NY Times Article on Rogue Waves

[ssullivan]

http://www.nytimes.com/2006/07/11/sc...cFmT1MPPDPh+ag

This is a NY Times article on Rogue Waves that might be of interest to forum members.

[Sandero]

The deal with big waves if when they are short.. or the wrong length for your vessel and of course when they break. I have sailed through/over enormous "waves" or swells... don't know the term but it was like sailing over rolling hills of 50 - 100' high. These monsters were obviously from some very nasty weather thousands (perhaps) miles away and by the time they arrived where we were they were no threat at all and it was just amazing to sail through the lovely long hills.

On the other hand breaking 15 - 20 foot waves are terrifying if you are in small yacht when you consider that a square meter of water weighs a ton... and imagine tons and tons of water crashing on your deck at once! OUCH.

Remember in Perfect Storm the wave that did them in at the end? It broke over them and buried that trawler. You don't want to be around those fellas.

Jef
sv Shiva
Contest 36s

[ssullivan]

Jef's right. It's *breaking* waves that are the main concern. With enormous waves in swell form, it would seem larger ships would have more problems than little old sailboats like most of us have. We could ride up and over. They have to break through.

[Alan Wheeler]

OK, I can bring in some of my understand in wave theory here with sound. Sound waves are kinda different but the same. The difference with water is it has mass and fluid motoin. But the transference of energy is similar.
The "freak" wave and "rogue" wave are two very different beasts. A rogue wave is created by the collapse of two or waves in close proximity to one another. The colapse maybe due to several differing factors. But the energy itse;f is still there. You can't just turn off energy, it has to be changed to something else. There is nothing else there apart from more water, so the energy is "pumped" back into producing a wave. However, this "new" wave is created by the energy from the collpase of the other waves and not by the wind and transfer of existing energy through the fluid. So the "new wave" can travel in a different direction to the surrounding waves. The direction is a sum of how the energy was imparted to this new wave of water. Due to several other factors, the energy traveling at a different direction to wind, tide and the fact that some of the original "collapsing" energy is also being imparted in a verticle direction, these Rogue waves stand very high and very steep. However, becuase of this characteristic, they also can not support themselves for very long. So they will collapse again, soon after they were formed. So we don't have giant 100ft waves craching onto shore lines.

A freak wave is a slightly different animal. It is often a wave in a series of wave cycles. They travel in the same direction as the rest of the wave energy and can travel tremendouse distances. They are created via very different factors. They are often the huge roller coaster type monsters. Not saying they aren't dangerouse. They can be so big they will still roll or pitchpole a vessel in the right circumstances.

[Intentional Drifter]

Interesting stuff. Always nice to go to the primary sources instead of the reporter's interpretation of the primary source, too.

MaxWave's project website is: http://w3g.gkss.de/projects/maxwave/
They have links to various reports, descriptions and analyses of their data. Fascinating. One of the off-shoot projects involves the real time analysis of wave from various stations around the world. Surfers with a death-wish would love this: http://www.wamos.de/ (click on projects for the map of data stations.)

Fornberg's article can be accessed at: http://amath.colorado.edu/faculty/fo...reak_waves.pdf

I cannot even begin to get through Fornberg's math (sorry, my Ph.D. was in an entirely different field. Perhaps some of the engineers around here can help out.), but in the conclusions/appendix, he notes:

"...we note that amplitude, or wave height, is not necessarily the best measure of danger for a vessel at sea. Wave steepness is also important, since even a small vessel can ride over large, but long seas provided they are not too steep, a situation that often prevails in the Southern Ocean. Wave breaking is another important feature. In their review of model tests, actual capsizes, and mathematical, statistical and engineering analyses, Kirkman & McCurdy (1987) concluded that `As a rule, we believe, no non-breaking wave is dangerous' for offshore yachts...."

And:

"Details of the wave shape can also be important in assessing danger. For example the deep trough, or `hole in the sea', often reported preceding a freak wave, presents a special hazard, as explained by Mallory (1974). When a fast ship meets a freak wave head-on, she first steams downward into the trough, burying her bow. Now the forward part of a ship usually has great buoyancy. So the bow forcefully attempts to rise just as the giant wave breaks on deck aft of the ship's forward buoyant area. The resulting shear forces on the hull can cause significant structural damage, usually near the bulkhead between Nos. 1 and 2 hatches."

The Kirkman and McCurdy cite is from the classic CCA book:

Kirkman, K.L. & McCurdy, R. C. 1987 Avoiding capsize: research work. In Desirable and Undesirable Characteristics of Offshore Yachts (ed. J. Rousmaniere), pp. 57-74. Technical Committee of the Cruising Club of America, Nautical Quarterly Books, W. W. Norton.

ID

[sneuman]

OK, first of all it's well known that breaking waves are the real concern and I can add my voice to others who have experienced that phenomenon first-hand.

While I have not seen anything like the freakish 100ft+ behemouths described in this article (and hope to hell I never do), I have seen the "unexceptional" 30+ft ones mentioned.

Not knowing what your exact presentation will be to a following sea when/if it breaks is the real challenge and fear.

Over three days helming in really big stuff, I learned to get square with a breaking wave one or two lengths back - if it broke then, it would need to build energy/mass for a while before breaking again, which meant I had a good chance of avoiding the danger. The problem is what Allan suggests - the cumulative effect of two or more waves coming together and forming a third that is much more erratic. The direction of this secondary wave and when it decides to break is much less predictable. Also, when three waves come together at slightly different angles the result is a steep rising pyramid that doesn't exactly break as much as it crashes. Now that is a sight I will never forget!

[capt lar]

I have be up and over some rogues and I agree with comments suggesting that the breakers are the worst. I would add that when cruising close to shore, a very large wave can get huge and a roller can become a breaker if the bottom is coming up. We got caught once in this situation and my choice to power to it and get over (PDV) was correct. Those that could only watch it grow and start breaking really got pounded, as did everyone on the beach behind us.

Larry