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No. 388:
Moving Icebergs

Today, a story about four hairlike jets and an iceberg. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

If I say the word iceberg, the image of the Titanic probably enters your mind. That ghostly mountain of ice, looming out of the fog to gash your hull, is part of our collective unconscious. It almost seems we were there -- that we shared the terror of that unhappy night in 1912.

Now recall a terror that hasn't visited you yet, but one that will someday -- sooner or later. You man an offshore oil rig somewhere in the Northern seas. Out of the gloom drifts an iceberg. This time you are stationary. The ice moves toward you -- very slowly -- maybe one mile an hour. And you have no way to elude it. At first it's more beautiful than terrifying. Then you measure its size. It can weigh 20 million tons -- fifty times more than any ship on the sea. It moves like vapor, but it could crush you like an egg. And it's just as dangerous in bright sunlight as it is in night fog. What can you do?

Somehow, it has to be towed off its path. But how do you grasp an iceberg? Tie a rope around it? Throw a net over it? The trouble is, icebergs aren't stable. They roll over. Figuring out how to grasp a mountain of ice, so a ship can tow it away, is a lot harder than it sounds.

Engineers in the state of Washington have invented a way to anchor a towrope in an iceberg. The tow ship drops an odd little submarine into the water. It sidles up to the frozen mountain, just a few feet below the surface. Holding itself in place with water jets, it drills into the ice. But drilling a clean hole in ice isn't easy. They do it with four tiny jets of water, just over a hundredth of an inch in diameter. They issue from tiny sapphire nozzles at 1300 miles an hour -- twice the speed of sound.

The jets work together to hollow out a long, four-inch hole in the ice. Into the hole goes a steel anchor for the tow cable. Liquid carbon dioxide cements the anchor in place by freezing water around it. It makes a powerful adhesive. The first trials have been successful. It seems likely that tow ships will be able to exert a 50-ton pull on an iceberg. That's enough to move a really big one off course at 1/7th of a mile per hour.

What a strange study in contrasts all this is. Sapphire and ice! We create a delicate ocean ballet -- danced by elephants moving with the speed of snails. The key to grasping a block of ice, 20 times bigger than the Great Pyramid, is a set of four jets, not much bigger than the hairs of your head. As the magnitude of our technology grows it creates strange problems. And it answers them with even stranger solutions.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Kolle, J.J., Moving an Ice Mountain. Mechanical Engineering, Vol. 112, No. 2, pp.48-53.