Concrete Submarine

I was reading about the submarine HMS Astute the other day, and somewhere I came across a line that said that in order to be able to withstand the pressure during deep dives, the cross section of the hull needs to be a perfect circle. Well, perfect is something you only get in theory, in practice you can come close, but you are never going to be perfect. So, just how perfect does it need to be? Pretty darn close: a flat spot that deviates from a perfect circle by one inch will cause a 30% loss in strength. We are talking about a seven inch thick steel plate bent in a circle 37 feet in diameter.  That's going to be a bit of a trick. No wonder submarines are so expensive.

Pont du Gard Roman aqueduct near Nimes in France

Then I got to thinking about this and I realized steel was exactly the wrong material for this. We use steel to build things because it has high tensile strength. When you are building a tank to hold compressed air, steel is a good choice. But a submarine is not dealing with internal pressure, it is dealing with external pressure, and for that you need a material has strong compression strength, like rock, or concrete. Look at the Roman arches or tunnels, or sewer pipes. All require good compression strength and all use stone or concrete.

Concrete Submarine

Then I remembered reading a few years ago about a possible new submarine threat in the form of concrete submarines, so I went a-Googling. I found a couple of references to this, but nothing current. I also found one site that specializes in private/commercial submarines. Near as I can make out, one German engineer built himself a working concrete submarine, and then tried to promote the idea. A few years ago he moved to Columbia where he has been working on a larger luxury yacht style version.

Why does the Navy persist in building submarines out of the wrong material? Possibly because they resist explosives, as in depth charges, better. Or maybe just no one has ever built a big submarine out of concrete and no one wants to try it. You know the first reaction some people have when they hear the words "concrete" and "submarine" together is that's a really great idea, it will go straight to the bottom and stay there, and then they laugh. But steel by itself doesn't float any better. Maybe it's just that that's what the Mafia uses. I mean, who ever heard of steel overshoes?

Update October 2016 replaced missing picture, fixed by HTML, which meant replacing more pictures.