Understanding “Freak” Waves Dag Pike
Wild storms make for wild seas, and for hundreds of years sailors have returned to harbor with tales of encountering huge waves in the ocean. They may be called rogue waves or freak waves, but these are really extreme waves that deviate dramatically from the regular wave pattern. Once considered to be the product of imaginative sailors’ minds, extreme waves earned credibility as authoritative reports started to emerge. Dramatic photos reinforced the reports. Today, sophisticated wave-measuring technology and satellite observations help detect these waves, and a 100-foot monster wave has now been experienced—and verified—in the Atlantic.
For the cruising skipper, rogue waves are something to take into account when planning a passage. Calculations from the British National Institute of Oceanography, using a random process formula, suggest that if you take the average height of waves in a train, 1 in 23 waves will be twice the average height, and one wave in 1,175 will be three times the average height. While those figures might give sailors pause for thought, the additional chilling statistic is that one wave in 300,000 will be four times the average height of the wave train. Think about that—you have the prospect of meeting a 60-foot wave when the average height is just 15 feet. However, to put this into perspective, 300,000 is an awful lot of waves, and that equates to only one extreme wave of that size every 6,000 miles. Even then, extreme waves tend to occur only in conditions that you will have tried to avoid anyway. In 65 years at sea, I have experienced three rogue waves, and these monsters appeared only during winds of gale force or stronger.
I experienced one of these rogue waves during a hurricane in the Caribbean. This was in the 1950s when hurricane warnings were not up to modern standards and forecasting the track was often difficult. Our 6,000-ton freighter got caught up in this maelstrom of wind and water as we were approaching Sombrero Passage in the Lesser Antilles, and we had plenty of sea room to cope. We didn’t see the monster wave that appeared out of the hurricane, only its aftermath— two of the ship’s metal lifeboats had been flattened against their davits and the funnel damaged. It must have been a big wave to ship solid water 30 feet above the waterline.
Another scary moment was when my crewmates and I were searching for a fisherman who was reported washed off the rocks in the Bristol Channel on the west coast of the United Kingdom. We were in a brandnew lifeboat being delivered to its station and were on passage along the coast in a Force 7 gale, looking forward to getting into harbor. The Coast Guard hailed us on the radio to ask us if we would assist in the search. My plan was to run parallel to the shore, just outside the surf line where a big sea was breaking in the northwesterly onshore gale. Though we would have gone inside the surf if we had seen something or someone to rescue, the risk was too great during the searching period. As you can imagine, all eyes were turned toward the shore to look for the man in the water. I was at the helm and watching toward shore as well when I was suddenly conscious of a looming darkness. I looked to seaward and saw a towering wall of water rearing up alongside us with the sun shining weakly through it.
This nearly vertical wall of water seemed poised to curl over and crash down on us, and it was too late to do anything but pray. We went up the side of that wave like an express elevator and toppled over the crest just as it broke, narrowly escaping from a capsize that would have washed our self-righting lifeboat
onto the beach. I estimated that breaking wave at three or four times the average height of waves that day, and so it had been just starting to break in the deeper water outside our path.
The third extreme wave I experienced was found to the north of Iceland during the Cod Wars, a series of disputes between the United Kingdom and Iceland regarding fishing rights. Our big oceangoing tug was there on escort duty, protecting the British trawlers from the Icelandic patrol boats. We were running before the big storm seas that are a frequent winter experience in the region—indeed it is a good day up there between Iceland and Greenland when it is only blowing Force 8. I was down on the low afterdeck trying to get some good photos of the rough sea, and I remember watching these waves curl up behind us and then pass under the ship in a regular procession as I clicked away. Then, out of the blue came a rogue, rearing up and topped by a curling white crest. It was like a vertical wall of water with the crest likely 40- to 50-feet high. I took a quick photo and then ran for shelter as it crashed over the stern and swept over much of the forward superstructure, half submerging the ship. Thank goodness for a tough ship.
Others have experienced much bigger waves than I have, though. A weather ship off the coast of Norway recorded a 90foot wave. The officer on watch, Jan Erik Taule, tells the story: “It was shortly after midnight, 11th of November 2001, that the 54-meter long MV Polar Front encountered a 27.2-meter (89feet) wave in position N65˚ 55 E002˚ 03. For the last couple of days, the wind had been steadily WSW with gale force. The 10th of November the wind increased to storm Force 10 and on into hurricane force, 56 knots with gusts to 75 knots. At midnight 11th of November, I released the captain at that time, Børge Misje, and got briefed about the weather conditions and [especially] the extreme height of the sea, which [had] raised to 18-22 meters. The ship log says at midnight—wind force 55 knots from W with snow and showery weather. In spite of the showery weather condition, it was a kind of bright night due to the moonlight between the showers.
“I was sitting in the chair, having my coffee, when suddenly I saw a heavy sea rising in front of the ship, some distance away, and knew that this would be a nasty one. It [looked] quite scary in the moonlight with a lot of foam on top of the wave. I switched from autopilot to manual steering and at the same time gave more engine power, trying to meet the monster dead ahead. Luckily I [managed] to do so, and the wave lifted the ship bow in an abnormal angle. I felt that the vessel might have a problem climbing the wave and gave full ahead forward. The vessel climbed slowly and suddenly the air was filled with a roaring noise and the air was nothing [but] foam all around us. The ship [shook] and vibrated a lot when the propeller lost the water at the top of the wave. I myself was standing on my feet and [grabbed] my hands around the steering wheel, afraid of falling. ‘Damn it’ was the only thing I could say when the ship was over the top and started falling down the other side of the wave. I felt myself hanging in the air and could hardly stand on my feet when the ship bow crashed into the next wall of water. The force of gravity was unlike anything I ever felt before.
“The seawater smashed to the front of the vessel and found the way into the accommodations through different air outlets. There was no damage to the vessel itself, but in [the] cabins, galley, and other areas, furniture and loose parts were a mess. The crew itself took the incidence calmly—just another nasty bastard. That’s all there is to say about it. Laying out here in the middle of the track from Atlantic lows is a rough job, but a man gets used to whatever comes.”
The 90-foot freak was measured by a wave-height recorder aboard the Polar Front, and a similar device was fitted to the research ship Discovery when she encountered the first 100-foot wave ever recorded from a ship. Dr. Penny Holliday, a scientist, was on board at the time and recounts the experience:
“I wasn’t asleep—no chance of that when your bunk appears to be trying to throw you out of it. I was trying to stay wedged into [my bunk], with my lifejacket stuffed under one edge of my mattress and feet jammed against the wooden sides at the bottom. But there was no sleep. It was very noisy, as you can imagine. As well as the sound of wind and the sea crashing onto the side of the ship and swishing down the decks, I could hear general banging and crashing all around. The ship creaks and groans, and as it flexes the fittings [it] makes a kind of ‘he-he-he’ noise, which in the middle-of-the-night-paranoia sounds like your wardrobe is
laughing at you! At some point the chair in my cabin flew across from its position under the desk—where I thought I had carefully wedged it tight—bounced on the floor and jumped on top of me. So some of the time I was trying to sleep, and some of the time I was just lying awake hoping things would improve.
“I couldn’t honestly say I felt the biggest wave and knew what had happened, but during that night we had 23 waves that were over [65 feet], and I certainly could tell that this was no ordinary storm. I’ve been through some very bad weather several times before in the Rockall Trough and in the Iceland Basin—my worst previous [weather] being in 1996 when we had significant wave heights of about 13 meters south of Iceland. But the violence of the motion and the obvious very deep concern of the captain, engineers, and bridge officers was something I certainly hadn’t known before.
“A particularly alarming event happened the night after the biggest waves, when the storm was still raging but the waves had decreased a little. During the night, the starboard lifeboat came loose after a roll of about 35° and was banging against the side of the ship. The noise of each bang was tremendous—somehow made worse by it being about 4 am. Some extremely brave crew were dispatched to secure it until daylight and calmer seas. In many ways, this was the most frightening thing for me to see— the bosun and ABs having to go out into that weather to do a very dangerous job. I think that was when the seriousness of our situation was brought home to me. Wanting to keep out of the way, I stayed in my bunk, listening as the men with harnesses and equipment clinking, opened the watertight doors outside my cabin. I think I held my breath for most of the time they were out there. But they did the job and came back.”
The Discovery was operating in the Rockall Trench, an area of deep water that lies between Iceland and the Shetland Isles. On the night in question the weather map showed the isobars lying west to east almost right across the Atlantic in a straight line. This created a fetch of over 1,000 miles for the waves to develop, and the recordings were showing consistent waves of over 60 feet with the winds blowing at around 50 knots. The 100-foot waves are thought to have developed ahead of an active front that was traversing the area. The theory is that the extreme-wave instances were created by resonance from this frontal system which focused and boosted the energy of the waves to create the monsters.
What causes these extreme waves? One of the latest theories relates to deep depressions. The bigger a wave is, the faster it travels, so when a depression is deepening there are smaller and slower waves being generated at the beginning, which are followed by larger and faster waves. When these larger waves catch up with the slower ones and the two crests combine, you can get a rogue wave. Another possible cause is when two or more wave trains cross. Once again, you get the combined height of the two waves, and this will tend to cause the type of rogue waves that some have described as a pyramid. In both instances, the rogue wave will be transient, appearing and disappearing as the crests combine.
Satellite detection is a new tool used in the study of extreme waves and has led to an increased knowledge of rogues and their reported frequency. Under a program known as MaxWave that is funded by the European Commission, satellite detection of extreme waves has shown that not only do these wave constructs occur more frequently than previously thought, but that they occur in most regions (even in fresh water). However, the increased detection frequency could also be the result of a revised specification for what constitutes an extreme wave. The MaxWave program classifies an extreme wave as any that measures twice the significant (or average) wave height. Any sailor will tell you from experience that waves of this size are a frequent experience, and as previously mentioned, they generally occur once every 23 waves. What we commonly understand as rogue waves, however, are truly extreme waves—much larger than this basic definition.
We talk about wave height in relation to rogue waves, and this tends to evoke a picture of an extreme wave towering above the median sea level. But wave height is the distance between the trough and the crest, not the median line and the crest. And what is interesting about the recordings of that 100-foot wave experienced by Discovery is that the distance from the trough to the median line was larger than the distance from the median line to the wave crest. Though you may picture a ship trying to climb over the huge crest of an extreme wave, in reality the chances are that it is the deep trough that comes either before or after the high crest that does the damage. These deep troughs— or “holes”—are like the reverse of an extreme wave. When a ship falls into them, its chances of climbing out unscathed are small. At this point, the ship is vulnerable, and the following wave can deposit tons of water on the deck to cause serious damage. This is what happened to the Polar Front. While there is a chance that you might see an extreme wave crest some way off, so that you have time to do something about it, you don’t see one of the holes until you fall into it—and by then it may be too late.
These holes exist in many types of sea conditions, and there are many tales of ships and boats being affected by them. I found one myself when I was testing lifeboats during the dangerous Portland Race off England’s south coast. This race is notorious for wild, breaking crests created when strong tides meet shallow water in a gale of wind, the perfect extreme conditions to test a lifeboat’s performance in rough seas. We went over the first breaking crest quite happily, but then there was a hole on the other side. The entire boat became airborne and dropped into the hole where I swear you could almost see the seabed. And then the next wave fell on top of us. I was so grateful we were in a strong boat, and we eventually rose clear with only superficial damage. But the scary part of that encounter was the total lack of warning.
Many yachts have reported encounters with large waves, and of course we only hear from those that have survived. It would seem, though, that small boats have a better chance of survival. Smaller boats lift and fall to the waves while large ships tend to batter their way through them because they are less buoyant, and this is what can cause severe damage.
Although statistics are hard to come by, it seems reported encounters with extreme waves have been relatively rare. The MaxWave program suggests that more than 200 large ships have been lost to rough seas and severe weather over the past 20 years. Whether this is due simply to rough seas and the damage or mechanical failure that contributed to the sinking is not clear, but the actual number of recorded encounters with extreme waves is much lower. Weather ships that have been cruising in the open North Atlantic on a continuous basis have recorded waves of up to 75 feet in height, and you might expect that if these extreme waves were a frequent occurrence, the weather ships would have experienced them. Most of the weather ships have now been replaced by recording buoys that are equipped with monitoring equipment that sends continuous reports on weather and sea conditions. During some of the major storms that have occurred off the coast of North America, these buoys have recorded waves of over 80 feet. And because these waves are associated with violent storm conditions, it is thought that they are transient peaks created in the confused seas. The buoys tend to be moored in relatively shallow waters, though, and this is likely to increase the height of the waves compared with those in open water.
As more of these extreme waves and holes are recorded, we are starting to get a better picture of three distinct types of extreme waves that occur. One is the “three sisters” type, where the wave is one of three very large waves, and it is suggested that these are created by a secondary wave train being superimposed on the more regular waves. This may be the type of wave that the Discovery experienced. A second type is the “wave tower,” a sort of pyramidshape wave that exists as a single peak and could be created, in part, by current causing large wave trains to cross each other at a shallow angle. Finally, there is the “white wall,” a huge wall of water that appears vertical with its crest starting to break. Several yachts and ships have reported this type of extreme wave, and it must be one of the most frightening experiences of a life at sea. n\