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Old 28-12-2010, 05:03   #16
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Originally Posted by markpierce View Post
Gee, guys, I'm on deck 6.5, at least fifty or more feet above sea level, and look what's coming!

Cheap photoshop. The glass and grinders sit still on a level table and the lady doesn't give a hoot. Yeah right.

Ordinary effort.
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Old 28-12-2010, 05:09   #17
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That's right. Freak wave stories are horrific and horror sells. Just ask Steven King. Your links prove only that there are some very big waves out there but they may well have been matched by 1000 others in that area on the day.
That's not what people who spend their lives trying to understand and predict these sort of nonlinear events come up with.

New research sheds light on freak wave hot spots

Quote:
In a normal wave field, on average, roughly three waves in every 10,000 are extreme waves," Janssen said. "In a focal zone, this number could increase to about three in every 1,000 waves. In a focal zone, the average wave height is already increased due to the focusing of energy so that an extreme wave in such a high energy area can potentially be very energetic and dangerous."
The Journal of Physical Oceanography is hardly in the business of selling horror stories.
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Old 28-12-2010, 05:11   #18
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Ship-sinking monster waves revealed by ESA* satellites

Once dismissed as a nautical myth, freakish ocean waves that rise as tall as ten-storey apartment blocks have been accepted as a leading cause of large ship sinkings. Results from ESA's ERS satellites helped establish the widespread existence of these 'rogue' waves and are now being used to study their origins.

Severe weather has sunk more than 200 supertankers and container ships exceeding 200 metres in length during the last two decades. Rogue waves are believed to be the major cause in many such cases.

ESA Portal - Ship-sinking monster waves revealed by ESA satellites

* ESA: European Space Agency
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Old 28-12-2010, 05:11   #19
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Cheap photoshop. The glass and grinders sit still on a level table and the lady doesn't give a hoot. Yeah right.

Ordinary effort.
Sorry. You're ignorant because that photo is untouched, and obviously you haven't experienced the power of the oceans.
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Old 28-12-2010, 05:21   #20
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Sorry. You're ignorant because that photo is untouched, and obviously you haven't experienced the power of the oceans.
If you did not take it then you cannot make that assertion. Waves 1/4 the size of those alleged would have caused the glass and shakers to fall. Additionally, the angle of view is sharply down thereby making the apparent size of the wave appear greater. The table must be close to level or the shakers would have fallen.

What evidence do you have to justify the use of "obviously"?
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Old 28-12-2010, 05:27   #21
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That's not what people who spend their lives trying to understand and predict these sort of nonlinear events come up with.

New research sheds light on freak wave hot spots



The Journal of Physical Oceanography is hardly in the business of selling horror stories.
There is nothing freak about a big wave near a sudden decrease in water depth. That is totally predictable. You can see it on every river bar.
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Old 28-12-2010, 05:27   #22
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Subsequent to that photo, a bowl of milk fell onto my lap, several people fell with their chairs, tableware and plates fell on the floor, etc. And later I fell on my back, wrenching my left knee and still sustain up to a "four" in pain. I'll remember those who don't believe me.
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Old 28-12-2010, 05:33   #23
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If you did not take it then you cannot make that assertion. Waves 1/4 the size of those alleged would have caused the glass and shakers to fall.

What evidence do you have to justify the use of "obviously"?
My LTGF took that picture. You don't believe what you see, probably because you haven't really experienced the sea. It's as simple as that. And you hide behind a false identity, unlike me.
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Old 28-12-2010, 05:52   #24
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There is nothing freak about a big wave near a sudden decrease in water depth. That is totally predictable. You can see it on every river bar.
Well it might be best to define each othgers position on this.

Yours seems to be that the extreme events being discussed here are simply 'more of the same'. Linear waves but just big ones.

I don't buy that, I'm siding with the non linear view, once in a while conditions can exist to produce something less common which doesn't behave in the way that is predicted by the maths models which work for the rest of the waves.

Usually what happens now is a contest of "my google search results are better than yours"

Take 1...

Quote:
Abstract

In a statistical description of ocean surface waves, the occurrence of extremely large waves is expected, but with low probability. In narrow-band, unidirectional waves it has been shown that the random-wave equivalent of the Benjamin-Feir instability results in an increased likelihood of extreme events (high kurtosis values) through near-resonant cubic interactions. Recent findings indicate however that freely developing directionally-spread waves do not develop such non-Gaussian features. Instead, the wave field returns to a near-Gaussian state, which is also what is invariably observed in field observations. However, ocean waves, and in particular on the continental shelf and near the coast, are not necessarily freely developing. To investigate the effects of medium inhomogeneities due to currents and topography on the nonlinear wave statistics, we consider the concomitant effect of refractive focusing and nonlinearity. Thereto we develop a spectral nonlinear evolution model and perform Monte-Carlo simulations of waves traversing a refractive focal zone. Simulations show that narrow-band directionally spread waves can develop instabilities when traversing a refractive zone, resulting in strongly non-Gaussian features (high kurtosis) locally. We will present our modeling approach and principal simulation results, and discuss the implications for ocean wave statistics. This research is supported by the Office of Naval Research (Coastal Geosciences and Physical Oceanography).
I've no idea what he's talking about either but he sounds like he knows much more than 'freak waves are made by lazy journalists'.
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Old 28-12-2010, 06:11   #25
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Well it might be best to define each othgers position on this.

Yours seems to be that the extreme events being discussed here are simply 'more of the same'. Linear waves but just big ones.

I don't buy that, I'm siding with the non linear view, once in a while conditions can exist to produce something less common which doesn't behave in the way that is predicted by the maths models which work for the rest of the waves.

Usually what happens now is a contest of "my google search results are better than yours"

Take 1...



I've no idea what he's talking about either but he sounds like he knows much more than 'freak waves are made by lazy journalists'.

All he is saying is that when an onshore current strikes an underwater cliff or slope the water has nowhere left to go but up. The waves at that place will be bigger. Nothing freakish there just lots of big words by the quoted author. You get a similar effect when two currents run down opposite sides of a headland and meet off the point. The excess water has nowhere to go but up and the waves get bigger. Nothing freakish there either.

Study Marshallese navigation sometime and put all this stuff to your advantage.
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Old 28-12-2010, 06:26   #26
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Old 28-12-2010, 06:40   #27
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Rogue waves are a well researched and clearly defined phenomenon. The scientific evidence is pretty conclusive. Savoir doesn't believe the scientific evidence, or chooses to ignore it. Fine. We aren't going to change his mind. He isn't going to change our minds. Time to let it go.
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Old 28-12-2010, 06:50   #28
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I don't think my freak wave story meets the classic definition, but...

We were on the last few hours of a 5 day passage from Georgetown Bahamas to Boquerone PR. The previous 24 hours were with a strong north wind from behind us, I think about 30 knots, and we were steadily surfing along between 9 and 10 knots.

The waves were large, but because we were riding along with them, no big deal. I would describe it as a very long ocean swell with a nasty surface chop, but NO large breaking waves. On other points of sail, and discounting the "swell" aspect, I'm pretty good at judging the wave height. Not so regarding a long ocean swell. I just know that in the troughs, my view was more or less the sky.

Our Searunner 34 Tri has a huge centerboard with skeg/rudder, and was totally under control in these conditions.

Well into the Mona Passage, and approaching landfall, the boat encountered a wave that was not at ALL like the pattern around us. The boat rose way up for a second and then the huge wave that was under us, (but we never saw), broke right out from under us!

The decks remained horizontal at first, and then the boat just DROPPED straight down for a second or two. (I felt very nearly 0 Gs). Then with us still on autopilot, it pointed down the mountain, reacted too slowly at the bottom, and threw me across the cockpit. I did not get to the wheel in time, and we broached... BIG TIME! We healed so far over that I thought we might capsize. Then she straightened up and once again, took off. I was shaken... and stirred.

I was very appreciative of Jim Brown's concept of keeping the 25% payload down very low and in the middle third of the boat. It saved our bacon!

After going below & studying the chart, I realized that we had just crossed an underwater hump with only 60' over it. The surrounding water being VERY deep, a strong current in a narrow passage, high winds, and huge swell, were the perfect combination.

If I had paid more attention to the soundings, I would have gone around this hump. It was a set up!

As I said, this is not the classic definition of a rogue wave, as it was generated partly by bottom conditions, and probably did repeat itself, in that one spot only.

I have however been a multihuller for decades and studied the subject in my own self interest. I assure you that rogue waves are for real, and as far as their existence is concerned, the jury has been "in" for over 25 years. They scare me as much as floating containers must scare monohullers! In both cases, what you can do about it is "be lucky".

Since multihull capsizes usually result in survival of the crew, this is where the largest volume of accounts are. They lived to write it down. One of the best is the account by Phil Weld in "Gulf Streamer". After his 60' tri was tossed in the air and flipped by a huge rogue wave on a moderate sea, he had a new tri built called "Rogue Wave". It is a good story for those interested in rogue waves.

Mark
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Old 28-12-2010, 06:52   #29
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Dunno about underwater cliffs and opposing currents.... I find the worst are the wind created waves.....
Usually found after a lunch of a tin of baked Beans and sausages on toast......


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Old 28-12-2010, 06:57   #30
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Dunno about underwater cliffs and opposing currents.... I find the worst are the wind created waves.....
Usually found after a lunch of a tin of baked Beans and sausages on toast......

--its that prevailing southerly thats a real stinkin' breeze.
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