Is the seventh wave bigger?

Nostrodamus

Nostrodamus

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When I was a kid walking along the beach I was told that every seventh wave is bigger than the rest. Certainly stood there and counting them it seemed to be true. Even now when sailing there seems to be a pattern where every so often one wave is bigger than the rest.

In later life I read this was a total fallacy.

In some bad entrances where fishermen are trying to get out you can see them hovering near the entrance apparently waiting for a bigger wave to come past before rushing out.

So, for once and for all... is the seventh wave thing a fallacy or not?

All replies to the tooth fairy please
 
dear Tooth Fairy. You need to know about Rayleigh distribution.

For instance, if the 'normal' height of the waves is 1 metre, then

1 in 10 will be bigger than 1.07 metre
1 in 100 will be bigger than 1.51 metre
1 in 1000 will be bigger than 1.86 metre

Now I am not going to tell you what 'normal' is, nor which of the 1000 waves you are watching will be nearly twice as big as the normal ones.
 
When I used to go surfing, we used to sit out the back waiting for the bigger waves. They tended to come in sets of 3 or so. So you get a period of the "norm" and then 3 consecutive waves which were substantially bigger than than the rest. This would be generally but not always the case and would tend to be more true of waves generated by lange range swell.
 
sarabande said:
dear Tooth Fairy. You need to know about Rayleigh distribution.

For instance, if the 'normal' height of the waves is 1 metre, then

1 in 10 will be bigger than 1.07 metre
1 in 100 will be bigger than 1.51 metre
1 in 1000 will be bigger than 1.86 metre

Now I am not going to tell you what 'normal' is, nor which of the 1000 waves you are watching will be nearly twice as big as the normal ones.
Click to expand...

I thought Schodinder was the man for it now

http://sciencewise.anu.edu.au/articles/Monsters_of_the_Deep
 
From memory of my oceanography classes the7th wave theory is not accurate but is often close. There is a complex mathematical it is rarely practical. The reality is there are bigger waves in any sequence and they can be quite a lot bigger. In some areas this can be influenced by the shape of the shoreline which adds a few interesting harmonics to an already complex equation
 
sarabande said:
dear Tooth Fairy. You need to know about Rayleigh distribution.

For instance, if the 'normal' height of the waves is 1 metre, then

1 in 10 will be bigger than 1.07 metre
1 in 100 will be bigger than 1.51 metre
1 in 1000 will be bigger than 1.86 metre

Now I am not going to tell you what 'normal' is, nor which of the 1000 waves you are watching will be nearly twice as big as the normal ones.
Click to expand...
In open sea and theory that would be right, but we can all see much more variation than the above law. I presume that is because of interference patterns with reflections from shore, bending of waves around headlands and bays so the waves meet each other, different sets of swell meeting and obviously wind waves meeting the results of all the above.

With different heights and frequencies then every nth wave will be the height of all the different wave patterns added to together, then the next wave slightly smaller, the next wave a lot smaller (as more of of the wave patterns peaks drop towards troughs and so
on).

The calculations not so simple as I wonder how you could model even 3 wave patterns all interacting from different angles, frequencies and heights but we observe the effect every day.
 
As I understand it the water does not actually move, it is the energy within the seas that is being transferred. What amaze me is the speed of some of these waves as they travel.
I know when they are behind me the boat certainly can go much faster and going into them can slow me down a lot.
Even in deep seas off the Atlantic coast where there is no headlands there is defiantly some kind of pattern and for some reason some waves are far bigger than others. I don't know why though.
 
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sarabande said:
dear Tooth Fairy. You need to know about Rayleigh distribution.

For instance, if the 'normal' height of the waves is 1 metre, then

1 in 10 will be bigger than 1.07 metre
1 in 100 will be bigger than 1.51 metre
1 in 1000 will be bigger than 1.86 metre

Now I am not going to tell you what 'normal' is, nor which of the 1000 waves you are watching will be nearly twice as big as the normal ones.
Click to expand...

Does it not depend on the value of alpha?
 
When bodyboarding you count the waves, they normally come in sets of six, if there is a seventh then it is normally much bigger than the previous ones, never a good sight if you tried to catch the sixth one and failed to ride it in leaving you well out of position to ride the swell over the seventh and instead in the breaking zone....so I think this theory is true.
 
RupertW said:
In open sea and theory that would be right, but we can all see much more variation than the above law. I presume that is because of interference patterns with reflections from shore, bending of waves around headlands and bays so the waves meet each other, different sets of swell meeting and obviously wind waves meeting the results of all the above.
Click to expand...

Often called a "confused sea". Given the complexity of the mathematics that seems understandable!

Mike.
 
Waves undoubtedly come in sets of larger waves and flatter areas. The same happens with steepness, etc hence holes.

The longer you wait the more likely you are to find excessively big waves (100 year storm) or small waves.

On a shorter time scale I would agree these sets are noticeable weather its 5 or 20 I would not like to say it depends upon how much bigger you are looking for...
 
Nostrodamus said:
As I understand it the water does not actually move, it is the energy within the seas that is being transferred. What amaze me is the speed of some of these waves as they travel.
I know when they are behind me the boat certainly can go much faster and going into them can slow me down a lot.
Even in deep seas off the Atlantic coast where there is no headlands there is defiantly some kind of pattern and for some reason some waves are far bigger than others. I don't know why though.
Click to expand...

Oh that water does move, if you have ever been picked up by a wave you know it moves. Individual particles of water move in a circular motion within a circle which contains the wave length so you will see the wave motion well below the surface, I have observed a 50ft vertical motion at 300 feet for example, as we waited for an atlantic storm to blow itself out.
 
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Yes it it usually every seventh wave. If you are ocean sailing you see some enormous waves much bigger than the seventh on the horizon. Needless to say we would be on somebody else's horizon and they ar very noticeable when they come through.
 
Rogue waves - they do exist!

When I used to land mobos on their trailers on a beach slip in Oman there was a definite pattern but it changed every time due to the direction of the waves, state of the tide, etc. The trick was to have the patience to sit and work out the pattern and choose your moment wisely. In a large/marginal sea there was no second chance and the boats ended up beached on occasion.

There have always been stories of huge waves coming out of nowhere, not every 7th though. This was never scientifically observed until 1st Jan 1995 when the Draupner wave occurred: http://en.wikipedia.org/wiki/Draupner_wave
 
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