Rogue Waves...something to keep you up at night on long passages - Page 2 - SailNet Community

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  #11  
Old 11-21-2008
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Rogue troughs

Scene: a company Christmas party in Boston many years before we bought the boat. Wife and I are well into our second glass of wine, chatting up a couple who a year before bought their boat. They've just announced they are quiting work in the spring, selling the house, and moving onto the boat permanently. In my wife's eyes, they're experts. The conversation goes something like this:

My wife: "I'm comfortable with coastal trips but offshore makes me nervous. I've heard that there are 'rogue waves' that can swamp a boat".

Jack (the guy who's going sailing): "Awh..., you don't need to worry about 'rogue waves'. You can see them coming and you turn the boat to take them bow on. What you really need to worry about are 'rogue troughs'. They can sneak up on you."

My wife: "Rogue troughs?"

And turning to me, she continues: "You never told me about that"!

Jack: "Oh yea! They're really dangerous!! They're the opposite of rogue waves, but they only occur on flat calm days. You're out there motoring along 'cuz there's no wind, of course --- and all of a sudden... the water drops out beneath you and you fall into the tough. It can swallow a boat in seconds. There's no way to escape."

My wife, looking at me: "I'm not going!"

Me: "Thanks, Jack!"

At the time it was not funny, but Jack and I still laugh about it today.

Jack and Laurie are now in their 10th year of crusing and to my knowledge they've never encountered a rogue trough. For that matter, neither have we.
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  #12  
Old 11-21-2008
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I think after the sea surface analysis satdata came out, they figured there are over 1000 rogue waves--the 100 foot plus kind--out every year.

A four foot wave in a river I'd call a wake or a heavy tidal bore, not a rogue wave.
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Old 11-22-2008
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My wife, Jeanie and I had an "interesting experience" while motoring across a shoal near the 60 fathom line in our day sailor a Marshall Sandpiper. It was flat calm and we were headed for a picnic on Baker Island off Mount Desert Island, Maine. In an instant a large wave rose and broke on us. It hit us bow on and if we had been another 10 yards further out we would have been flipped on our backs. It broke and buried us. Green water hit the mast. It filled the boat and washed stuff out over the transom. That amazing little boat just bobbed up and the motor was still running but the prop was cavitating badly in the foam from the wave. I only had time to say "hold on" and we were under water. A second one followed. That one was not as big as the first but it filled the boat again and washed over the transom. The engine continued to run and no more waves showed up. A small outboard boat was fishing near by and watched the whole thing. I didn't know what to do so I waved and began emptying the boat with a bucket. It was a beautiful day and we made it to Baker Island. It could have turned out very differently. I am now careful to look at inshore charts in this area with an eye for east facing walls that shoal up around the 60 fathom line. That bit of energy could have come from Spain!
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Old 11-22-2008
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That could have been the energy from an underwater landslide or "slump" in the Canary Islands. My understanding is that they aren't always noticed.

There was a documentary a couple of years ago on this, because one of the Canaries is bisected by a fault line and the side facing North America could slide into the abyssal plain, creating a "mega-tsunami" that wouldn't manifest until it hit the east coast (or more properly, the continental shelf) of North America.

Technically, though, there is a big difference between breaking waves, tidal overfalls, tsunamis and rogues. Rogues, I have always understood, are purely wind-driven waves that sync up with other waves and come at you either out of the blue on a flat sea, from an odd direction, and/or as a single, much bigger wave in a series of smaller waves.

I do not get the impression that sea-bed conditions, tides, earthquakes or proximity to land play a role.
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Old 11-22-2008
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I don’t know if they were rogue waves or swell, but crossing the Pacific I did on more than one occasion see much larger humps on the horizon and would watch these move closer. What made these stand out was they were not travelling in the same direction as the prevailing swell and there would only be one or at most three staggered across the sea. They did not have a defined face being more of a hump, the nearest I could describe them would be to use the analogy of an upturned plate lying on the table top, you could feel the power and lift when they went under the boat. Hey, I was there on my own but I did see them; I think.
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Old 11-23-2008
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And you thought you saw mermaids too...

I think the fact that they were in groups of up to three and in a different direction than the prevailing waves makes a good argument for them being rogue swell.

waves=sea state caused by local winds
swell=sea state caused by distant winds, that have travelled to you.

Quote:
Originally Posted by SimonV View Post
I don’t know if they were rogue waves or swell, but crossing the Pacific I did on more than one occasion see much larger humps on the horizon and would watch these move closer. What made these stand out was they were not travelling in the same direction as the prevailing swell and there would only be one or at most three staggered across the sea. They did not have a defined face being more of a hump, the nearest I could describe them would be to use the analogy of an upturned plate lying on the table top, you could feel the power and lift when they went under the boat. Hey, I was there on my own but I did see them; I think.
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  #17  
Old 11-23-2008
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Lenses. Thats what I think rogue waves are all about. Bottom formations curve wave front directions. I'm pretty sure currents do too. If you happen to be in the focal area, you're like an ant under a magnifying glass. All the waves pile up where you are.

Waves travel faster in deeper water. If there's a long mound of less-deep water in-line with the wave direction, then the waves along the wave front will converge -- they will decrease in perceived breadth and gain in height. Somewhere down that mound the waves will pile up. The higher the mound is (in percent of surrounding depth), the less long the mound has to be, and the closer to the mound you'll find the piled-up waves.

I would think that very specific bottom contours could be very effective in converging wave fronts and creating higher waves that would remain converged. This is not the old interference pattern of choppy, higher waves in a specific location only. It is a focusing of the wave that would persist as the wave travelled onward.

Good thing is, with time and computer processing of bottom contours and currents, it ought to be possible to show where these spots are for any given wave direction. And I would think modeling the wave direction from the Canary Islands and other locations of probable underwater landslides would be high on the list.
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Old 11-23-2008
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This is a great thread. My sense is that rogue waves are a perfect example of the chaos theory, where there are so many complex variables and effects of subtle changes in initial condition that it becomes essentially impossible to predict the exact condition at a particular future place and time. It is part of the reason why the weather turns out to be so hard to predict over any long period of time. Take a look at the Wikipedia article on the "Butterfly Effect" for a description.
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Old 11-23-2008
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Quote:
Originally Posted by SimonV View Post
Hey, I was there on my own but I did see them; I think.
I think you did as well, and probably that "rogue swells" are the precursors or the "junior version" of rogue waves.
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Old 11-23-2008
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Rogue Waves

Fellow Sailnet members, who have added their interesting comments and opinions regarding ’Rogue Waves,’ have motivated me to chime in.
First, there is no doubt that rogue waves do exist although I believe the odds of encountering such a phenomenon are rarer than lighting striking people; pirates boarding yachts; shark attacks, or ships sinking pleasure boats. These things do happen but (so far) never to me.

Nevertheless, somewhere in the world’s oceans, rogue waves are building and dissipating at this very moment. How many… is a guess. Some might suggest 5 to 10 while others might say 50 or more. Whatever the true number, it will never come close to the number of ships and fishing vessels that ply the world’s watery highways.

Statistic suggests that just sighting a ship is hundreds, perhaps thousands of times more likely than being struck by a rogue wave. Yet sighting a ship in the vast open ocean is, in itself, a rare event. For example, during my first 35 days at sea as I began my seven -year solo voyages around the world, (while maintaining a watch schedule that was more conscientious than many fully crewed boats. See thread on ‘Kitchen Timers) I saw only one ship. I have never encountered a rogue wave as others describe it in 30 years of being on the water.

During all my time at sea, however, I have, of course, encountered larger than normal waves but calling them ‘rogue’ would be an exaggeration. I once took green water over my boat after being hove-to in a ‘southerly buster’ off the coast of New South Wales, Australia. A large wave ripped out a stanchion in the Red Sea. A 25 footer loomed up above his 18 foot companions in a 50 knot gale off the Venezuela coast and my boat went over the falls and skidded down the wave on her side. However, this was not a rogue. It was the last big roller in the set. All surfers wait for this wave.

So why is their so much chatter about rogue waves? Why do many authors use the term? I think in some cases, while telling these sea stories, it sounds so much more titillating to claim…’ Yes, it was a rogue wave that did me in,’ instead of saying …’ Yep, I messed up. Not paying attention to prudent seamanship.’
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