The world's oceans claim on average one ship a week, often in mysterious circumstances. With little evidence to go on, investigators usually point at human error or poor maintenance but an alarming series of disappearances and near-sinkings, including world-class vessels with unblemished track records, has prompted the search for a more sinister cause and renewed belief in a maritime myth: the wall of water. Waves the height of an office block. Waves twice as large as any that ships are designed to ride over.
These are not tsunamis or tidal waves, but huge breaking walls of water that come out of the blue. Suspicions these were fact not fiction were roused in 1978, by the cargo ship MÃ¼nchen. She was a state-of-the-art cargo ship. The December storms predicted when she set out to cross the Atlantic did not concern her German crew. The voyage was perfectly routine until at 3am on 12 December she sent out a garbled mayday message from the mid-Atlantic. Rescue attempts began immediately with over a hundred ships combing the ocean.
The ship was never found. She went down with all 27 hands. An exhaustive search found just a few bits of wreckage, including an unlaunched lifeboat that bore a vital clue. It had been stowed 20m above the water line yet one of its attachment pins had twisted as though hit by an extreme force. The Maritime Court concluded that bad weather had caused an unusual event. Other seafarers could not help but consider the possibility of a mythical freak wave.
Freak waves are the stuff of legend. They aren't just rare, according to traditional views of the sea, they shouldn't exist at all. Oceanographers and meteorologists have long used a mathematical system called the linear model to predict wave height. This assumes that waves vary in a regular way around the average (so-called 'significant') wave height. In a storm sea with a significant wave height of 12m, the model suggests there will hardly ever be a wave higher than 15m. One of 30m could indeed happen - but only once in ten thousand years.
Except they do happen with startling frequency. Since 1990, 20 vessels have been struck by waves off the South African coast that defy the linear model's predictions. And on New Year's Day, 1995 a wave of 26m was measured hitting the Draupner oil rig in the North Sea off Norway. Concerned shipping operators wanted to know what was going on. The largest wave marine architects are required to accommodate in the design strength calculations is 15m from trough to crest. If that assumption were to be proved false, the whole world shipping industry would face some very tough choices.
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