Rogue waves

[Roberto]

almost 30m... satellite pictures taken from <A target="_blank" HREF=http://www.esa.int/esaCP/SEMOKQL26WD_index_0.html>esa site</A>

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by Roberto on 23/07/2004 09:46 (server time).</FONT></P>

 

[ubuysa]

A near 30 metre wave?????? Bloomin' heck /forums/images/icons/shocked.gif

Tony C.

<hr width=100% size=1>There are 10 kinds of people, those who understand binary and those who don't.

 

[dralex]

After the post yesterday about boat speeds, imagine how fast you could go down that one. I'm sure you could beat 19kn Robin- admittedly it may well be vertically with a lot of help from gravity!

<hr width=100% size=1>Life's too short- do it now./forums/images/icons/wink.gif

 

[Sunnyseeker]

The e-mails must be doin the rounds I just got sent this link about the huge waves by a friend who doesn't want to do any ocean sailing now!
http://news.bbc.co.uk/1/hi/sci/tech/3917539.stm

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[dralex]

Would a sea acnhor or drogue work for a wave of this amplitude? I am not sure of the maximum wave dimensions these devices will work at. Theoretically the wavelength is not an issue as long as you have enough rope. I'm sitting here trying to imagine how big that wave would look and also how scary.

<hr width=100% size=1>Life's too short- do it now./forums/images/icons/wink.gif

 

[Cobra]

"Would a sea acnhor or drogue work for a wave of this amplitude?" I think that maybe a parachute would be a bit more appropriate!

<hr width=100% size=1>When God invented time he didn't give me enough of it. ND!

 

[Chris_Rayner]

Re: Wave length

Surely the wave length vs.height is critical here. Anyone who has sailed around the Iles Chausey will have experienced waves of this height; thing is, they're tides with huge wavelength and low frequency. I guess if the wavelength of this wave were very long you'd barely notice it, so height isn't everything. The things I'd most like to know are the angle of the wave front to the horizontal, and whether it's breaking or not. Anything much above 30 to 40 degrees would be pretty sphincter tightening, top it off with a breaking crest and I suppose it'd be goodnight Vienna!

Chris

PS Ooops, tides not this height, confusing metres and feet. Nevertheless, general point holds.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by Chris_Rayner on 23/07/2004 11:22 (server time).</FONT></P>

 

[dralex]

Re: Wave length

I'd guess that if it was a 30m SWELL it would be called a swell, not a wave-that didn't dawn on me before.

<hr width=100% size=1>Life's too short- do it now./forums/images/icons/wink.gif

 

[StugeronSteve]

No. I think a prayer book would be more effective! /forums/images/icons/smile.gif

<hr width=100% size=1>Think I might draw some little rabbits on my head, from a distance they might be mistaken for hairs.

 

[StugeronSteve]

Re: Wave length

If I am reading the horizontal scale correctly the crest to trough distance would seem to be in the order of 150m.

<hr width=100% size=1>Think I might draw some little rabbits on my head, from a distance they might be mistaken for hairs.

 

[ROCKETSHIP_11]

THIS IS A LINK TO "JAWS" SURF BREAK IN MAUI CHECK OUT THE VIDEOS OF VERY BRAVE GUYS RIDING 50 FOOT WAVES, THE WAVES ARE MOVING SO FAST THE SURFERS HAVE TO BE TOWED INTO THE WAVE BY JETSKI,
http://www.maui.net/~hookipa/jaws/

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[Roberto]

Re: Wave length

one of the documents in the site states: "these waves are generally 50% steeper than the significant steepness"; even if the significant steepness of a rough sea is less than the steepness of its scattered breaking waves, the impression of a 50% steeper 30m wave must really be something..



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[dralex]

I've seen footage of Jaws before- I'm surpried these guys can surf because their balls must be massive. Alternatively they've had the optional lobotomy. I get scared attempting to surf 1.5m waves!

<hr width=100% size=1>Life's too short- do it now./forums/images/icons/wink.gif

 

[Chris_Rayner]

Steepness

Not sure how you measure that. Do they mean angle to horizontal or gradient, and what's 50%? If the faces of most of the waves are say, 20deg to horizontal then is 50% extra 30deg.? On the other hand 150% of 30deg might be much more exciting. Once you get up to 150% of 50deg then it's ver' steep.

Chris

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[Roberto]

Re: Steepness

Steepness is the ratio wave height/wave length; from what I understand in the article a 50% increase would mean that in a significant steepness of 1:15 a rogue wave should be 1:10 steep

To relate steepness to angle of water surface slope I suppose one should make several assumptions about wave shape, and at which points of the wave the angle should be measured (perhaps the tangent to crest ?)



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[TheBoatman]

Re: Steepness

Anyone that watched the TV prog about these waves would know that even a boat (ship) the size of the QE2 ain't big enough.
If it can cause a problem to 50.000 tons with 60,000 Hp driving it somehow I don't think my 20 Hp and 32 feet is going to crack it. I think faced with a wave of that magnitude I would simply bend down and kiss my arse good bye!

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[Roberto]

Re: Steepness

otoh (a lot of spare time for conjecturing today), as a steepness >1:7 causes deep sea waves to break, in a sea with a significant wave steepness >1:10.5 a rogue wave would immediately break

back to work then -.<)





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[ongolo]

Re: Steepness

I think they measure a wave of say 100m length with a 50% height =50m in this case.

So a 300 long wave with 10% would then be 30m.

We once measured gradients and it always looks much steeper than it really is.

I think when a vertical wall of water 30m high crashes on a yacht, dont worry about sinking, you have your skull broken instantly. I think.

regards ongolo


<hr width=100% size=1>So what......... it floats

 

[Sybarite]

This programme explained that a rogue wave apparently draws energy from the waves around it which consequently are smaller than average. However before the rogue wave there is a rogue hollow into which a ship can plunge leaving it exposed to the abnormal breaking wave.

Ships' standard design was based on waves of 15m maximum which have a striking force of 15 tons/m². A 30m wave has a striking force of 100 tons/m².

Time to keep the head down.

John

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[pampas]

In 1976 I was on a 250,000 ton tanker and experienced a large wave off South Africa sweeping down the flush deck, bending two breakwaters (Each about nine feet high) and damage to other equipment, height unknown, I did not see it as I was in the E/R, but from all accounts it came from nowhere, speed at the time was about 12knots as we were on stand by for bad weather. I personally think that what we hit was the begining of one of these rouge waves. A Ben boat about two years before hit a wave in the same place and from No2 hatch forward bent the hull down by about 15 degrees, lucky not to have broken in two. Limped into Cape Town a sorry site. Thats why I limit my sailing to Falmouth Bay.

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