Standup Zone Forum

The Foil Zone => Foil SUP => Topic started by: Califoilia on June 28, 2019, 05:25:05 PM

Title: "Anatomy of a Breach"
Post by: Califoilia on June 28, 2019, 05:25:05 PM

Saw this on IG, and thought it was interesting how the breach of a tip that instantly pulls in so much air to disrupt the water flow over the wing, and down goes the foil, board, and rider almost immediately after...

https://www.instagram.com/p/BzEySSgnvfi/?utm_source=ig_web_button_share_sheet

Title: Re: "Anatomy of a Breach"
Post by: Admin on June 28, 2019, 05:30:02 PM

That is amazing footage. 

Title: Re: "Anatomy of a Breach"
Post by: PonoBill on June 28, 2019, 06:50:28 PM

Same thing happens to a paddle, though with a little less derama. I have lots of really boring underwater paddle shots showing tiny surface air trails that expand across the back of the paddle.

Title: Re: "Anatomy of a Breach"
Post by: SUPeter on June 29, 2019, 04:35:28 AM

Makes you wonder if one or a series of very thin, vertical , top mounted "fins" would inhibit the propagation of air being sucked into the negative pressure zone.

Title: Re: "Anatomy of a Breach"
Post by: Lazz on June 29, 2019, 04:48:50 AM

Some interesting footages, what can happens "down" there.

https://www.youtube.com/watch?v=DijdU0rmDdc (https://www.youtube.com/watch?v=DijdU0rmDdc)

https://www.youtube.com/watch?v=K_w3gcvA87I&t=1094s (https://www.youtube.com/watch?v=K_w3gcvA87I&t=1094s)

Title: Re: "Anatomy of a Breach"
Post by: Rider on June 29, 2019, 07:21:57 AM

Maybe use some micro vortex generators like I had on my Maule....

Title: Re: "Anatomy of a Breach"
Post by: Lazz on June 29, 2019, 07:52:18 AM

Quote from: Lazz on June 29, 2019, 04:48:50 AM

Some interesting footages, what can happens "down" there.

https://www.youtube.com/watch?v=DijdU0rmDdc (https://www.youtube.com/watch?v=DijdU0rmDdc)

https://www.youtube.com/watch?v=K_w3gcvA87I&t=1094s (https://www.youtube.com/watch?v=K_w3gcvA87I&t=1094s)

I wonder if the SUP-Foil designers also perform test in a hydrodynamic tank or only playing with their CFD software.

Title: Re: "Anatomy of a Breach"
Post by: surfcowboy on June 29, 2019, 08:59:44 PM

Sano, thanks for posting this. I saw it but couldn’t stop and post here.

It’s amazing to see that air run down the foil like that. SUPeter, you are on to something worth testing for sure.

Title: Re: "Anatomy of a Breach"
Post by: PonoBill on June 30, 2019, 08:01:30 AM

You need a lot more speed and power to worry about cavitation. It's air entraining that we need to prevent, in paddles, fins and foils, so SUPpeter is correct--ribs to break the air stream would help. The little reversed wings on Konihi and Mana paddles function similarly by breaking the cohesion of entrained air to the paddle blade, which prevents air on the face from finding a comfy home on the back of the blade, where it increases slip. Windsurfers talk about fins cavitating, but there's no way that happens at low windsurfing speed, it's just air getting under the board and making its way down the low pressure area of the fin.

Note the water speed in the water tunnel in the video--looks like something in the range of 50mph. Nice water tunnel--my paddle testing water tunnel reached a blistering speed of about 2mph for about 2 seconds.

Real cavitation is water turning to vapor both from the heat transferred to the water by friction and the vacuum created by the Bernoulli effect. Takes a lot more energy than wind or humans can generate even at the nucleate (not bulk) vaporization level, except perhaps in the fastest of the foil sailboats.

Title: Re: "Anatomy of a Breach"
Post by: Rider on June 30, 2019, 07:50:40 PM

Thanks for confirming my idea. If you have any more questions don’t hesitate to ask.... if  8)