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
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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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.
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.