Forums > Windsurfing Foiling

Awesome video by Andy Laufer, and a crash question. Overfoiling or no?

Reply
Created by aeroegnr > 9 months ago, 18 Jun 2021
boardsurfr
WA, 1603 posts
6 Dec 2021 11:43PM
Thumbs Up

Select to expand quote
Sandman1221 said..
Sorry, you are just making up an explanation without any data, and Nico never showed the problem stopped after sanding the mast! That foil is just not strong enough for the conditions, period.


Sorry, that's just bloody nonsense. My data are the angle of the board, very clear for anyone who experienced this. Even better data are Nico's screen shot. As Nico plainly states in the video, he has sailed the same foil in similar conditions many times, with the only difference being the mast. That's quite a controlled experiment. And he happens to be a top-level slalom and foil racer. I'll keep trusting his assessment of what happened, over the doubts of some random foilers who think they know better.

Sandman1221
1971 posts
7 Dec 2021 3:39AM
Thumbs Up

It does not sound reasonable to me that just because the mast was not sanded it sucks air down. I think there is something off with the design of the mast that allows it to flex under load. If the mast flexes under load, and the load is coming from the windward side, then cavitation would occur on the leeward side, which it does.

Grantmac
1414 posts
7 Dec 2021 4:42AM
Thumbs Up

I've actually held AFS and IQ foil setups, the AFS is very flexible in comparison. Even the regular Starboard setup is significantly stiffer.
The fuselage to mast connection has absolutely zero flex. The original non-plus fuselages were not as thick as the plus and there were a few that failed but none of that has been current for at least two model years.
There have also been cracks in one part of the starboard masts but those were again not current or IQ versions.

The masts have a smooth sticker that goes along part of the leading edge which makes the surface very smooth and that can absolutely cause boundary layer separation. In my mind as someone who has a casual background in aerodynamics that is absolutely what we are seeing here and there are simple experiments to test whether a change in surface would be beneficial such as running a line of 3M Blenderm tape along the leading edge.

Sandman1221
1971 posts
7 Dec 2021 6:08AM
Thumbs Up

Select to expand quote
Grantmac said..
I've actually held AFS and IQ foil setups, the AFS is very flexible in comparison. Even the regular Starboard setup is significantly stiffer.
The fuselage to mast connection has absolutely zero flex. The original non-plus fuselages were not as thick as the plus and there were a few that failed but none of that has been current for at least two model years.
There have also been cracks in one part of the starboard masts but those were again not current or IQ versions.

The masts have a smooth sticker that goes along part of the leading edge which makes the surface very smooth and that can absolutely cause boundary layer separation. In my mind as someone who has a casual background in aerodynamics that is absolutely what we are seeing here and there are simple experiments to test whether a change in surface would be beneficial such as running a line of 3M Blenderm tape along the leading edge.


Grantmac what AFS foil did you have? I have the W95, so I think third generation (hollow mast) with the newest version coming out a year or two ago (solid mast). I have a big smooth AFS sticker on my foil across the top on both sides and I never drop out of the air like Nico or more relevant aeroengr who is probably going a similar speed as I am. So I am not buying it right now that the mast smoothness or sticker are causing the cavitation. Maybe there is a production issue with some masts not being built to specification? Starboard had a delamination issue in the past with boards, so why not an issue with the carbon mast layup?

Grantmac
1414 posts
7 Dec 2021 10:17AM
Thumbs Up

You aren't pushing your foil like he is.

Paducah
1862 posts
7 Dec 2021 10:39AM
Thumbs Up




Select to expand quote
Grantmac said..
I've actually held AFS and IQ foil setups, the AFS is very flexible in comparison. Even the regular Starboard setup is significantly stiffer.



Yes and not really. In torsion, the orig 95 and AFS are very close but the IQ is much stiffer. In flex (side to side), the AFS is significantly stiffer than the orig or IQ.

windfoilfan.glissattitude.com/devices/foil/chart/tors_module

windfoilfan.glissattitude.com/devices/foil/chart/flex_module

And, yes, Nico is a big boy and pushing a lot harder and faster than most anyone on this forum.

regal1
NSW, 342 posts
7 Dec 2021 1:02PM
Thumbs Up


Nico's foil mast was ventilating. Cavitation damage can be extraordinary as shown above.

Sandman1221
1971 posts
7 Dec 2021 11:09AM
Thumbs Up

Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate shock waves that may damage machinery.

Tell me why the air bubbles you see in Nico's video can not be due to cavitation? Cavitation does not have to lead to shock waves, only when subjected to higher pressure.

aeroegnr
729 posts
7 Dec 2021 11:16AM
Thumbs Up

Select to expand quote
Sandman1221 said..
Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate shock waves that may damage machinery.

Tell me why the air bubbles you see in Nico's video can not be due to cavitation? Cavitation does not have to lead to shock waves, only when subjected to higher pressure.


There's something called a cavitation parameter which is explained in books by Blevins and other authors. Interesting guy, had a course with him. At a certain point the flow is so fast that you get cavitation. It's sensitive to the vapor pressure of the fluid and the depth, among other things. Tip speed in ship propellers are governed by this. There are ways to play around with when this sets in and how much damage it causes...

This looks like a different phenomenon. Because the foil is already connected with the surface, it can suck in air without cavitation. You really should watch this video to see how quickly it can happen. They had to slow down the video to show how it comes from the surface and suddenly the whole foil is now seeing air instead of water. The papers I've posted above/elsewhere show that this can be sensitive to surface roughness, just like pipes and other fluid elements if you look up the Moody chart, but this is more dramatic because it's two-phase flow.


Sandman1221
1971 posts
7 Dec 2021 11:16AM
Thumbs Up

Ventilation occurs when air gets sucked down to the lifting surfaces. Although ventilation can occur on vertical struts, 'V' foils are particularly prone to this problem because of the shallow angle the foil makes with the water surface.

In other words, ventilation is not something that normally happens on a vertical foil mast. You guys are just throwing stuff out there to cover up the fact that there is a design/construction problem with some of the iQ foils.

And, When cavitation occurs, the foil no longer generates enough lift and the boat crashed down onto the water. So cavitation does occur with foils, and that is exactly what you see with Nico, cavitation followed by the board crashing to the water. Ventilation would in comparison be a more gradual process on a vertical mast, and you would see the air getting sucked down the side of the mast, but you do not see that in Nico's video, instead you see an expansion of air bubbles below the water due to cavitation.

Bellerophon
34 posts
7 Dec 2021 3:29PM
Thumbs Up

Select to expand quote
Sandman1221 said..
Ventilation occurs when air gets sucked down to the lifting surfaces. Although ventilation can occur on vertical struts, 'V' foils are particularly prone to this problem because of the shallow angle the foil makes with the water surface.

In other words, ventilation is not something that normally happens on a vertical foil mast. You guys are just throwing stuff out there to cover up the fact that there is a design/construction problem with some of the iQ foils.

And, When cavitation occurs, the foil no longer generates enough lift and the boat crashed down onto the water. So cavitation does occur with foils, and that is exactly what you see with Nico, cavitation followed by the board crashing to the water. Ventilation would in comparison be a more gradual process on a vertical mast, and you would see the air getting sucked down the side of the mast, but you do not see that in Nico's video, instead you see an expansion of air bubbles below the water due to cavitation.



Seems to me you are clearly on some kind of "mission" against SB ( not only in this thread) .
So tell us what is you're actual expirience on the SB IQ foil in general, and, -more specifically- the conditions in which Prien sailed.

Otherwise, you're just speculating.

thedoor
1543 posts
7 Dec 2021 11:04PM
Thumbs Up

Select to expand quote
aeroegnr said..
Interesting thoughts from Nico Prien on his Defi Wind crash. I think this is the best explanation of a potential problem causing a sudden crash, and a remedy. I don't think that this is what happened to cause my crash at my first post in this thread, but I've had some crashes that seemed to act more like what he shows here.





That is very interesting. The fish foil session where i experienced at least a half a dozen non breaching violent catapults was actually the first day I used a brand new carbon foil (of course not sanded). My only explanation was hitting fish as a felt a soft "impact" with each catapult. Perhaps Nico's ventilation theory is more accurate.

Sandman1221
1971 posts
8 Dec 2021 12:38AM
Thumbs Up

Select to expand quote
Bellerophon said..


Sandman1221 said..
Ventilation occurs when air gets sucked down to the lifting surfaces. Although ventilation can occur on vertical struts, 'V' foils are particularly prone to this problem because of the shallow angle the foil makes with the water surface.

In other words, ventilation is not something that normally happens on a vertical foil mast. You guys are just throwing stuff out there to cover up the fact that there is a design/construction problem with some of the iQ foils.

And, When cavitation occurs, the foil no longer generates enough lift and the boat crashed down onto the water. So cavitation does occur with foils, and that is exactly what you see with Nico, cavitation followed by the board crashing to the water. Ventilation would in comparison be a more gradual process on a vertical mast, and you would see the air getting sucked down the side of the mast, but you do not see that in Nico's video, instead you see an expansion of air bubbles below the water due to cavitation.





Seems to me you are clearly on some kind of "mission" against SB ( not only in this thread) .
So tell us what is you're actual expirience on the SB IQ foil in general, and, -more specifically- the conditions in which Prien sailed.

Otherwise, you're just speculating.



Are you affiliated with StarBoard in any way Bellerophon? I am just trying to help aeroengr and others figure out why their iQ foils are dropping them out of flight for no apparent reason.

Sandman1221
1971 posts
8 Dec 2021 12:45AM
Thumbs Up

Select to expand quote
thedoor said..

aeroegnr said..
Interesting thoughts from Nico Prien on his Defi Wind crash. I think this is the best explanation of a potential problem causing a sudden crash, and a remedy. I don't think that this is what happened to cause my crash at my first post in this thread, but I've had some crashes that seemed to act more like what he shows here.






That is very interesting. The fish foil session where i experienced at least a half a dozen non breaching violent catapults was actually the first day I used a brand new carbon foil (of course not sanded). My only explanation was hitting fish as a felt a soft "impact" with each catapult. Perhaps Nico's ventilation theory is more accurate.


Look no one has shown that lightly sanding the mast of an iQ foil stops it from dropping someone out of flight, that includes Nico and aeroegnr. So why doesn't someone who has been having the problem sand their mast down and find out? Better yet contact Starboard to see if they recommend doing that and if it will invalidate any warranty claim.

And again, there is no video evidence from the videos that the mast is ventilating (air snaking down the mast), which by the way does not normally occur on a vertical mast and would not drop you out of flight suddenly like cavitation does.

Paducah
1862 posts
8 Dec 2021 1:20AM
Thumbs Up

Select to expand quote
thedoor said..
That is very interesting. The fish foil session where i experienced at least a half a dozen non breaching violent catapults was actually the first day I used a brand new carbon foil (of course not sanded). My only explanation was hitting fish as a felt a soft "impact" with each catapult. Perhaps Nico's ventilation theory is more accurate.


People who have hit fish have also mentioned that the fish oil/body parts disturb the water flow similar to dirty finger prints. I wonder if that contributed to your day after your first fish encounter?

thedoor
1543 posts
8 Dec 2021 1:26AM
Thumbs Up

Select to expand quote
Paducah said..

thedoor said..
That is very interesting. The fish foil session where i experienced at least a half a dozen non breaching violent catapults was actually the first day I used a brand new carbon foil (of course not sanded). My only explanation was hitting fish as a felt a soft "impact" with each catapult. Perhaps Nico's ventilation theory is more accurate.



People who have hit fish have also mentioned that the fish oil/body parts disturb the water flow similar to dirty finger prints. I wonder if that contributed to your day after your first fish encounter?


I never saw evidence of fishyness on the foil but I don't see finger prints either

duzzi
712 posts
8 Dec 2021 1:46AM
Thumbs Up

Select to expand quote
aeroegnr said..
It makes me feel better about my own crashes and struggles. Gorgeous scenery and great skill at the end with following swells.

A question though: what is causing the sudden board drop to the water in places like at 1:48? Is it just a sudden overfoil or what?
I've crashed like that and it always puzzles me. Most of my overfoils are far more gentle and the board returns me to flight quickly, but sometimes the board will suddenly pitch down like that and I start making up stories about why it happened. Like, did I hit a fish or something? But I really don't know.

The short video afterward is me crashing. You can see the boom twist before I hit the water because my mast broke above the boom head right then. But, I still don't understand that sudden drop. I've accidentally gotten air in gusts and came down slower than that and rode it out without crashing. But this is like a foil-assisted nosedive.






But really, why go through that amount of pain?

Sandman1221
1971 posts
8 Dec 2021 2:12AM
Thumbs Up

aeroengr said, "But this is like a foil-assisted nosedive.", and you are right, the foil is cavitating and so suddenly losing lift causing the board to immediately drop out of flight, that is the hallmark of cavitation, not ventilation. For what you paid for the foil I would be talking with whoever sold it to you and to SB, of course they could be the same. You have a defective foil buddy, wake up and get a replacement if it is a construction issue, and SB should know which it is.

WsurfAustin
227 posts
8 Dec 2021 2:33AM
Thumbs Up

I've hit fish (alligator gar) and ducks. Ducks are a soft bump, while the gar was a hard "clack" like hitting a concrete curb. No crash with the duck, total face plant with the gar. Only time I crash in loss of laminar flow is motor boat prop wash.

WsurfAustin
227 posts
8 Dec 2021 2:33AM
Thumbs Up

I've hit fish (alligator gar) and ducks. Ducks are a soft bump, while the gar was a hard "clack" like hitting a concrete curb. No crash with the duck, total face plant with the gar. Only time I crash in loss of laminar flow is motor boat prop wash.

aeroegnr
729 posts
8 Dec 2021 3:22AM
Thumbs Up

Select to expand quote
WsurfAustin said..
I've hit fish (alligator gar) and ducks. Ducks are a soft bump, while the gar was a hard "clack" like hitting a concrete curb. No crash with the duck, total face plant with the gar. Only time I crash in loss of laminar flow is motor boat prop wash.



The area that I filmed this in actually is the same area that I saw a HUGE sea turtle. There's dolphins there too. I think the only thing I've hit are stingray. That may have been what precipitated the crash that started this thread because there are hundreds there and they are mostly invisible until you're right ontop of them or they jump out of the water. Haven't had anything but scratches on the foil and foil mast.



















gorgesailor
497 posts
8 Dec 2021 4:57AM
Thumbs Up

Select to expand quote
Sandman1221 said..
Ventilation occurs when air gets sucked down to the lifting surfaces. Although ventilation can occur on vertical struts, 'V' foils are particularly prone to this problem because of the shallow angle the foil makes with the water surface.

In other words, ventilation is not something that normally happens on a vertical foil mast. You guys are just throwing stuff out there to cover up the fact that there is a design/construction problem with some of the iQ foils.

And, When cavitation occurs, the foil no longer generates enough lift and the boat crashed down onto the water. So cavitation does occur with foils, and that is exactly what you see with Nico, cavitation followed by the board crashing to the water. Ventilation would in comparison be a more gradual process on a vertical mast, and you would see the air getting sucked down the side of the mast, but you do not see that in Nico's video, instead you see an expansion of air bubbles below the water due to cavitation.


Wrong

Ian K
WA, 3969 posts
8 Dec 2021 7:02AM
Thumbs Up

I'd think cavitation bubbles would collapse back into liquid water once the low pressure zone was passed. Isn't the collapsing of the bubbles what causes damage? Ventilation looks like it originates at a tip vortex, If the tip vortex reaches the surface somewhere in the wake it can hollow out all the way back to its source. You wouldn't easily see this looking at the wake from the surface. Not sure about hydrophobia??



Looks like cavitation at about 3 minutes just behind the leading edge. Not sure what they are calling what looks like the tip vortices earlier in the video? Maybe tip vortices can spin up fast enough so the the pressure at the centre of the vortex is lower than the vapour pressure of the fluid.

Sandman1221
1971 posts
8 Dec 2021 7:31AM
Thumbs Up

Select to expand quote
gorgesailor said..

Sandman1221 said..
Ventilation occurs when air gets sucked down to the lifting surfaces. Although ventilation can occur on vertical struts, 'V' foils are particularly prone to this problem because of the shallow angle the foil makes with the water surface.

In other words, ventilation is not something that normally happens on a vertical foil mast. You guys are just throwing stuff out there to cover up the fact that there is a design/construction problem with some of the iQ foils.

And, When cavitation occurs, the foil no longer generates enough lift and the boat crashed down onto the water. So cavitation does occur with foils, and that is exactly what you see with Nico, cavitation followed by the board crashing to the water. Ventilation would in comparison be a more gradual process on a vertical mast, and you would see the air getting sucked down the side of the mast, but you do not see that in Nico's video, instead you see an expansion of air bubbles below the water due to cavitation.



Wrong


And your source of information?, I just copied that from a hydrofoil website, and they should know!

aeroegnr
729 posts
8 Dec 2021 7:42AM
Thumbs Up

To clarify: cavitation is when the pressure from the lifting surface gets so low on the suction side that it gets close to the vapor pressure of the fluid. Close enough and you get gas vapor bubbles. Proportional to velocity squared. It's what damages props from bubble collapse, yes.

Ventilation is when the free surface of the liquid (water surface in this case) gets pulled down and contacts the lifting body. Yes you can ventilate from a tip vortex, but that's not as severe as the earlier video I posted.

That video shows a vertical foil, like a mast in this instance, flashing from fully contained in water to pulling in a bubble on the suction side in a split second. What it doesn't show is the connection it can possibly make with the fuselage and stab, possibly causing the stab to see air not water then bam, no lift. Probably also causes spinout if the mast was providing Lateral resistance.
Or since the mast is suddenly seeing 1000kg/m3 water on one aide and 1.25kg/m3 air on the other side, it just makes the spinout worse and that's enough to cause a crash without ventilating the stab.

I posted a paper in the other thread that shows that ventilation of a hydrofoil is sensitive to surface roughness. So, it's very plausible, especially when you see Nico's board yaw with a change in spray direction.

gorgesailor
497 posts
8 Dec 2021 8:15AM
Thumbs Up

Select to expand quote
Sandman1221 said..

gorgesailor said..


Sandman1221 said..
Ventilation occurs when air gets sucked down to the lifting surfaces. Although ventilation can occur on vertical struts, 'V' foils are particularly prone to this problem because of the shallow angle the foil makes with the water surface.

In other words, ventilation is not something that normally happens on a vertical foil mast. You guys are just throwing stuff out there to cover up the fact that there is a design/construction problem with some of the iQ foils.

And, When cavitation occurs, the foil no longer generates enough lift and the boat crashed down onto the water. So cavitation does occur with foils, and that is exactly what you see with Nico, cavitation followed by the board crashing to the water. Ventilation would in comparison be a more gradual process on a vertical mast, and you would see the air getting sucked down the side of the mast, but you do not see that in Nico's video, instead you see an expansion of air bubbles below the water due to cavitation.




Wrong



And your source of information?, I just copied that from a hydrofoil website, and they should know!


From another Hydrofoil website ... though your source also mentions the speed at which cavitation occurs: "Cavitation and ventilation both appear as bubbles attached to the surface of the operating hydrofoil. This phenomenon particularly occurs over the section back (suction side) of the hydrofoil with the bubbles varying both as to size and extent. The formation of vapor bubbles will occur within a liquid in a region where the static pressure of the liquid's flow field is equal to, or less than, the saturation (vapor) pressure of the liquid. The resulting low pressure is a consequence of the local acceleration of the liquid to a relatively high velocity over the hydrofoil surface. In order for cavitation to develop, the surface pressures on the suction side of the hydrofoil must be lower than water vapor pressure. Ventilation will develop when surface pressures exist which are lower than the ambient pressure of an externally available gas supply. The gas supplied is usually air from an atmospheric source. Cavitation invariably occurs in conventional hydrofoil craft above a certain operating speed (typically over 50-60 knots). Ventilation can occur at much lower speeds."

So it is much more likely ventilation is causing the issues than cavitation considering the speeds Windfoil are currently capable of...

Ian K
WA, 3969 posts
8 Dec 2021 8:52AM
Thumbs Up

Select to expand quote
aeroegnr said..
Proportional to velocity squared. It's what damages props from bubble collapse, yes.

Well for a given surface radius of curvature it is. If you can reduce the radius of curvature cavitation is delayed. Well that's the interpretation you'd make from Regal 1's Gitana video. They mention that thinning the foils will delay cavitation but then they'd run out of structural strength to hold up the weight.

boardsurfr
WA, 1603 posts
8 Dec 2021 9:09AM
Thumbs Up

Select to expand quote
gorgesailor said..
Cavitation invariably occurs in conventional hydrofoil craft above a certain operating speed (typically over 50-60 knots). Ventilation can occur at much lower speeds."


The "invariably" is important - there's simply no way around it once you go fast enough, so you need a different design, like the Sailrocket 2 used.

That does not mean cavitation can't occur earlier - it certainly will occur earlier in sub-optimal conditions.
Select to expand quote
gorgesailor said..
In order for cavitation to develop, the surface pressures on the suction side of the hydrofoil must be lower than water vapor pressure.

Ventilation will develop when surface pressures exist which are lower than the ambient pressure of an externally available gas supply. The gas supplied is usually air from an atmospheric source.


Water vapor pressure is around 5 hPa at room temp, while air pressure is about 1000 hPa. That would mean that ventilation would occur a lot earlier.

Do I assume correctly that ventilation requires some kind of "connection" to the "externally available gas supply"? A foil mast obviously always has such a connection.

What is the speed with which ventilation can spread? In windsurf fin design, especially for weedies and deltas, advanced designs have some characteristics that aim to minimize the spread of ventilation to the lower part of the fin.

What about cutouts? Probably ventilated, not "cavitated"? If cavitation damages propellers, then it certainly would damage glass fiber hulls?

Sandman1221
1971 posts
11 Dec 2021 8:34AM
Thumbs Up

Select to expand quote
Paducah said..





Grantmac said..
I've actually held AFS and IQ foil setups, the AFS is very flexible in comparison. Even the regular Starboard setup is significantly stiffer.





Yes and not really. In torsion, the orig 95 and AFS are very close but the IQ is much stiffer. In flex (side to side), the AFS is significantly stiffer than the orig or IQ.

windfoilfan.glissattitude.com/devices/foil/chart/tors_module

windfoilfan.glissattitude.com/devices/foil/chart/flex_module

And, yes, Nico is a big boy and pushing a lot harder and faster than most anyone on this forum.



According to windfoilfan data, the 2019 AFS W95 foil is the 4th stiffest/most rigid mast behind 1st 2021 F4 slalom race, 2nd 2019 Phantom Iris, and 3rd 2018 AFS W105!

Sandman1221
1971 posts
11 Dec 2021 8:43AM
Thumbs Up

Select to expand quote
Sandman1221 said..

gorgesailor said..


Sandman1221 said..
Ventilation occurs when air gets sucked down to the lifting surfaces. Although ventilation can occur on vertical struts, 'V' foils are particularly prone to this problem because of the shallow angle the foil makes with the water surface.

In other words, ventilation is not something that normally happens on a vertical foil mast. You guys are just throwing stuff out there to cover up the fact that there is a design/construction problem with some of the iQ foils.

And, When cavitation occurs, the foil no longer generates enough lift and the boat crashed down onto the water. So cavitation does occur with foils, and that is exactly what you see with Nico, cavitation followed by the board crashing to the water. Ventilation would in comparison be a more gradual process on a vertical mast, and you would see the air getting sucked down the side of the mast, but you do not see that in Nico's video, instead you see an expansion of air bubbles below the water due to cavitation.




Wrong



And your source of information?, I just copied that from a hydrofoil website, and they should know!


That hydrofoil information came from the Massachusetts Institute of Technology (MIT) website.



Subscribe
Reply

Forums > Windsurfing Foiling


"Awesome video by Andy Laufer, and a crash question. Overfoiling or no?" started by aeroegnr