Deep Diving Concrete Submarine
 
 
Although ROVs and small submarines like Alvin, Mir, Nautile, and others have opened a window to deep sea investigation. There has always been narrow limits imposed by the cost and difficulties of those operations. A deep sea submarine needs a pressure hull in sphere shape to resist water pressure. Since the first of those pressure spheres has been manufactured for Trieste in steel, there have been intents to fabricate them in Aluminium (Aluminaut) in Titanium, and in Glass. In any case there is no way to form thick walled spheres in any of those materials that exceed 2m of Diameter. This is why deep diving submarines are limited to passenger cabins that can host a small crew for a couple of hours not more. Therefore those boats need a mothership with crew quaters, a enourmous crane to deploy the submarine, which all means cost, cost, cost... On the other hand there exists the possibility to maintain the humans on board the ship and deploy a ROV for deep sea investigation. The weak point of ROV operation is the cable. A mile of cable needs a tremendous spooling equipment which again demands a big and expensive mothership. Spooling a mile of cable also needs a lot of time and if you operate in a sea area where bad weather is usual you can bet that a storm comes in just in the moment when all the cable is out and getting ROV and cable back in a storm is a operation of uncertain outcome that can result in loss of expensive equipment. So in best case you loose a lot of money waiting for good weater in worst case you risk and loose your ROV.
As outlined in the chapter about Deep Sea Habitat in contrary to other materials spheres made of concrete can have almost unlimited size and wall thickness. This opens the possibility for mothership free deep sea operations with short ROV cables. Which on one side could be a generally stationary concept like a 1atm Deep Sea Habitat - or a deep sea capable submarine where the pressure hull consists in a series of concrete spheres which are covered by a streamlined outer hull. At difference to existing concepts that divide the operation in a mothership-surface part and a small deep sea vehicle or ROV, this would allow to take the whole operation at 1atm to deep sea.
 
How deep can concrete Spheres go?
 
 
This is the million dollar question. You need a million dollars to get a really final and exact answer. You have to build it and to test it out until destruction - not 1 time but 3 times with hopefully very similar results. So what i can give you is a "educated guess" based on what has been done - and tests i have run.

Let me start with the facts : troll platform is based on concrete legs that reach down 303 meters with 24 m diameter and 1m wall thickness. Including usual security factors i assume that it could have a destruction depth of some double of this. Which places a positive buoyant cylinder similar as troll at 606 m destruction depth.

My submarine prototype - which i obviously did not test to destruction depth - has almost exactly the double diameter / wall thickness as troll - means it is double as strong and may have a destruction depth of 1212m -

If you check the photos at (www.concretesubmarine.com) you see that my sub floats - without ballast - on middle line - which means half of the displacement is hull weight. Bringing the concept to a extreme you could almost double the wall strength and still have positive buoyancy. Which brings us down to 2424m. This based on a cylinder shape. Given that my prototype is a spheric curved blimp shape it could stand - let me guess - 3000m - in case of a sphere shape even more - probably a lot more - this takes us down to 4000m - destruction depth - no security factor.

BUT - we are still talking about NORMAL CONCRETE - any concrete lab will tell you that special concrete as used in the core of certain record seeking buildings can increase the compression strength of concrete at least by a factor 4 compared to normal concrete. This brings us down to 12.000m destruction depth - without being limited in the size of the spheres AND still with positive buoyancy.

So including security factors of 1:2 or 1:3 as recommended for manned submarines we still could get a positive buoyant submarine based on concrete spheres that can reach average ocean depth - so 90% of the ocean floors worldwide.

Obviously i did a lot of testing before i built my concrete submarine prototype - the problem was that every time i finished a test model for testing to destruction depth i could not find a water depth that would have permitted to test it to destruction. So all i could find out is that the test models can go VERY deep and deeper than the water depth i have available.

I also put small test models inside of hydraulic cylinders where you have a liquid pressure equivalent to some 2000m dive depth. So i can say that above calculation seems to work according to my test series.

But no one can be 100% sure until building spheres in a 1:1 model and bring them to destruction depth in deep sea at a depth of thousands of meters - which is a million dollar operation i would like to get financing for...