Mapping Rogue Waves to Protect Vessels at Sea

By Doug Fraser, Cape Cod Times | April 6, 2016

The ocean can be a scary place, with powerful winds and massive swells that wreck the best vessels man can build. But perhaps no single danger is more feared than the rogue wave, which can’t be forecast, and thus carries the element of surprise and tremendous power.

Out of the 127 or so large vessels that are declared total losses each year, one ship, on average, mysteriously vanishes beneath the waves, usually with little or no warning. When that happens, mariners naturally point to a rogue wave -which can be from two to more than eight times the height of the surrounding seas – as the possible culprit.

“They can come from any direction,” said Themistoklis Sapsis, an assistant professor of engineering at the Massachusetts Institute of Technology in Cambridge.

“They occur more frequently than initially believed,” he added.

Sapsis, with funding from the U.S. Navy, has developed a prediction tool he hopes will give mariners, or those working on oil platforms at sea, a two- to three-minute warning before they are hit by a rogue wave. Typically, scientists looking to predict or discover rogue waves use scanning equipment that duplicates every wave within its range, attempting to pick out groupings of waves that fit a profile.

Unlike tsunamis, which travel long distances and are generated by the movement of land, earthquakes or landslides into the water, rogue waves are spontaneous, last for a few seconds to just minutes, and happen when waves pass through one another and combine. If they are traveling in different directions the effect can be momentary, but if the waves are headed in the same direction, they can get quite big and last minutes.

Extreme waves can also develop when their energy is focused, such as when storm winds create waves that run counter to the normal wave direction created by an existing current like the Gulf Stream in the Atlantic Ocean of our coastline and the Agulhas current in the Indian Ocean off South Africa. This can create enormous waves as the distance between peaks is compressed by two opposing forces transferring wave energy upward.

Normally, it would take a number of computers modeling every wave relayed by scanners to find potential rogue waves. It’s slow, expensive, and not practical for shipboard use. Sapsis and co-researcher Will Cousins developed an algorithm – a packet of instructions telling computers what to do – that looks for suspicious clusters of waves running together through the ocean that their research showed tend to exchange energy, potentially creating an extreme wave. The calculations can be handled on one laptop, Sapsis said.

“We try to identify quickly patterns that have a high probability of turning into rogue waves,” Sapsis said. “We are able to predict the occurrence of a rogue wave without having to do the full equation by relying on this algorithm.”

Eugene Terray, a research scholar emeritus in applied ocean physics at the Woods Hole Oceanographic Institution, said Cousins and Sapsis appear to have found criteria for how high the originating waves in a group have to be to trigger the reaction that results in a rogue wave.

Thus far, they haven’t done any testing in the field, but have been working with computer models and experimental data from a wave tank.

“We’ve tried to assess whether this prediction tool gives the same answer as traditional methods,” Sapsis said.

The chaotic proving ground of the ocean is the only real way to know, experts said.

“For something this complex, that is the only way to prove that they have a good and useful technique,” said Bruce Parker, former chief scientist for the National Ocean Service and a visiting professor at Stevens Institute of Technology in New Jersey. Parker also wrote the book “The Power of the Sea: Tsunamis, Storm Surges, Rogue Waves, and Our Quest to Predict Disasters.”

Parker said he wondered how the system would fare in digesting information coming from all directions and not just head on. He was also concerned that two to three minutes may not be enough of a warning.

“It would probably be easier for an (oil) platform, because it is just a matter of turning off some systems and perhaps moving protection walls into place,” Parker said. But turning a large vessel in stormy seas to face a possible threat is both dangerous and difficult to accomplish in just minutes.

“For a ship, it might not be useful,” he said.

Sapsis admitted they still have some significant hurdles, including the development of better scanning technology that can read waves and relay information back to computers on the ship.

“This analysis is very effective for unidirectional waves coming from one direction,” Sapsis said, noting that the lab is a very idealized world that doesn’t take into account many other factors in the real world. He estimated it is at least a few years away from being available to the shipping industry and the Navy.

There’s plenty of incentive to develop a warning system. When wave heights double, from say 50 feet to 100, their power per square foot actually quadruples. While ships are designed to handle heavy seas, the power of rogue waves is estimated to be 10 to 15 times those design criteria.

The shipping insurance industry also is concerned about the size increase in tankers and container ships in recent years, with more length putting stress on the connections between sections, and about the expense of insuring the higher volume of their cargo.

The MOL Comfort, a container ship over 1,000 feet long and only a few years removed from her launching, split in two in moderate seas, burned and sank in June of 2013, with losses estimated at a half billion dollars. In its 2015 review of safety and shipping, Allianz, a major insurer of cargo vessels and tankers, warned of the possibility of a $1 billion loss from the sinking of a single ship.

That pales in comparison with the price tag of the latest Navy destroyer, estimated at over $3 billion.

While many doubted the existence of rogue waves, most have come to accept them, especially after an 84-foot wave was recorded by instruments on a Norwegian oil platform in 1995. In 2007, NOAA Scientist Emeritus Paul Liu compiled a list of over 50 documented “freak wave encounters” by ships and oil platforms stretching back to 1498.

“There’s been a long debate about whether they exist at all, and how you define them, and that’s still going on, although most people feel there are occasional extremely large waves,” Terray said.

While statistical models once predicted such huge waves occurred just once in a 10,000-year span, researchers with the European Space Agency analyzed over 30,000 satellite images of a section of the South Atlantic over a three-week span in 2001 and found what they believed were 10 rogue waves. This was the same area in 2001 where two German cruise ships, the SS Bremen and SS Caledonian Star, were hit by waves they estimated at 100 feet high.

Liu’s list includes the Gloucester swordfish vessel Andrea Gail, which sank with all aboard off Sable Island in the infamous No Name Storm on Halloween of 1991.

More recently, the cargo carrier El Faro sank in 15,000 feet of water last October off the Bahamas as Category 4 Hurricane Joaquin was bearing down on it. Although there was no indication of a rogue wave, the captain reported that a hatch had been blown off by 30-foot seas and the ship had taken on water and was listing with no power. All 33 on board, including two graduates of the Massachusetts Maritime Academy, perished in what seemed a sudden sinking with no mayday call. One of the two lifeboats was found with no one on board.

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