How Dangerous Can Ocean Waves Get? Wave Comparison
12. Dec. 1978. A few hours after midnight, the freighter Marion picked up a distress call from the cargo ship MS München. Several faint SOS signals were received. Apparently the ship, bound for Savannah George, got into trouble crossing the north Atlantic, where a fierce storm had been raging since November. initially nobody was too worried. Only 6 years old at that time the MS München was one of newest and most modern carriers of its time.
It had been designed to cope even with the 10-15m high waves during heavy storms and was widely considered to be unsinkable. Yet when the first recon aircraft in search of the ship flew over the area where it was suspected to be a few hours later they found nothing. What followed was the biggest search and rescue operation ever conducted in the north Atlantic. For one week over 13 planes from the United Kingdom, the United States, Portugal and Germany tirelessly scanned the ocean. Additionally, over 100 cargo ships traveling on the busy shipping lane stopped to participate in the search. And yet, even one week later, when the search was called off, and after combing through an area the size of Mexico, the 260m long ship and the 28 people on board remained lost – Swallowed by the sea as if they had never existed. Merely a few life jackets, a single container and 4 empty life rafts could be recovered. With these few remains, it was of course impossible to determine the cause of the sinking.
Only a lifeboat that was found floating on the ocean almost 2 months later provided some clues. The big steal pins with which it normally was hung 20m – 65ft – above the waterline at the side of the ship showed signs of a huge force striking the life boat. This force had enough power to bend the solid steel bars backwards and tear the lifeboat of the ship.
A wave with enough power to do that would have needed to be significally higher than what scientist at that time thought was possible. The later investigation therefore only concluded that an unusually large wash of water likely broke the windows of the bridge and killed the electronics. The resulting loss of manoeuvrability probably ultimately resulted in the sinking of the ship. Amongst seamen however, rumours went around that a so called Rogue wave also called Monster or Freak Wave was what had caused the ship to sink. For centuries seamen have told tales about encounters with these extreme waves, bigger than any wave surrounding them and so steep they were almost vertical insurmountable walls of water. Given the rarity of credible eye witnesses, as people who encountered those waves usually weren’t coming back to the tale, scientists often dismissed such stories as absurd. They were considered sailors yarn, just like giant sea monsters or mermaids. The mathematical models that long since had been used to describe and calculate the formation of waves simply didn’t allow for such anomalies and certainly not with the frequency sailors reported them. And so the sinking of the Ms München as well as that of dozens of other cargo ships that prior to and after this incident disappeared mysteriously were again and again blamed on technical defects, design faults, or human error.
That at least some of these ships might have fallen victim to a rogue wave, was hardly ever taken into consideration by science even at the end of the 20th century. This all changed with the construction of a new kind of Oil rig in 1994 160 kilometres – 100 km off the coast of Norway. The Draupner platform was the first of its kind and to ensure the safety of the people on board it was equipped with an extensive array of sensors and scanners that tracked among many other things the frequency and height of the waves below. In the night of the first of January 1995 these sensors recorded what should not have been possible: A wave, from trough to crest, 26 meters – 85 ft.
High – more than twice the height of any other wave recorded in the minutes and hours before and after and more than 6 meters or 20ft higher that the hypothetical ocean wave scientists at that time believed would only occur once every 10.000 years. While the Oil rig wasn’t majorly damaged by the wave due to its height minor damage to the underside of the platform confirmed the validity of the reading.
This made the Draupner Wave, as it was later named, the first confirmed measurement of a rogue wave, which meant science finally had to acknowledge their existence. Furthermore it had to be acknowledged that the linear wave models that were till this point used to predict wave height and to calculate the maximum amount of stress ships should be able to withstand fell way short of what is actually possible. Another incident only half a year later made this very clear when the ocean liner Queen E2 en route to New york was hit by a wave 27m or 88ft tall. This is comparable to height of a 9 story building.
The captain later described that it looked as though the ship was headed for the white cliffs of Dover. But what exactly are these Rogue waves? While the terms monster, freak, and rogue waves are often incorrectly used in popular culture to describe all kinds of big waves, scientifically the terms are much more strictly defined. Rogue waves are surface waves. They mostly form in the open ocean and are considerably higher than the surrounding waves. To be regarded as a Rogue wave a wave has to exceed the significant wave height, so the average height of the largest third of the waves, at least 2 fold. By this definition, Rogue Waves don’t necessarily have to be extremely high. Only a lot higher than the average swells at that time. A measurement from a different oil platform showcases this. Here a comparably small 13m or 42 ft. high wave was recorded, that was however significantly higher than the average 3 meter or 10ft high waves during the measurement time frame. Another key feature of Rogue waves is their extreme steepness.
Unlike normal ocean waves that, even when considerable in height, typically rise and fall relatively gently, allowing ships even during big storm to ride them out safely, rogue waves have a very short wavelength for their height and as a result extremely steep flanks. This makes them to insurmountable walls of water that strike everything in their path with tremendous force. Also worth of note is that rogue waves should not be mistaken with tsunamis. A Tsunami consists of a series of waves that move through the entire water column, usually caused by an undersea earthquake or a submarine volcano. Because of this they affect huge volumes of water at the same time but in the open ocean, due their long wavelength of multiple hundred kilometres, you wouldn’t even notice when they pass below you. Only when tsunamis hit the coast, slow down, and get compressed by the rising ocean floor they grow to devastating heights of 10 20 or 30meters. Rogue waves on the other hand arise from typical ocean waves and only affect relatively minute quantities of surface water. They form on the Open Ocean and usually only last for a short time disappearing as swiftly as they appeared.
In shallow waters they would quickly become unstable and collapse, with no real threat of damage to the coast. Far out at sea however, they are Killers that can sink even the most modern ships of today. It is believed that some 25 of the roughly 100-150 super-carriers that were lost between 1960 and 2000 likely have been lost because of rogue waves. Rogue waves are commonly dived into 3 categories. First there are single, giant storm waves that build up to enormous heights and usually collapse after a few seconds. “Walls of water” are wide wave walls that last much longer, traveling up to 10km or 6 miles through the ocean. The last are the so-called “three sisters”. Three giant Waves in close succession. If a ship encounters a considerably high Rogue Wave, one of those that shouldn’t even be possible according to the old models, the consequences are always devastating, and the options for the captain limited. Even if he has enough time to react (which isn’t guaranteed due to the usually sudden appearance of these waves) he can only chose the lesser evil. The risk of sinking remains very real either way. When the vessel is hit from the side, the large surface area of the ship and the amorous energy of the wave can cause the ship to capsize.
When the RMS Queen Mary with over 15000 soldiers on board was broadsided by a 28m or 90ft high wave in 1943 the force of the wave nearly pushed her over on her side. In the matter of seconds the ship listed all the way over to 52°. A scary thought given the ship was twice the tonnage of the titanic. Had the Queen Merry been slightly smaller or rolled another few degrees she would’ve have definitely capsized but miraculously she managed to righten herself. Taking the Wave on bow is also not without risk. The steepness of the waves makes it nearly impossible for large ships to ride them up and down. Due to the inertia of the ship the wave simply slams into it burying it under huge volumes of water. While capsizing is nearly impossible when that happens, it creates another risk: the ship could break apart. When the bow exits the wave on the other side above the next trough, while the stern is still buried within it creates enormous stress on the hull. Ships aren’t built for this kind of point stress.
This much weight unsupported by water can easily cause a ship to break apart as can be seen in the case of the titanic. But this isn’t the only danger a frontal impact presents. Due to the extreme height of rogue waves they usually severely damage the vulnerable superstructure of the ships they strike for instance the bridge. Inflowing water can easily damage the electronics and result in the loss of manoeuvrability. This would turn even normal storm wave into a serious threat. Such a scenario was probably responsible for the loss of the MS München. A similar thing happened to the cruise ship Bremen. in 2001 it was hit head-on by a 35m or 115ft rogue wave that damaged the bridge and knocked out the engines. For 30 long minutes the ship floated uncontrollably through the storm, till the crew managed to turn on a backup engine.
But the most obvious danger of Rogue waves is the tremendous amounts of energy they release upon impact – forces that are beyond any standards used for shipbuilding. A small 3 meter wave has a breaking pressure of 1.5 metric tons per square meter. A 12-metre storm wave would have a breaking pressure of 6 metric tons per square metre Modern ships are built to withstand a breaking force of 15 mT/m² Rogue waves 35meters high however can reach pressures of at least 75-100 mT/m², potentially even up to 500 metric tons – significantly exceeding the limits of what ships are expected to tolerate. These forces have the potential to punch through steel walls like a finger through a potato chip and dozens of wrecks with gaping holes in their hulls are scary reminder of that. But how exactly do these monster waves form? That is something that researchers are still working on.
But a lot of progress has been made since 1995. We now know that rogue waves don’t have a single distinct cause. The basic underlying physics that make rogue waves possible is called constructive interference. This means that waves traveling at different speeds or directions can pile up creating a single huge wave for a short period of time. Many things can cause this to happen. Irregular wind strength and direction, ocean currents or the topography of the ocean floor. In some places the interplay of these factors can create wave focus points – similar to focussing light with a magnifying glass – where the probability of rogue waves becomes much higher.
One of these places is off the coast of South Africa. Here waves travelling northeast from the southern Atlantic propagate into a strong apposing current, the Agulhas current which brings warm water from the Indian Ocean. As a result the waves are focussed and become much steeper and shorter. Abnormally high waves are recorded here frequently and already sunk dozens of ships traveling in this important shipping lane. Additionally, over 50.000 hours of wave data collected from a gas-drilling Platform in South Indian Ocean near the current showcase the frequency and the extreme heights rogue waves can attain here. Over a 6 year period from 1998 to 2003 the sensors recorded over 1500 examples of waves that were roughly 2 times the significant wave height at that time and would therefore qualify as rogue waves.
However they also recorded more than a dozen instances of waves 4-10 times higher than the significant wave height, reaching heights of 30 40 and even close to 50m or 160ft – the height of a 16 story building Because of these finds the Agulhas current is now typically avoided by ships during extreme weather conditions but that doesn’t mean that they are completely out of danger. While these wave focus points significant increase the probability of rogue waves it isn’t the only place where they occur. Many maybe even most Rogue waves form seemingly randomly over the deep sea far away from these spots and can therefore not be explained through these basic wave principles. . To find an explanation for them we have to enter the strange world of quantum physics. This field of science is often counterintuitive and the solutions it presents seem inelegant but nonetheless it gives us a provable explanation for these deep water waves. Through nonlinear quantum mechanical equations it can be shown that it is possible for different wave components to interact and exchange energy without a tangible outside cause.
In rare but still surprisingly frequent cases these interactions can produce an instability that allows a wave to suck energy out of the other waves surrounding it, growing into a rogue wave. These equations can even at least theoretically explain a related praenomen sailors had been reporting for a long time – So called rogue holes. They are simply put the inverse of rogue waves – extreme troughs more than twice as deep as the surrounding ones. Luckily, however, they seem to be a lot rarer than their extrovert sisters. But while this finally allows us out to explain these rogue events it doesn’t bring us much closer to predicting them. And that’s a real problem because as these models as well as real world data shows us, rogue waves are a force to be reckoned with. Only a little over 20 years ago we believed for 3 rogue waves 20m or higher to occur in our oceans you would need to more than 24.000 years. Now we know you probably don’t even need to wait 24 hours. This means it is very likely that every cargo ship travelling the oceans today will during it’s roughly 25 years of service encounter one of these rogue waves.
And if it’s true what we think to know about power of these giants, next to none of them is, despite all our technical advances, equipped for it. .