Un­der­stand­ing “Freak” Waves Dag Pike

Passage Maker - - Contents - BY 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\

Thanks to mod­ern data col­lec­tion at sea and via satel­lites, we are start­ing to de­velop a sci­en­tific un­der­stand­ing of rogue waves. 44 pas­ July/Au­gust 2017

Be­low: The chart be­low is a graph­i­cal rep­re­sen­ta­tion of one of the first recorded rogues, called the Draup­ner wave that hit an oil rig on the North Sea. It is said to be the first rogue wave in­ci­dent to be recorded and ver­i­fied.

A 1943 pho­to­graph of a large wave break­ing over the islet of Rock­all, in the North At­lantic Ocean. Rock­all’s peak is about 56-feet above sea-level, and the height of the spray has been es­ti­mated at about 170 feet.

This Photo: Run­ning in 25-foot seas in Valdez, Alaska, this tanker en­coun­tered a rogue 60-footer, shown here, hit­ting the tanker broad­side. Above: A graph shows a se­quence of rogue waves, in­clud­ing “holes” as deep as 55 feet.

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