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Old 25-01-2019, 07:28   #1
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Freak waves created

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Old 25-01-2019, 09:08   #2
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Re: Freak waves created

Interesting!
"... What they discovered was that that they could recreate the wave using two smaller wave groups that crossed at a specific angle – approximately 120 degrees ..."
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Old 25-01-2019, 09:31   #3
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Re: Freak waves created

That's very interesting. It looks like the only thing one can do is have a boat with enough righting to handle a severe knockdown. Thankfully it's rare.
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Old 25-01-2019, 09:48   #4
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pirate Re: Freak waves created

Not that rare really.. I have known 90* cross sea's create a wave double the average on a few occasions if they meet just right.. just a matter of wrong place, wrong time.
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Old 25-01-2019, 10:01   #5
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Re: Freak waves created

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Originally Posted by boatman61 View Post
Not that rare really.. I have known 90* cross sea's create a wave double the average on a few occasions if they meet just right.. just a matter of wrong place, wrong time.
Hi Boatie,
What the video of the tank test shows is not a mere doubling of a wave momentum and height but something far larger.

This they say can only be recreated with conjoining wave forms arround 120°.

That is quite specific and very useful to know.
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Old 25-01-2019, 10:07   #6
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Re: Freak waves created

Yes, interesting. From the piece and vid it appears the rogue wave is a fairly specific event that occurs at the convergence of these two 120-degree wave fronts. Or am I misinterpreting this?
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Old 25-01-2019, 10:54   #7
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Re: Freak waves created

Interesting. However, I experienced a freak wave in the late 1970's with no cross seas visible at all. We had had a strong blow of 45 steady, gusting to 55 kts the night before, and by morning it had moderated to about 25 kts, with the steep, short wavelength sea that is kicked up during a blow. All waves were running the same direction, no cross seas at all. Typical waves were 10-12 feet. The freak was shaped like a breaker coming in to a beach with a very steep face. We first sighted it when it was miles away (visibility was excellent). I'd estimate the height at 40-45 feet. When it reached us the face had gone concave and it broke very shortly before hitting us. By observation, we were able to observe it for several minutes, so it was not just a pop up and fall phenomenon but had some stability.
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Old 25-01-2019, 11:02   #8
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Re: Freak waves created

The errant cross sea pattern really seems to be where the trouble lies. Best to be a little extra alert when in those conditions.

Dead men tell no tales, so who knows how many missing sailors have come across something like that? Not many obviously, but Joshua Slocum disappeared...
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Old 25-01-2019, 11:04   #9
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pirate Re: Freak waves created

Quote:
Originally Posted by Pelagic View Post
Hi Boatie,
What the video of the tank test shows is not a mere doubling of a wave momentum and height but something far larger.

This they say can only be recreated with conjoining wave forms arround 120°.

That is quite specific and very useful to know.
Not calling my example 'Rogues'.. just saying that the larger than average waves are not that uncommon and could be taken as rogues by some.
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Old 25-01-2019, 11:41   #10
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Re: Freak waves created

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Originally Posted by boatman61 View Post
Not calling my example 'Rogues'.. just saying that the larger than average waves are not that uncommon and could be taken as rogues by some.
Yup. I think a lot of what people call “rogue waves” are just part of the expected range in any typical seascape. Most wave forecasts use a model similar to NOAA’s Significant Wave Height:

Quote:
Significant wave height is an average measurement of the largest 33% of waves. We measure it because in many applications of wave data, larger waves are more "significant" (important) than smaller waves. For example, the larger waves in a storm cause the most erosion on a beach.

On average, about 15% of waves will equal or exceed the significant wave height. The highest 10% of waves could be 25-30% higher than the significant wave height. And on occasion (about one per hour) one can expect to see a wave nearly twice the significant wave height.
So a wave that is double the predicted (significant) wave height, and therefore many times larger than most of the waves, is actually pretty normal.
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Old 25-01-2019, 11:55   #11
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Re: Freak waves created

Since the '98 Sydney to Hobart race, with loss of lives, the weather forecasts here all say, "Please be aware, wind gusts may be up to 40% stronger, and wave heights up to 30% greater than the averages given here." Interesting to me, though, that the insurance adjusters down here do understand about there being lots larger waves as part of a normal wave pattern.

Interesting, the creation of the rogue wave, really shows how to anticipate what may happen in cross seas. It was cross seas in which we had the knockdown that broke our windvane rudder.

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Old 26-01-2019, 03:09   #12
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Re: Freak waves created

The problem in small boats is that its very hard to accurately measure wave height with all the pitching and rolling.

The cross seas and I think some upwellings are really what makes a Rogue wave.

They are common in the Gulf of Tehuantepec and I have seen some really strange and large sea formations quite far out

https://en.m.wikipedia.org/wiki/Gulf_of_Tehuantepec
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Old 26-01-2019, 03:39   #13
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Re: Freak waves created

All fits with my experience....

Only time I have had a nasty sea with a steady wave train has involved shallow(er) water.

The real rubbish has always involved a swell from one direction and a sea from another... typically SW swell and WNW/NW wind ( southern hemisphere ) .

That is the killer as boats approach Cabo de Hornos from the west... prevailing NWly gale over the SW swell.... combine that with getting to close to the relatively shallow waters near Diego Rameriz ... and its party time...
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Old 26-01-2019, 04:52   #14
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Re: Freak waves created

This an excellent Documentary with a well thought out and mathematically proven thereom on rogue waves, well worth a watch. Includes satellite pics showing the formation and travel of rogue waves.


Wave behaviour in reality can be explained by the Schrödinger equation.









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