What, really, is a rogue wave?

[CassidyNZ]

Originally Posted by newhaul

Put it simple here a 20 ft swell on a 15 second period is gentle but put the same swell on a wind driven 5 second period . The sides are steep enough to roll a vessel or pitch pole them as well .

There is an example in an old Sydney Hobart race where almost half the field was severely damaged due to steep non breaking was . ( Don't recall exactly what year)

Mmmmmm . . . . .

[Don C L]

Yeah for example, if you are broad reaching in a steep set of waves and there is a strong breeze to boot, as the wave catches up to you the boat suddenly doesn't have much water under it and will heel to fall over on the face of the wave and the wind will encourage that, and a broach will be in the works.
I believe, but I cannot recall the article that mentions it, that a wave that is double the height of the average is still not yet in "rogue" category.

[Alan Mighty]

Originally Posted by river251

Is this a fair assumption? A rogue wave is not defined by a certain height, but by how different it is from other waves the boat is sailing through.

Yes. Rogue waves are defined as those with height equal to or greater than twice the significant wave height. Same goes for rogue holes.

[GordMay]

Originally Posted by Alan Mighty

Yes. Rogue waves are defined as those with height equal to or greater than twice the significant wave height. Same goes for rogue holes.

Indeed.
A rogue wave is usually defined as a wave that is twice the significant wave height of the area, at a given time.
According to NOAA:
Rogues, called 'extreme storm waves' by scientists, are those waves which are greater than twice the size of surrounding waves, are very unpredictable, and often come unexpectedly from directions other than prevailing wind and waves.

[Benz]

Any wave that sloshes water on my deck is a rogue wave to me.

[LittleWing77]

Originally Posted by er9

i wonder if its possible to collapse a wave at its base using sound or vibration frequencies? we could tow several long warps that vibrate behind the boat and collapse oncoming waves.

Or, like they did with that embassy years ago, play rock music really, really loud!

LittleWing77

[LakeSuperior]

Originally Posted by er9

i wonder if its possible to collapse a wave at its base using sound or vibration frequencies? we could tow several long warps that vibrate behind the boat and collapse oncoming waves.

The answer is a resounding yes! However, it is totally impractical for this application. The actuator and the required energy to collapse a wave make it a non-starter.

Active noise control is the realization of this concept. Active noise control, popularly used in headphones, was also used by Lotus cars and a number of aircraft manufacturers to reduce weight by reducing the amount sound absorbing materials.

[sowwaninii]

Susan Casey
The Wave: In Pursuit of the Rogues, Freaks, and Giants of the Ocean
A recommended read on rogue waves and big wave surfing. Very interesting!!

[hzcruiser]

Originally Posted by er9

i wonder if its possible to collapse a wave at its base using sound or vibration frequencies? we could tow several long warps that vibrate behind the boat and collapse oncoming waves.

A wave is not hollow until it breaks, so there is nothing really to collapse. As it's roughly triangular you might compare it with a pyramid, which appears to be very stable and long lasting. They don't collapse that easily.


To reduce the strength of the wave, you'd have to somehow push several tons of water to the side within a few seconds.

[newhaul]

Originally Posted by hzcruiser

A wave is not hollow until it breaks, so there is nothing really to collapse. As it's roughly triangular you might compare it with a pyramid, which appears to be very stable and long lasting. They don't collapse that easily.


To reduce the strength of the wave, you'd have to somehow push several tons of water to the side within a few seconds.

US Navy battleship . Look at her slide sideways.

[Wallaby]

Originally Posted by CassidyNZ

No “wave”, rogue or otherwise, is of any danger to a sailing boat until it breaks. It is said that a tsunami that kills a million people ashore will pass under a sailing boat at sea completely unnoticed.

To be honest, I still do not know if I was hit by a rogue wave or a whale. On an overnight offshore trip, around 3am, with waves about 3-5 feet, and winds of 10+/- knots on the beam, I was broadsided and 'knocked down' with a massive 'bang' and a very large amount of water over the windward side of the boat (so not a gust). Luckily, I was laying on the leeward seat, and harnessed in. The boat heeled so much I could not get up without falling over the side. The impact dislodged the wind generator and shook the back-stay so much the ssb antenna connection came free. Down below was a mess.

The next few minutes were a panic--checking for anything behind, damage to my vessel etc. There was nothing found, with no damage underneath, as seen later that day, and upon haul-out.
Assuming it was a rogue waves, imho, they are dangerous!

[Don C L]

Well that does it. I am adding storm oil and Enya to my sea calming kit!

[Cadence]

Originally Posted by DDabs

nothing scarier than the sound of a breaking wave behind you... my shoulders raise upwards at just the thought

Following seas suck!

[chasfgr]

usually experienced when two wave trains meet in shallowing water.
Very noticeable around the 100m line in Biscay after some brisk weather.
They are breakers about 50% higher than the swell in which they're running and usually assault one at night (well, you can see them coming in daylight).
They'll often shove your masthead (in a small boat) into the sea, and you as well if you're not strapped in, if hit abeam.

[thinwater]

Originally Posted by tkeithlu

Agreed, Cassidy, but you may be combining two different phenomena. A tsunami at sea is only inches or a few feet tall, and spread over a lot of area. It has a bunch of energy in it. When it hits shallow water, all that energy goes into wave height. Rogue waves on the other hand are made of two wave patterns that intersect additively....

Actually, you are still off the point in your understanding of tsunamis. They are not related to the rouge wave discussion. They are a separate catagory.

The defining characteristic of a tsunami is very long wave length, and as a result of that, very high speed. They are caused when miles of seabed move vertically. Wind-generated waves usually have period (time between two successional waves) of five to twenty seconds and a wavelength (distance between two successional waves) of about 300 to 600 ft. (100 to 200 meters). A tsunami can have a period in the range of ten minutes to two hours and a wavelength in excess of 300 miles/hr (500 km/hr).

Finally, rouge waves can be momentarily very steep without breaking. This is a result of addition, and thus can result in great steepness without breaking. It is common to have waves reach twice the average height, particularly in a storm with varying period waves. These are not rouge waves, this is normal variability, though the line between the two is blurry.

I don't think this is fear mongering. The required conditions are quite rare, and complacency is bad.