Now It Can Be Told! - Man-Made Islands and Floating Bridges
British scientists have found a way of increasing the natural surface tension of water, making it technically possible to build a mid-Atlantic aerodrome or a floating cross-channel bridge, it was disclosed by the Admiralty in September 1945. This latest discovery in engineering-on-water began when an inventor's brain-wave sent him motor-cycling at 50 m.p.h. Along a tarpaulin stretched over a river ford. The new discovery has been sponsored and developed by the Royal Navy, and brings dramatic dreams within the realms of actuality.
Ordinary tension will support a needle on the water's surface. By putting a flexible synthetic surface on the sea, and by increasing the tension about 400,000 times, it has been found possible to support heavy lorries and aircraft in mid-ocean. One practical result of the discovery is the production of man-made “islands” – composed of hundreds of hexagonal buoyancy cans – “islands” which can be built to any shape or length required, and which can be easily dismantled, transported and reassembled. Another, which has already stood up to the severe practical tests of war, is the “Swiss roll”, a floating pier that can be rolled up, carried on board a ship and later rolled out again from ship to shore. This pier is nearly twenty times as light as a Bailey bridge of equal length, yet it will carry a nine-ton lorry.
Inventor of these new devices is Mr. R. M. Hamilton, of Victoria Street, London, who served at the beginning of war as a Petty Officer in the Royal Naval Patrol Service. He is an inventor by profession. Co-operating on the involved mathematical calculations required was Mr. J. S. Herbert, Housemaster at Eton College. “Further developments form the original discovery are being made”, Mr. Hamilton said, “but for a time their nature must remain secret”.
It was in 1944 that the first practical result was employed – the “Swiss Roll” pier, used in the Normandy invasion. In this flexible canvas-and-wood jetty, a tension of 18 to 30 tons is applied to any length stretching from ship to beach and the result is that a laden lorry can be driven ashore in safety over the sea. Some 2,700 feet of “Swiss Roll” were in continual use at the invasion harbour at Arromanches in spite of the appalling weather that, unluckily, was encountered there.
The Navy's latest experiments, only recently concluded, have been with a further development of the same fundamental principle, the “Lily” floating airstrip. Given its name because of its resemblance to a carpet of lily leaves on a pond, “Lily” is a very different proposition to “Swiss Roll”. It consists of numbers of buoyancy cans with hexagonal surfaces, so linked together that they “give” in a controlled manner to the motion of the sea from any direction, yet remain sufficiently rigid to take the weight of a heavy aircraft. Whereas in “Swiss Roll” tension is applied externally, “Lily's” hexagonal surfaces, when linked together, create their own tension.
The Navy's experimental airstrip is the smallest on which practical tests could be undertaken, 520 ft. long and 60 ft. across. On this an aircraft, laden to 9,000 pounds, has been landed and has taken off again. A strip of this size can be assembled by 40 men in one hour. At present the cans are only six feet across and 30 inches deep, but their size could be scaled-up to take greatly increasing weight.
The whole surface of “Lily” is flexible so that it will not break up, but this flexibility is controlled by the use of underwater dampers.
“With Straws in Your Hair”
The inventor claims that with the latest dampers more than three tons pressure is required to move the surface at all, and that “Lily” will remain flat in waves up to 36 ft. from crest to crest. The dream of Atlantic aerodromes has hitherto been unattainable because it has not been possible to build large enough stormproof flat-surface structures. Modern transport aircraft would need a carrier or a strip twice the length of the Queen Elizabeth, largest ship in the world. Such a floating structure has hitherto been impractical. The Navy's new “seadrome” can be transported in ships and assembled anywhere. With the present size buoyancy can, a “Lily” 2,500 feet long, could be transported in three merchant ships.
“Lily's” possibilities for bridge-building are underlined by those responsible for its development. “To mention a cross-Channel bridge immediately places you with straws in your hair”, said Mr. Herbert, the mathematician, “but we can say that it would be possible to build a floating bridge 22 miles long that would not break up in a sea.”
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