSICAL AND DYNAMIC OCEANOGRAPHY CERAMICS, REFRACTORIES AND GLASS

Distribution Statement : APPROVED FOR PUBLIC RELEASE

source: http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA160232

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...seems that some have done it...


Cheers,
Wil

 

Hello Boston, if diving and submarines, bring up several nightmares in your mind - a submarine yacht is probably not your thing...sinking to the ocean bottom in a steel coffin would not make that better right? - thanks for your best wishes...

Cheers,
Wil

 

Wilfried
Before you can draw comparisons or quote numbers you need to state exactly what you are comparing.

compressive Pressure cyclic loading is your bugbear, the supporting structures (bridge bases caissons tunnels etc) you are talking about here are not cycled through the compressive stress. The 180 million load cycles is the structural response to wave and wind loads not the predicted fatigue strength to repeated immersion to high pressure, there is a big difference here.
Consider what I said:

The spheres left on the ocean floor are a classic case , sure they are durable but on the S-N curve we are looking at 1 stress cycle (one dive).
If you want to repeatedly dive deep you will need to do some very comprehensive material testing specifically to determine the safe number of cycles. You cannot rely on these sorts of observations.

For shallow dives and even deep static underwater habitat, it would be safe to base your engineering on these types of examples, but I am worried about the fatigue limitations of this material in this application for repeated significant loading. I am also worried that you may not be aware of this.

 

well having read this thread and another were this was discussed in its entirety
Ill have to give Welmer his due for putting up with a lot of skepticism
and the occasional blunt comment
along with a little bad humor on my part

as far as going underwater is concerned
Ild love to own a personal submersible kinda like old Calypso's diving saucer
I loved that thing
my issue with the hole idea is Ive worked in concrete
and Ive worked with a lot of red iron as well
steel I can trust
as long as I am not trying to float
Im ok with it
concrete
I just dont trust the stuff
one good crack on the bottom and splash
your swimming
thing about steel is you can hit something and have a reasonable chance of survival
in a thin concrete hull
Ild be really nervous about that

 

If I were just looking for an underwater fun boat, my choice would probably be a fiberglass wet sub. Safety assured by your wetsuit, small, nippy, relatively cheap and if it heads for the bottom easy to escape and swim to the surface. I saw several of these things in the Mediterranean, they've been around for years and are probably available commercially.

 

ya some guys made em out of wave runners I think to resemble dolphins
but they dont stay submerged for long enough
oh well
some day
when Im rich and famous

oh and you are right about the option of jumping ship
could come in dam handy in a pinch

 

The wet subs I was were at Comex Nucleaire in Marseilles, which was at that time an offshoot of an underwater services company. They had dozens of old purpose-built subs of various descriptions, both dry and wet, some obviously for seriously deep work, scattered around their grounds.

A couple were really neat, with clear plastic screens around an open two place cockpit like a small helicopter, no vanes that I saw but several small rotating steering pods and 2 drive props which appeared to be fixed. Can't remember where I put the photos.

It occurred to me at the time (about 15-20 years ago) that they would sell well to keen divers. I haven't seen any for sale though, which is surprising. Probably due to damn lawyers.

 

cycle loads

Hello Mike - i give you that TROLL A is not exactly the same load case - it is a much more severe load case including bending cycles and vibration.

I am not a concrete material scientist - but what i do know is that a bridge fundation is taking a pressure load cycle every few seconds - so it will take the number of load cycles that you have to expect in a sub hull - in less than a few hours - does the concrete come to the end of his fatigue life in a bridge within a few days? - not really - so i would not expect fatigue in a sub hull before some centuries of use - i honestly think your idea of failure by fatigue by dive cycles is out of proportion some serious orders of magnitude...

I also think that the reason for the studies design with the concrete spheres that obviously skips completely your postulated "cycle problem" is just due to the fact that there is no "cycle problem" and therefore no need to include it in a "is concrete a suitable building material for submarine applications" study.

On the other hand i am well aware of load cycles and fatigue especially the 10.000 cycle limit for acrylic viewports. The comet accidents with aluminium pressure hulls in airplanes - etc.

In general i am a friend of treating a sub hull like a scuba tank - check it every couple of months with a testdive that gives you at least a safety factor of 1:3 - expect the unexpected test it frequently

Cheers,
Will

 

I moved my question of mine over over so we have just one thread..:

"I am very interested in this cruising concept but would like to know at what depth the 18m sub will operate when the snorkel is deployed. Further when cruising deeper, how long can a dive be sustained and what is the duration of the propulsion engine while submerged?"

And I have a further question Wil:

When you say at a depth of 4,6m, is this the depth to the top of the hull? At what sea state will you be able to operate in when cruising at this depth of 4,6m? And what is the snorkel length for this operating depth?

Thank you

 

snorkel depth

Yes the mentioned studies (http://imulead.com/tolimared/concretesubmarine/anuncios/ay) suggest that 4,6m at the top of the hull is kind of minimum to get the most efficiency out of "submerged cruising" - so i would go for 4,6m of snorkel with a streamline cover (water covered part) and then for some 5 m more (simple tube) that sticks up in the air. This will give not only safety that snorkel top will not submerge in waves, it will also give you a "high point" to mount a "look around" camera, a flash for get seen at night, radar reflector, a dive flag, a nationality flag (important in US waters due to new legislation). I am confident that this configuration will give a smooth cruising in typical "open ocean trade wind conditions" - so it is for now my favorite. On the other hand a long hose snorkel will give you a lot more cruising depth the limit is the hand ability of the hose, the resistance of the air in the snorkel that tends to lower engine performance, the drag of the hose - it looks to me that some 20 m snorkel depth are manageable according to the tests with the prototype. Third concept i have in mind is a tandem concept where a diesel electric generator is pulled on the surface behind the sub - as electric lines are thinner you could cruise even deeper without too much drag - it also has some practical advantage as you can disconnect your surface part on the anchor place and use it as a tender. In general the hose and tandem concept bring up the "entanglement discussion" but i think this should be no problem when cruising in open ocean and you could just pass the lines over a cable cutter so you can cut them if the need comes up - as you see i am not a big fan of the "traditional military submarine configuration" with batteries chlor gas and shortcut danger

Cheers,
Wil

 

Thanks Will,

May I present another question or two?

What wave height will the 18m sub be able to cruise in when motoring at a depth of 4,6m?

Also- I see no means of controlling pitch or roll. At your proposed cruising speed of 3kt, how will the pitch be controlled while cruising?. When cruising submerged, will a forward pitch (nose down), cause a change in depth by the alteration of flow over the hull?

Thanks again

 

At what wave conditions things will become bumpy for the 18m sub - the sea trials will give the final answers. At the moment i do only count with the experiences from the prototype which was 10 times smaller. I had snorkel trips at less then 1m depth and when i came up i found that a severe storm had come up and several sailing yachts (of the ocean crossing type) where calling SOS - i did not even notice the weather conditions change! - i assume the the much bigger sub will be capable of cruising in even more severe conditions without any movements. My current eperience ist that a normal storm will present no problem - a cyclone may be a reason to go a bit deeper - have not experienced one yet - in any case if i ever should experience one - a submarine yacht would be my first choice - general speaking - given the experience with the prototype - i would not expect to have to take a filled coffee cup from the table in any ocean condition - nor to bring up a spit bag.

What concerns pitch and roll control - the deep ballast center keeps the boat on even keel, i have not experienced ANY pitch or roll under any condition in the prototype - IF perceptible movements come up it is a up and down on even keel - absolutely not sea sickening.

If you are concerned about pitch (nose up) generated from the snorkel at cruising speed - it has not been a problem either.

Cheers,
Wil

 

Thanks Wil,

Do you believe that the hull was exposed in the wave trough during this storm?

Thanks again