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ventilation

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gerrob1
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ventilation

Postby gerrob1 » Wed Mar 11, 2020 11:16 am

There is a lot of talk about ventilation. What exactly is that maybe i am stupid so i need a simple explanation please.
Also howe do you realise when your mast is not stiff enaugh?

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Peter_Frank
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Re: ventilation

Postby Peter_Frank » Wed Mar 11, 2020 11:30 am

Ventilation is when the wing comes near or above the surface, and part of it or all of it gets "air".

Even if only part of it is exposed to air, wing might suddenly stall and lose all lift, because the air gets sucked into a bigger area of the wing, thus it does not lift anymore.

Ventilation was used most as a term when hydrofoil started, but now many are using the term "Breaching" instead, for the same.

Should not be confused with the term cavitation, as this is when the water starts to "boil" locally at parts of the wing at really high speeds, or low pressure.
Happening above the typical speed range kitefoilers ride, but it can happen at badly shaped/designed wing profiles also.

Regarding when your mast is not sufficiently stiff - well, only you can feel this, if not racing, it is a matter of how you feel.
Do you feel it is "sloppy" or not?
Might be impossible for you to know, if you have no other mast to compare to though :roll:
Using or borrowing another foil wont give you the answer, as you need ONLY to replace the mast, to feel the difference, when new to kitefoiling.

8) Peter
These users thanked the author Peter_Frank for the post (total 2):
knotwindy (Wed Mar 11, 2020 6:07 pm) • edt (Wed Mar 11, 2020 9:42 pm)
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gerrob1
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Re: ventilation

Postby gerrob1 » Wed Mar 11, 2020 11:58 am

ok thx for that. Is that the reason that when i go in fast speed upwind in sloppy sea. Its end up with a crasch forward and i feel it when it starts.

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Re: ventilation

Postby Peter_Frank » Wed Mar 11, 2020 12:14 pm

gerrob1 wrote:
Wed Mar 11, 2020 11:58 am
ok thx for that. Is that the reason that when i go in fast speed upwind in sloppy sea. Its end up with a crasch forward and i feel it when it starts.

Most likely yes, as when going fast upwind you are tilted/canted a lot, so one side of the wing might catch air between the chop waves, and you will crash forward indeed, often able to feel it coming as you say :naughty:

Longer mast, or more time on the water so you can avoid it by riding a tad deeper in these conditions.

Racers use 110-115 cm masts because of this.

But a 100 cm will do fine for most non-racers also, and a better compromise I would say.

I am doing fine on a 92 cm, but never riding fast upwind so does not count...

8) Peter

gerrob1
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Re: ventilation

Postby gerrob1 » Wed Mar 11, 2020 12:35 pm

thx a lot Peter for reply and explanation

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Re: ventilation

Postby revhed » Wed Mar 11, 2020 7:23 pm

No mention of "STRUT" suck as ventilation, kinda like fin "spin out" maybe?
I would think this is also ventilation? And quite possibly much more common than wings breaking surface.
I think twist, texture, profile can affect this.
Have a strong feeling pressure differences may play into as well.
Can indeed provoke on most KBHFs with aggressive tight turn most notably upwind.
Very different from wing breach.
Also remember well a D I Y KBHF with noticeable imperfection at STRUT to fuse joint causing this and was sure because just this isolated repair cured.
R H

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Re: ventilation

Postby slowboat » Wed Mar 11, 2020 9:18 pm

I don’t think there is a consensus on strut flex. Obviously if it is a noodle, that is bad but some reputable producers such as Armstrong claim they have some flex designed into their struts which h makes them more reactive. Kinda like flex in surfboard fins. I’m personally agnostic on the question.

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Re: ventilation

Postby edt » Wed Mar 11, 2020 9:44 pm

Image

hmmm air. some wings fall down if they get ventilated because air goes under the wing some can keep a grip but it never helps you

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Re: ventilation

Postby plummet » Thu Mar 12, 2020 5:59 am

To add to the above. I fast tomohawk crash forward is generally not ventilation of the front wing. Typically it is ventilation or complete breach of the rear stabaliser. The rear stab is providing the force that you are pushing against to keep the front wing in the water. Remove or significantly reduce that force and your front leaning bias will tomohawk you instantly into the water onto your face.

The fix is foil deeper in the water and follow the contour of the sea. The choppier and bigger the swell the deeper you need to go. There comes a point of roughness where you will have to consider a longer mast to get a reliable ride.

Typically front wing breach and ventilation leads to a rocky recoverable right.

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Re: ventilation

Postby dice » Thu Mar 12, 2020 8:06 am

Peter_Frank wrote:
Wed Mar 11, 2020 11:30 am
Should not be confused with the term cavitation, as this is when the water starts to "boil" locally at parts of the wing at really high speeds, or low pressure.
Happening above the typical speed range kitefoilers ride, but it can happen at badly shaped/designed wing profiles also.
Isn't cavitation a good thing? I once saw a myth busters episode about submarines being launched from above water I think and to reach the highest speeds they needed cavitation.
So if a wing gets cavitation, then this means it's not bad shaped in that case.


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