IT MIGHT sound like the nautical equivalent of a lead balloon, but British inventor Heinz Lipschutz really did dream of going to sea in a concrete submarine. And though such a vessel has yet to surface for real, Lipschutz—who died last year aged 82—argued to the end that building his dream craft was not only possible, it actually offers all kinds of advantages over existing designs.
Lipschutz calculated that his concrete sub could dive five times as deep as metal submarines and have ten times their range and endurance. He even claimed the German Navy built a 7-metre prototype to test his theory—though this claim has never been substantiated.
Many saw Lipschutz simply as an eccentric. Yet developments in new types of high-tech concrete mean his idea may not be as ridiculous as it sounds. Building deep-diving vessels out of concrete could actually be quite sensible, says David Creswell, a submarine expert with the British technology consultancy QinetiQ, until recently an agency of the Ministry of Defence. “I quite like the idea from a survivability point of view,” he says.
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And although concrete is something we usually associate with bridges and roads, the stuff has been used successfully for a century to construct ships and yachts of all sizes. Today, American engineering students regularly build and race concrete canoes. And Troll A, the world’s biggest offshore oil platform is a 369-metre-tall structure that sits on the seabed and uses huge concrete cylinders to store oil deep beneath the surface. There can be little doubt that this material can survive extreme conditions beneath the sea. Had Lipschutz lived a few more years he may well have seen his dream come true.
The idea of a concrete submarine occurred to Lipschutz while he was still a teenager, when he and his family were living in Germany in the 1930s. He was splashing about in the bathtub one day and decided to test a new model aircraft design by “flying” it in his bath water. This experiment made him wonder: what if submarines were built more like airplanes?
A conventional submarine is built to be buoyant, kept afloat on the surface by air in its ballast tanks. To dive, it releases the air, allowing seawater to flood in. Once submerged, it can adjust its buoyancy to match the surrounding water by releasing compressed air into the tanks to displace some of the water.
Aircraft, on the other hand, are far heavier than the air they fly through, and rely on wings to supply the lift that keeps them off the ground. Apply the same principles to a submarine by sticking on a large pair of wings, Lipschutz thought, and they could generate enough lift to fly through the water. That way, you wouldn’t need to use pumps and buoyancy control systems, or worry about the craft’s density.
And that, he realised, has important consequences. If you’re not concerned about the weight or size of a sub, it could be made of much thicker, stiffer material than conventional craft are built from. With a thick, strong hull, a sub could withstand far greater pressure and dive deeper than ever before. And if you throw out any limits on size and weight, you could pack it full of freight or fuel, turning it into a long-range, heavyweight cargo shifter. The vessel could cut journey times and transportation costs by taking short cuts deep beneath the Arctic ice.
Rock solid
But what should it be built from? Most deep-diving submersibles are constructed from steel or titanium. But huge vessels built entirely of metal are expensive. To Lipschutz, the best choice seemed to be concrete. It’s far cheaper than metal, and it can take roughly twice the compressive force without crumpling—a crucial factor for deep-diving vessels. And producing ships this way would also be cheap and easy: just make a mould and pour. No need for craftsmen to spend weeks welding together steel plates. Just as heavier-than-air flying machines replaced airships early last century, Lipschutz believed these heavier-than-water concrete craft could one day replace conventional submarines.
By the late 1950s, Lipschutz had finished his design and submitted a patent application. He called his new subs underwater-planes, or U-planes, and hoping the concept would be picked up by the British Royal Navy, he made the potential military uses clear in the patent.
He claimed a fleet of 20 U-planes lurking more than 6000 metres down on the ocean floor and equipped with torpedoes would make short work of an aircraft carrier and its protective screen of destroyers. At that depth a concrete sub would stand little chance of detection and could be positioned at strategic points to defend against attacks. Their concrete exterior would reduce their sonar signature, he reckoned, and they could be quickly repositioned if detected. Yet the Navy showed little interest.
Disheartened, he turned his attention to other things. During a spell in Israel, he helped set up the nation’s first radio service. Then he trained as a navigator and pilot, and moved to Britain where he worked on a variety of inventions, including a new form of two-stroke engine, a resonance-free loudspeaker and an aircraft navigation system based on radio beacons. However none of them proved successful.
Then in 1983 he saw pictures that he believed suggested the Russians had taken the idea beyond the drawing board. Spurred on, he filed for a clutch of new patents in 1984 to cover several variations on the original design. Still the Navy seemed uninterested.
Finally, in the early 1990s, researchers at Southampton University decided to conduct a feasibility study of his design. It seemed like good news … but their conclusions were not what he wanted to hear.
Safety was their primary concern. As the vessel would be the deepest-diving submarine around, you’d be in serious trouble if something went wrong, says Philip Wilson, the engineer who supervised the study. “What if the oxygen producing system or the engines failed,” he says. Without engines, the craft would be doomed. Unlike a conventional buoyant submarine it couldn’t just float to the surface in an emergency, and no conventional submarine could dive deep enough to mount a rescue
Lipschutz wasn’t put off. He insisted that the safety issues with his submarine were no different from those with aircraft. After all, they can’t be rescued in mid-flight either. “Multi-engine design, as in aviation, will take care of the danger of engine failure, and safety design principles can be used as in aviation to attain similar safety factors,” he argued.
Wilson remains unconvinced that the practical difficulties can be overcome. On top of the safety issues, he points to difficult engineering questions. For example, if the hatches are to be made of steel, how will they be fixed into the concrete so that the attachment points aren’t weakened? “You wouldn’t get me in one,” says Wilson.
It was Lipschutz’s decision to use standard concrete that appears to be the craft’s Achilles’ heel. “Heinz wanted to use bog-standard concrete, which is good at withstanding large compression forces,” says Wilson. “Unfortunately, it has severe problems in tension—an important factor in submarine construction.”
Every time it dives and resurfaces, a submarine goes through a cycle of compression and decompression. As a submarine heads for the surface, for instance, the water pressure around it decreases rapidly—dropping by the equivalent of 1 atmosphere every 10 metres. So the submarine’s pressurised hull experiences an outward-pulling tensile force, much like that experienced by an inflated balloon as it floats high into the sky. In steel submarines this isn’t a problem, as the metal’s tensile and compressive strength are about equal. But concrete is far weaker in tension than in compression—typically just one-tenth of its compressive strength. In other words, a sub made of ordinary concrete and subjected to even a mild tensile force could crack open like an egg.
If that’s not enough to put most submariners off their breakfast, there are other problems too, warns Creswell. Space in submarines is at a premium. “From the designs I’ve seen of the concrete submarine, the thickness of the concrete is about 20 per cent of the radius of the hull.” This is twice as thick as the hull of a conventional steel sub, so you’d lose loads of valuable space for living quarters and carrying cargo, he says.
And that, you might think, would be that. However, concrete technology hasn’t been standing still. While the stuff that builders mix up with a shovel and bucket appears ill-suited for submarines, a new generation of super-strength, highly ductile cement-based cocktails have been pouring out of the labs. “It would be very interesting to try and make a concrete submarine using modern ultra-high-performance concrete,” says Mikael Hallgren, a concrete expert at construction consultancy Scandiaconsult Sverige in Stockholm.
In the early 1990s, engineers at the French construction company Bouygues developed a novel concrete mix that is up to 250 times as strong as conventional concrete. Called reactive powder concrete (RPC), it is made by mixing Portland cement, a fine silica powder called silica fume, crushed quartz and small sand crystals with a plasticiser, steel fibres and water. This stuff has been used in bridges and for buildings in earthquake zones. And if you replace the sand crystals with mineral filings, heat the resultant mix at 400 °C for 48 hours, its compressive strength can be pushed to over 800 megapascals: that’s twice the compressive strength of steel and approaching that of titanium. Its tensile strength, however, is still a mere 50 megapascals, compared with 400 megapascals for steel.
So could it be used to build a sub? “I wouldn’t be any more worried stepping into a submarine made of RPC than into an ordinary submarine made of steel,” says Hallgren. And Vic Perry, managing director of Canadian company Ductal that manufactures RPC, believes that if reinforcing ribs were built in to the hull, RPC could be a very attractive alternative for constructing subs. “As the RPC compound’s characteristics become more like steel, so the design issues are more akin to those facing steel structures,” he says.
And RPC isn’t the only contender. A team of students led by engineer John Gilbert at the University of Alabama at Huntsville has developed a concrete that achieves, proportionally, an even greater tensile strength than RPC. Using a mixture of hollow glass spheres a tenth of a millimetre in diameter, latex, acrylic polymer, graphite fibres, Portland cement and water, the team has created concrete with a tensile strength that is 37 per cent of its compressive strength.
The concrete was developed specifically to be light and flexible, to build a craft that would take part in an annual national concrete canoe race among American engineering students. During last year’s race Gilbert noticed something odd about his team’s canoe. Though its rowers were not the strongest, they won the competition, managing to beat all the other teams by a significant margin. “I don’t think this was just coincidence or luck,” he says.
Gilbert believes the concrete canoe gave them extra forward thrust by wiggling like a fish. It wasn’t intentional, he says, but the rowers seemed to force the boat to vibrate close to its natural frequency. This meant that some of their energy was being released through the canoe’s hull. The way that a fish moves its body as it swims makes it very efficient, he says. “I believe our canoe moved in a very similar way.” Gilbert and his students are now studying the material with the hope of producing some concrete evidence to support the theory.
Crucially, he says, the phenomenon could only be produced in a vessel made using his concrete mix. In most structures you want to stay away from the resonant frequency because there is the danger that the structure might shake itself apart, he says. “But because our concrete is so flexible it can withstand these bending forces and translate them into useful work,” he says.
“We’re already examining the possibility of building some airplane parts out of our concrete because it is much more resistant than steel to explosion and other extreme forces,” says Gilbert.
He has little doubt that the material would be of equal use in designing craft for missions beneath the waves. “Our concrete would be a very good material to build a submarine. You might even engineer it to take advantage of the structure’s resonant frequency to swim like a fish.”
Don’t expect to see a wiggly concrete submarine any time soon. But keep an eye out for a more conventional version. Muthian Gunasekaran, a concrete specialist who runs Sekar Enterprises, an engineering company based in California, hopes to be the first to build Lipschutz’s dream boat.
Gunasekaran won’t say too much at the moment, but he is confident that the craft is feasible. And to prove it, he’s already taking the first steps. “We are doing conceptual studies and hope to build some small scale models for testing,” he says. Lipschutz may be gone, but the hunt for his concrete Red October isn’t over.
