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 München. 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.
"We hoped to find at least a life-raft with people. We never found a living soul" |
Captain Pieter de Nijs, München search co-ordinator |
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.
What could cause such extreme waves? Curious about the spate of
South African incidents, oceanographer Marten Grundlingh plotted the
strikes on thermal sea surface maps. All the ships had been at the edge
of the Agulhas Current, the meeting point of two opposing flows mixing
warm Indian Ocean water with a colder Atlantic flow. Radar surveillance
by satellite confirmed that wave height at the edge of this current
could grow well beyond the linear model's predictions, especially if
the wind direction opposed the current flow.
Problem solved: the answer was just to avoid certain ocean currents
in certain weather conditions. There was nothing freakish about large
waves; the mariners' myth was an explicable phenomenon. To science,
this was one that didn't get away.
"Out of nowhere... a wave twice as high as average. The ship went down like freefall" |
Göran Persson, Caledonian Star First Officer |
Unfortunately, ocean currents could not explain two near disastrous
wave strikes in March 2001. Once more two reputable ships, designed to
cope with the very worst conditions any ocean could throw at them, were
crippled to the point of sinking. The Bremen and Caledonian Star were
carrying hundreds of tourists across the South Atlantic. At 5am on 2
March the Caledonian Star's First Officer saw a 30m wave bearing down
on them.
It smashed over the ship, flooding the bridge and destroying much of
the navigation and communication equipment. The Caledonian Star limped
back to port, her crew and passengers grateful that the engines had
kept running, despite the onslaught.
Just days earlier, the cruise liner Bremen had been less fortunate.
137 German tourists were aboard when she too faced an awesome wall of
water in the South Atlantic. The impact knocked out all the
instrumentation and all power, leaving them helpless in the tumultuous
sea. Unable to maintain her course into the waves, there was a real
risk the ship could go down and they knew none of the passengers would
survive in lifeboats in such freezing conditions. With emergency power
only, the crew battled to restart the engines. When they eventually
succeeded, it opened the door to a very lucky escape.
"We had said, 'This kind of thing can't happen; this kind of thing is too strange'" |
Al Osborne, wave mathematician |
No current could have created such huge waves. There is none in that
part of the Atlantic. Clearly, there was another effect investigators
needed to find. Except someone already had: it existed (on paper at
least) in the world of quantum physics. Al Osborne is a wave
mathematician with 30 years experience devising equations to describe
open ocean wave patterns. Quantum physics has at its heart a concept
called the Schrodinger Equation, a way of expressing the probability of
something happening that is far more complex than the simple linear
model. Al's theory is based on the notion that in certain unstable
conditions, waves can steal energy from their neighbours. Adjacent
waves shrink while the one at the focus can grow to an enormous size.
His modified Schrodinger Equation had been rejected in the past as
implausible, but with research attention centred on analysing these
rogue waves - including global satellite radar surveillance by the new
European Remote Sensing Satellite - data began to emerge backing his
case. When Al came across the New Year's Day 1985 wave profiles from
the Draupner oil rig, he saw his mathematical model played out in the
real world.
Al's work - if correct - suggests that there are two kinds of waves
out on the high seas; the classical undulating type described by the
linear model and an unstable non-linear monster - a wave that at any
time can start sucking up energy from waves around it to become a
towering freak. The consequences for ship design could be stark.
Currently the biggest wave factored into most ship design is smooth,
undulating and 15m high. A freak wave is not only far bigger, it is so
steep it is almost breaking. This near-vertical wall of water is almost
impossible to ride over - the wave just breaks over the ship. According
to accident investigator, Rod Rainey, such a wave would exert a
pressure of 100 tonnes per square metre on a ship, far greater than the
15 tonnes that ships are designed to withstand without damage. It's no
wonder that even ships the size of the huge freighter München can sink
without trace.