Mystery of monster waves solved

GERMAN scientists claim to have explained the mystery behind so-called monster waves - the term given by oceanographers for near-vertical breaking seas up to 120ft high. Such seas are thought to have sunk more than 200 supertankers and container ships without trace during the past two decades.

Often dismissed as sailors' yarns, monster waves have terrified seafarers for centuries and provided the raw material for countless novels and films including Sebastian Junger's recent best-seller The Perfect Storm.

Yet until now scientists and oceanographers had been unable to determine exactly what formed such gigantic "one-off" seas that are capable of breaking a 600ft-long ship in half and sending it to the bottom within seconds.

A team of oceanographers at the Technical University in Berlin has now managed to explain the phenomenon with the aid of computers and by simulating monster waves in a tank.

"Our wave experiments have proved for the first time that monster waves are physically possible and that they really do exist," said Prof Gunther Clauss, who led the team of scientists.

"This represents a breakthrough for the shipping and oil industries because we can now start to design structures that can cope with these monsters," he added.

Using a computerised, hydraulically powered wave-making machine in a specially designed tank supplied by oceanographers at Hanover University, Prof Clauss's team has established that monster waves can occur with little or no warning.

The waves are created in a storm when slow-moving waves are caught up by a succession of faster waves travelling at more than twice their speed. "What happens then is that the waves simply pile up on top of each other to create a monster," said Prof Clauss.

"The result is an almost vertical wall of water which towers up to 120ft in height before collapsing on itself. Any vessel caught by one of these has little chance of surviving."

Photographs of the experiments show the monster wave building into a vertical wall of water before exploding into an uncontrollable boiling mass as it collapses on itself.

"Even in the tank the effect was awe-inspiring," said Prof Clauss. "The exploding wave was so powerful that it broke through the ceiling of the building in which the tank is located," he added.

Monster waves are thought to have caused the loss of at least 200 "super carriers" or ships measuring more than 600ft in length on the world's oceans over the past 20 years. The unexplained disappearance of many smaller vessels including trawlers and yachts could put the total number of losses much higher.

Yet accounts by seamen who have witnessed such waves are comparatively rare. One, dating from 1995, was when the QE2 was hit by a hurricane on a crossing to New York.

She survived what was estimated to be a 95ft high wave which the ship took directly over her bow. Her captain, Ronald Warwick, described the phenomenon as "like going into the White Cliffs of Dover".

One of the few small-boat sailors to survive a monster wave was the British yachtsman, Brigadier Miles Smeeton, who did so twice. His 50ft ketch, Tzu Hang was dismasted twice by such waves while attempting to round Cape Horn in the 1950s - once after being "pitchpoled", toppled stern over bow.

In Germany, the horrors of monster waves have been brought right up to date after revelations about the near-sinking of the German Antarctic cruise liner Bremen in the south Atlantic last year. The ship with 137 passengers aboard was hit by a 114ft wave in March while heading towards make Rio de Janiero after an Antarctic cruise.

The impact smashed windows on the bridge and cut the ship's electricity supply. The vessel drifted engineless for more than half an hour heeling at an angle of 40 degrees in huge seas whipped by hurricane-strength winds.

"I have been at sea for 48 years, but never have I experienced such a wave," said the Bremen's captain, Heinz Aye, 65, who is now retired.

Prof Clauss said that his team's research would help naval architects in their efforts to construct ships and oil platforms that were capable of withstanding such freak wave forces.

"In many cases it is as simple as building a bridge on a ship that is not slab-sided but rounded, so it can cope with being hit by a monster wave. Most ships plying the oceans right now are not built along these lines," he said.

The team also hopes that its research will help in the development of radar that is specifically designed to warn of sea conditions that could produce the monster-wave phenomenon.

"This could help the captains of ships to steer clear of a danger area, but the truth is we can do nothing to prevent monster waves. They are a product of nature," Prof Clauss added.

ROGUE WAVES

An existence as ephemeral as a mayfly but savage enough to sink a modern ship.

by Charles Thrasher, Bluewater staff

Bluewater's Newsletter #7 - Waves, wind & weather : Rogue Waves

The imaginative cartographers of the Middle Ages labeled much of the Atlantic the "Sea of Darkness" and warned mariners: "Here there be monsters." The oceans are mostly charted now and imagination has succumbed to knowledge but the monsters remain; brief, fleeting beasts with an existence as ephemeral as a mayfly but savage enough to sink a modern ship with a single blow. Rogue waves. Even the name connotes rampage and destruction like the charge of an outcast elephant. Like the rogue elephant, their appearance can be abrupt and devastating.

A rogue wave is the coincidence of several wave trains, the crest of one train superimposed and amplifying others. The typical life span of a rogue is measured in seconds. Abruptly they heave themselves above the surrounding waves and abruptly they dissipate, but within that brief span of coincidence a rogue can rise to monstrous heights.

The existence of a rogue wave is predictable only as a statistical probability - the percentage of probability that a wave of a specific height will occur within a specific area during a specific period of time, typically a period of years. That's not much comfort for a sailor looking warily over his shoulder for the sudden onslaught of a rogue. One thing is obvious: big seas breed bigger rogues. And the seas are getting bigger.

For the last 20 years a British ship has been anchored off Land's End, Cornwall, its crew patiently measuring the heights of endless waves. In those 20 years the average height of storm waves buffeting the anchored ship has risen from 39 feet to an intimidating 57 feet. (God alone knows how they manage to keep a crew onboard.) More typical wave heights have increased from 7.4 feet to 9 feet. The cause of this increase is still unknown.

How big are really big waves? In 1966 the passenger ship Michaelango was struck by a wave that stove-in ports 81 feet above her waterline. The bow section was flooded and three passengers killed. In 1965 the heavy cruiser USS Pittsburgh had 90 feet of her bow torn off by a wave. In 1933, the U.S.S. Ramapo reported the largest wave ever accurately measured at sea - 112 feet. The largest wave until Halloween, 1991.

It was the storm expected once every 10,000 years. A low-pressure system stalled off the coast of Nova Scotia. All the elements necessary to create massive waves were present - a wind of 70 knots blowing across unobstructed water for a prolonged period. These elements - wind strength, fetch and duration - resulted in waves reliably measured at 150 feet! Over a thousand miles away the residents of Melbourne, Florida gathered on their boardwalk to watch 15 foot surf thunder against the shore.

Oddly enough, the strongest winds don't create the largest waves. Winds in excess of 70 knots begin to topple waves and 100 knot winds will flatten them. Wind, however, isn't the only force that can make a wave dangerous. A strong current running opposite the direction of wave propagation can both heighten and steepen waves. There is a place off the pitch of Africa where a strong opposing current, huge waves and heavy shipping traffic intersect. It's a place where ships are known to vanish silently with all hands.

I mentioned hat the height of a wave is determined by three factors - wind speed, fetch and duration. In the Southern Ocean the fetch is almost endless, encircling the entire planet. The waves generated by that ocean are formidable. When the powerful Agulhas Current opposes these waves, the results are phenomenal.

The Agulhas Current is similar to the Gulf Stream and the Black Current (Kuroshio) of Japan. All are western boundary currents, among the most intense of ocean currents. The Agulhas can attain a velocity of eight feet per second driving south along the eastern coast of South Africa. When it rounds the Cape of Good Hope, the current is channeled by the steeply sloping continental shelf of Africa into the prevailing westerly winds of the Roaring Forties and their attendant waves. A strong current suddenly opposes large waves driven by relentless winds across a vast ocean. Conditions are ideal for the formation of rogue waves of staggering height.

A breaking wave can exert considerable pressure, as much as one ton per square foot. Imagine the damage resulting from a 100 foot wave breaking on the bow of a modern ship. She can founder, her buoyancy negated by the weight of water shipped on deck, or her bow can be holed. But at least a rogue wave is something a watch officer can see, and perhaps take steps to mitigate the damage.

The most alarming rogue may not be the crest at all but the trough. Where the troughs of numerous wave trains coincide, huge holes may suddenly appear in the ocean. Rogue troughs are secretive beasts and rarely seen. Their inverted profiles make them even more elusive than rogue waves. A ship's bow may fall into an enormous hole without warning. Driven by gravity and momentum, the bow may dive so deep it never rises. A modern ship with all the imaginable safeguards can go down before there is time to broadcast a Mayday.

Not all rogues are monstrous and alien. You can find them in your bathtub or the Intracoastal Waterway. Waves reflected from a vertical surface (like the sides of your bathtub or the concrete bulkheads that often form the banks of the ICW) lose little of their energy. Recent research indicates that when the crests (or troughs) of both the original and reflected wave are exactly synchronized, even though they're traveling in opposite directions, a wave can result that's taller than the sum of the individual waves. In other words, a true rogue. Rogues are likely to form in the lee of islands where waves, refracted by the island, rejoin at an acute angle.

There is at least one thing easily learned from the study of rogue waves - avoid the conditions likely to create them, especially a strong current running contrary to heavy seas. One excellent example is the Gulf Stream during a strong northerly wind. The actual danger in such conditions may be much greater than you might assume from a marine weather report.

Many years ago I was on a jack-up drilling rig on the edge of the continental shelf in the Gulf of Mexico in about 200 feet of water.
Hurricane George, which turned and hit Mexico, blew across our rig.
All hands were evacuated by boat early in the day because of the lack of helicopters, but someone had to operate the crane to lower people to the work boat so the tool pusher, the mechanic and myself stayed to ride it out.
By nine that night the wave height measured from the legs on the jack-up was over forty feet.
The wind gauge in the wheel house showed gusts of over seventy miles per hour.
We had a sixty foot air gap, but some of the waves were hitting the bottom of our hull.
The giant LeTourneau jack-up was doing a Watusi dance, and cracks began to appear in the floors of the galley and living quarters.

The sweetest sound I've ever heard was the two-way radio when it crackled to life asking our location for an emergency evacuation by a big Puma flying on radar.
The Puma couldn't land; he could only hover for a short time.
We crawled across the landing mat and jumped up into the helicopter one at a time as he made successive passes trying to time a calmer period when he could approach.
The thing I remember most clearly was that the sea was not black; it was solid white!

When we got back to the rig several days later, we could see the damage the waves had done to the items on our upper deck which was forty feet thick.
In other words, the wave height had to exceed the sixty foot air gap plus the forty foot hull depth to reach our upper deck.
The wind gauge in the wheel house was broken at 110 miles per hour.
Amazingly, the rig itself was virtually undamaged except for cracks in all the floors.

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