Roque Waves

[kmacdonald]

Rogue waves are thought to be very short lived waves. 5 or 10 minutes before they dissipate.

[GordMay]

You might be interested in some of our earlier discussions:
Rogue Wave Prediction ➥ https://www.cruisersforum.com/forums...on-287891.html
The Rogue wave and the sailor ➥ https://www.cruisersforum.com/forums...-222856-3.html
Rogue Wave Study ➥ https://www.cruisersforum.com/forums...dy-181348.html
What, really, is a rogue wave? ➥ https://www.cruisersforum.com/forums...-241381-2.html
The Grand Unified Theory of Rogue Waves ➥ https://www.cruisersforum.com/forums...es-230153.html
Yikes! Rogue Waves ➥ https://www.cruisersforum.com/forums...ves-31117.html

[Talbot]

A much bigger problem than trains of waves of different wavelengths creating a big wave when they peak together, is when you have a series of storms each creating their own wave train, but they are coming from different directions. The resultant peak wave when they all coincide, can be devastating as not only are they sudden and almost impossible to predict, but they can be very very steep and slam into the ship's side from an unexpected direction. I have seen TV of this occurring off the Alaska coast, and tipping a large fishing vessel right on its side - they were very lucky to survive.

[Nicholson58]

In wave action two or more wave crests always combine to form a sum. It doesn’t matter the direction. Three from 120 degrees apart will make a spike. Similarly, a crest and a trough cancel. The phenomenon is called constructive and destructive interference. Waves that split around an object such as an island will both turn in towards one another and form an interference pattern. The same is true for EM waves. This results in picket fence reception on the AM band.

[Breaking Waves]

Originally Posted by massnspace

Nothing is unpredictable in the world of particle physics….nothing.

hhmmm . . . . . .the 'simple' 3 body problem would like to enter the discussion, as would any system with chaos component...

[keelbolt]

Interesting quantum mechanics perspective on rogue waves. Put on your physics hat...

https://physics.aps.org/articles/v12/146

[Talbot]

Originally Posted by Nicholson58

In wave action two or more wave crests always combine to form a sum. It doesn’t matter the direction. Three from 120 degrees apart will make a spike..........

I would suggest to you from empirical observation from many years at sea that the direction matters enormously. As you say, three can create a spike. The danger is less that actual height of the waves than the shape of the wave form. the spike will have VERY steep sides and this is what kills ships.
For example waves in the North Atlantic can be quite high but the distance between the waves is relatively long, thus the slope is not too steep. Definitely a problem for a very long ship, but nowhere near the same problem as waves in the North Sea - They can be very steep and very dangerous.

[wholybee]

An interesting video. I first saw this years ago, but just stumbled into it again. Of note, if waves are traveling the same direction, as they add, they will begin to break before they can form "freak" waves. They found that waves at about 135 degrees apart can do it. And, they reproduce it in a wave pool. Similar to what CaptainRivet describes, in a pool of small waves, a huge "spike" will form many times higher than anything else around it.

https://www.youtube.com/watch?v=0lEsNMh03LI

[GordMay]

Originally Posted by Nicholson58

In wave action two or more wave crests always combine to form a sum. It doesn’t matter the direction. Three from 120 degrees apart will make a spike. Similarly, a crest and a trough cancel. The phenomenon is called constructive and destructive interference. Waves that split around an object such as an island will both turn in towards one another and form an interference pattern. The same is true for EM waves. This results in picket fence reception on the AM band.

The principle of superposition of waves states that when two or more propagating waves, of the same type, are incident, on the same point, the resultant amplitude, at that point, is equal to the vector sum, of the amplitudes, of the individual waves

When two waves come close to one another, their effects add together. If the crests, or highest parts of the waves, line up perfectly, then the crest of the combined wave will be the sum of the heights of the two original crests. Likewise, if the lowest parts of the waves (the troughs) line up just right, then the combined trough will be the depth of the two original troughs combined. This is known as constructive interference, in which two waves (of the same wavelength) interact in such a way that they are aligned, leading to a new wave that is bigger than the original wave.

However, if two waves are not perfectly aligned, then when the crest of one wave comes along, it will be dragged down by the trough of the other wave. The resulting, combined wave will have crests that are shorter than the crests of either original wave, and troughs that are shallower than either of the incoming waves. This is known as destructive interference.

In fact, if the two waves (with the same amplitude) are shifted by exactly half a wavelength when they merge together, then the crest of one wave will match up perfectly with the trough of the other wave, and they will cancel each other out. The resulting combined wave will have no crests or troughs at all, and will instead just look like a flat line, or no wave at all!

[Don C L]

In practical terms it is more possible now to avoid or at least to prepare for wave issues. The NOAA broadcast includes wave data. Ordinarily I only pay attention to the forecast for the prevailing northwesterly swells and ignore the others because they are typically so low or long period that they don't affect much. But the other day I discovered the error of my ways and it was humbling. There was a west swell with a 7 second period and a south swell with a 7 second period forecasted. They both had a fairly short fetch so they hadn't grown much, maybe only 5 ft or 2m, but the interference created a field of unpredictable waves at 90 degrees to each other. Some waves would just rise to a pyramid and kind of explode and there were areas of flat water to match. With winds up to 30 knots at times the tops would get blown off and we'd get a bit of moisture if we were in the way. Added to this the waves were bending coming around the local island so that added complication to the wave angles. It wasn't too comfortable. (But I did set a speed record for my boat!) In any event I will be paying much closer attention to the wave period and angle forecasts!

[Nicholson58]

Traveling between islands in the Eastern Caribbean the winds are 99% east. Wind driven waves are East. These pile up and curve around the north and south ends of the islands. Several of the islands are very tall, over 3000 feet and abrupt. This channels the winds so that the wind speed is sometimes 150 to 200 % increased and also curves around the islands. It is not uncommon to be sailing in15-20 apparent with 6-10 foot seas between islands. Conditions in the final five miles might then increase to 20-30 wind and 10-15 seas. Period on the waves is typically 8-12 seconds on the beam. If there happens to be a north swell as well then waves become crazy with the interference pattern added in. South bound may be OK but north is very rough. Fortunately there are some good predictions available so we plan transits for the easiest ride. Having a long heavy boat helps.

[MicHughV]

I didn't think this thread was still alive, but some years ago I got treated to a computer visual of that portion of water north of Denmark and south of Norway/Sweden.

I was further told that putting this particular model together took over a year to put together, as data was being added to the model from many different stations, locations, buoys, ship reports, etc, and also the known sea bottom, depths, underwater valleys, mounds, and what not.

The guy doing the modeling was a Ph.D who did this and little else.

Nonetheless, after all the myriad of data points were entered, various and sundry weather patterns were also inputted.

All in all, a very impressive effort and once the model was put into motion, one needed 10 pairs of eyes to follow it all..

It was interesting to note, when, from where and how " roque" waves, ("rogue" in this case being defined as unusually large waves in comparison to surrounding sea state), were formed and what their affect would be on surrounding land masses, ships at sea, etc. It's a complicated jigsaw puzzle that can change from day to day. From my point of view, predicting "rogue" waves seems to be part black magic, part common sense and part throw of the dice.

One can also think of...and see....the 100' waves that are formed off the coast of Nazare, Portugal, where the underwater terrain is mostly responsible for those.

Nonetheless, I think most anyone can agree that "rogue" waves do indeed occur.
I think the problem being that the word "rogue" is perhaps not the correct word to define this particular sea state, but I can't think of an appropriate word substitute.

[solzephyr]

Sailing our Beneteau 523 today, back to Marco, FL from LuLu Key the seas were confused. Every 7th swell felt like a rouge on the port beam.
Rock & Roll

zeph

[GordMay]

Originally Posted by MicHughV

...
I think the problem being that the word "rogue" is perhaps not the correct word to define this particular sea state, but I can't think of an appropriate word substitute.

According to NOAA*, “Rogues, [are] called 'extreme storm waves' by scientists, ...”
* “What is a rogue wave?”
➥ https://oceanservice.noaa.gov/facts/roguewaves.html

Referring to the famous 25.6m high North Sea “Draupner” gas platform wave [1995]. Jean-Raymond Bidlot [ECMWF], et al, used the terms “Freak Wave”, and “rogue wave”, interchangeably.
“What conditions led to the Draupner freak wave?”
➥ https://www.ecmwf.int/en/newsletter/...ner-freak-wave

[wholybee]

Originally Posted by MicHughV

...
I think the problem being that the word "rogue" is perhaps not the correct word to define this particular sea state, but I can't think of an appropriate word substitute.

Compounding this sailors have described rogue waves for many years (centuries?) and only recently have scientists confirmed they exist, and started to create a formal definition. The definitions scientists use, might not be appropriate for what sailors have been describing.

Example, if a scientific description says that waves higher than 2x SWH, or that they can occur every x number of waves, those definitions IMHO don't really agree with what sailors historically mean when they describe a rogue wave. Something like the Draupner wave is entirely different from that.