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Tip of Foil Breaching Surface

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Peter_Frank
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Re: Tip of Foil Breaching Surface

Postby Peter_Frank » Fri Sep 08, 2017 7:10 pm

You are probably right Mossy, and I like some keep track of the words :thumb:

Although I did not know the English word "Breaching" - it means "breaking" in the direct translate, and of course used when things like fish break the water surface and go above so makes sense.

But ventilation is still correct IMO, as if you go over the surface, and down "perfectly" like you can do in a jump, you can actually ride on without ventilation.

So what happens is, that a part of the wing is over the surface, maybe not even over, if just the topside of the wing is on the surface, air will be sucked down and ventilation can occur, and you will drop like a rock :roll:

I dont know of poor design being able to create ventilation...
But "cavitation" yes, if a poorly designed profile at high speeds, but that is cavitation because of locally very low pressure points so the water will boil.
Got nothing to do with ventilation, which is when air from the surface is sucked down to the wing and you will lose a lot or all lift :wink:

8) PF

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Re: Tip of Foil Breaching Surface

Postby Leelanau » Fri Sep 08, 2017 8:24 pm

Thanks for clarifying the terminology. My understanding is as you've defined it. The reason I was figuring it was just a tip breach which initiated the ventilation was that it happens when the board is heeled over (either carving or when driving up wind hard) and I'm pretty sure a significant portion of the wing is still buried in the water. My simple mind figures that with 90% of the wing in the water I should still have 90% lift. Instead it's 0%, and it happens abruptly. Ultimately, the point is moot - I just need to avoid doing it.

To davesails7's comment, it was actually that same video that got me thinking about this. In part, trying to distinguish marketing from fact.

Mossy 757
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Re: Tip of Foil Breaching Surface

Postby Mossy 757 » Fri Sep 08, 2017 8:25 pm

Peter_Frank wrote:
Fri Sep 08, 2017 7:10 pm
I dont know of poor design being able to create ventilation...
But "cavitation" yes, if a poorly designed profile at high speeds, but that is cavitation because of locally very low pressure points so the water will boil.
Got nothing to do with ventilation, which is when air from the surface is sucked down to the wing and you will lose a lot or all lift :wink:

8) PF
Gunnar mentioned in his foil review of the new Spotz Shark that the Banga foil ventilates the strut in certain circumstances, seemingly without warning, while going fast.

phpBB [video]


I also heard a buddy say the Sword RS ventilates the strut a bit during normal riding. So this has nothing to do with a lifting surface leaving the water, just in normal riding conditions sometimes the forces that the mast creates will suck air down and create problems.

So all said, there are really 3 issues:

1) Breaching - wings come out of water and air is less dense than water so you lose lift and crash
2) Ventilation - air gets sucked in along a lifting surface (maybe because you breached the wing tip, but sometimes it just happens on the strut)
3) Cavitation - the shape of the lifting surface creates too much of a negative pressure zone which causes the water to "boil" and create air pockets

All 3 cause crashes for the same reason - a hydrofoil cannot create sufficient lift to carry a rider when pushing against air instead of water. The physical principles behind these three phenomena are very different.

As a side note, some lifting surfaces under water create wingtip vortices which can induce ventilation as well, so it's not always the strut, if you were riding with the wings close enough to the surface of the water, they might ventilate through their vortices anyway (unless there are winglets designed to disrupt these vortices).

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Re: Tip of Foil Breaching Surface

Postby marekmk » Fri Sep 08, 2017 9:53 pm

]"The flatter the wing is at the tip, the less problem you have when it breaches. Riders who switched to the flat Sword wings noted this.
LF also notes this in their new Thruster video with thekiteboarder.com. The new Thruster is completely flat and they say you can ride around with large parts of the wing out of the water"[



from my experience with the ketos not true about foil being flat and not ventilating/breaching.
the easy wing is anything but flat and I can keep it skimming just on the surface of the water without the pressure underneath the wing collapsing and throwing me of.
also i can keep 20% of the wing at a steep angle out of the water without feeling that precarious


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