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May 11, 2007

Strange But True!

Q. It was 1893 and the ship “Fram” was making an epic attempt to reach the North Pole when along the coast of Siberia a mysterious thing happened. The vessel could manage only 1.5 knots instead of its customary 7, and control of the ship was so bad the captain was forced to travel in loops to escape the area. Yet the weather and water were seemingly calm...

A. The Fram had encountered what is now called “dead water,” where a layer of fresh water from a river emptying into the ocean overlay salt water, creating an unusual double-wave set, says Jearl Walker in “The Flying Circus of Physics.” The first set of waves were the usual surface ones, but in addition waves had formed down below along the interface between the two types of water, creating drag upon drag. So the faster the vessel tried to go, the faster its energy was draining away. Plus, its length happened to be such that the rudder was right above a crest of the internal waves, wreaking havoc on maneuverability. End of mystery!


 
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