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What is this thing ?

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Øyvind
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What is this thing ?

Postby Øyvind » Wed Dec 12, 2018 11:00 am

Sometimes I see something that moves quickly through the water.
Not sure what this is, caught some footage of it, in this video:
https://youtu.be/2JCMn7tG41Y

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Re: What is this thing ?

Postby evan » Wed Dec 12, 2018 11:14 am

Just a wingtip vortex, a form of drag caused by the difference in pressure on the top and bottom of your wing that makes the water/air turning into a vortex propagating from the wintip. Just made visable by some sucked in air that stays trapped inside the vortex as long as it is strong enough (jus like the vortex when you drain your sink).
https://www.youtube.com/results?search_ ... tip+vortex






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Re: What is this thing ?

Postby ronnie » Wed Dec 12, 2018 12:51 pm

Another way to look at it.

The air at the surface of the water is actually under a high pressure, of 14.7 lbs/ sq inch. The surface of the water is at that same high pressure.

The centre of the vortex is at lower pressure than the water around it, because the water is spinning and being thrown away from the centre of the vortex. If the pressure in the water at the centre of the vortex is below 14.7 lbs/sq inch, the pressure of the air at the water's surface will force it into the lower pressure area. The wingtip breaching the surface is like a valve opening.

These wave vortices would be felt by a foil, as they are low pressure areas.



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Re: What is this thing ?

Postby ap888 » Wed Dec 12, 2018 6:11 pm

That vid is super kew ^^

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Re: What is this thing ?

Postby jumptheshark » Wed Dec 12, 2018 7:39 pm


TomW
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Re: What is this thing ?

Postby TomW » Thu Dec 13, 2018 3:34 pm

Those vortex streaks are going in opposite direction to his wing and or not anywhere near his wing. It appears to be some other small and Fast fish.

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jumptheshark
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Re: What is this thing ?

Postby jumptheshark » Thu Dec 13, 2018 4:03 pm

That short video clip shows it pretty perfectly with respect to kite hydrofoils.

The vortex is not visible until it has air in it. The foiler breaches a wing and you can clearly see the air propagate back from that spot through the vortex as it is sucked in by the negative pressure within. It traces back along a slightly wide path compared to the path of the wing as its rotating and spreading much like a wake from a boat.

It's pretty impressive, and it aint fish!
Last edited by jumptheshark on Thu Dec 13, 2018 4:24 pm, edited 1 time in total.

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Re: What is this thing ?

Postby ronnie » Thu Dec 13, 2018 4:07 pm

TomW wrote:
Thu Dec 13, 2018 3:34 pm
Those vortex streaks are going in opposite direction to his wing and or not anywhere near his wing. It appears to be some other small and Fast fish.
I was just about to post what jumptheshark said.


Last edited by ronnie on Thu Dec 13, 2018 4:10 pm, edited 1 time in total.

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Re: What is this thing ?

Postby BWD » Thu Dec 13, 2018 4:09 pm

jumptheshark wrote:
Thu Dec 13, 2018 4:03 pm
That short video clip shows it pretty perfectly with respect to kite hydrofoils.

The vortex is not visible until it has air in it. The foiler breaches a wing and you can clearly see the air propagate back through the vortex as it is sucked in by the negative pressure within.

It's pretty impressive, and it aint fish!
:thumb:

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Re: What is this thing ?

Postby TomW » Fri Dec 14, 2018 4:33 pm

The vortex is shooting backwards!? Wow


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