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.

Sandman1221 said..
I think it has to do with how strong the gust is that makes you foil out, moderate gust and you foil out and then loose lift from the foil and nose dive with sail perpendicular to the water, strong gust and you will actually fly into the air with sail parallel to the water and board at a right angle to the water.

If that's a gust, how do you react to it? The crashes to me that seemed like gusts all had much much longer time to react.

Mmm love those unhooked buckn bronco rides. They make me feel all warm and fuzzy.


Its pretty hard to tell from either video what exactly causes the stack. It's possible the foil ventilated from being loaded the wrong way, but that's really a wild stab in the dark. It's happened to me before, largely because I was carrying too much mast foot pressure, and had a sh!t stance (ok, I still do). You can usually tell if it's wrong cause the foil will gurgle just foiling along, telling you that it's struggling to keep the flow attached. Aside from causing a stack, it's not fast either.

but that really is a wild guess. Could very well be not what caused the stack.

Just gotta love how he always puts the pedal to the metal!!!!!!

I won't buy any of his used gear though.

Re the 1.48 crash. Based on a recent session, I think it's possible for some faster foils to stall without breaching and you basically plumet in the same way as a breach. I only experienced this on a fast foil that was not dialled in.



It was a super frustrating day, I must have had 10 of these non-breach crashes, went winging the next few days in protest

aeroegnr said..

thedoor said..
Re the 1.48 crash. Based on a recent session, I think it's possible for some faster foils to stall without breaching and you basically plumet in the same way as a breach. I only experienced this on a fast foil that was not dialled in.

It was a super frustrating day, I must have had 10 of these non-breach crashes, went winging the next few days in protest

Very interesting! And you caught it on video where it's clear that the foil isn't out because you can see that you're not at the end of the mast.

At least it feels like WORSE than a stall. I think somehow the wing actually goes from positive to negative lift? In that mast break video I can see the board move downward (need to step forward slowly on Youtube with the period key) so fast that my legs go straight and I come out of the harness, but get rehooked just in time to snap the mast. I really think the board if moving downward faster than gravity is pulling it otherwise I would just fall at the same speed as the board and it would look different...Maybe the front wing isn't stalling but the rear one is for some reason? It may be possible that the back wing stalls, kill the positive pitch of the system, and then the front wing gets negative AoA and boom, into the water you go. But...again, how do we prevent this? I'm speculating that it's a REAR WING stall, not a front wing stall. Hmmm... Maybe it is just a stance thing that somehow loads the rear wing up? I would have to sit there and do a force balance diagram to see if that even makes sense..

By the way, I went out today after watching this new Duotone video. That demonstration of hip movement made a big difference with control. Somewhat related. I think that my stance was more rear with the front leg more straight when I wanted to fly lower.

Yeah stall may not be the right word. I was using 111 mast that day doing about 21knots and preceding every "wet foil crash" I felt a soft thud, felt like a big fish.

Maybe if I hit that fish at the bottom of the mast and the leverage of overcame the lift of the foil and tilted the whole thing down? as I said it was the first time I was trying that ghostwhisper foil and it wasn't set up right so I was really back footed which I interpret as too little lift or lift not forwards enough

Thanks aeroengr for the duotone video, will have to pay attention to my hips next time to see what I do with them. As for the stall issue, have never had that problem on the AFS W95 with the F series wings, the only thing close to that is when I hit a sea creature, but that feels like I hit an under water pylon. maybe the wing on your foil is cavitating?, that would cause a loss of lift, same can happen in windsurfing with the fin cavitating and causing a spin out.

Whistle tuning :
BAD :


GOOD :


Just any wing stalls at when above stall AOA whatever the speed.
Water can be a very messy fluid close to the water, with up and down draft and whirling movements. I usually try to fly low so the wing is in deeper laminar water.

aeroegnr said..

The first one looks like a different kind of crash.

Don't take my video too seriously ! That's definitely not the point. Just some fun 'tuning the whistle'...

aeroegnr said..Looks like the left wingtip came out and started that one.

Here you're right. Good, I didn't even bothered to slow motion this crash. Now I know what went wrong (other than I was just pushing my limits...). Another reason to keep it low if possible. If I remember well, I was riding a XL (aeromod) wing. Rather high ratio, so probably not very forgiving in case of partial wing breaching.

aeroegnr said..You're right about stalling though.

I would be shameful not to be. Part of my job to know that. A stalled stab could explain some odd foil behavior. I doubt it though. Foil designers certainly foresaw this matter and the stab must be working at rather low AOA.
Many factor can be involved, from water surface whirl to elastic fuselage springing back to position after a sudden load on the stab (the gust with a massive pushdown from the sail)

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.



Also interesting is someone posted/maybe deleted this comment on the video. It shows a sudden flash of ventilation over the entire length of the foil when the conditions are right. They do a slow motion cut as well to show the progress, although out there in reality it would feel instantaneous.

Sandman1221 said..
First with my AFS W95 foil I only crash if I foil out or hit something. But I do feel waves slap the side of the mast, and bigger waves (2-3') will noticeably push the foil and me around, but no crash follows. So I watched Nico's video about the surface of a carbon mast being hydrophobic or not, checked my AFS W95 mast and it was hydrophobic!, and I have never sanded it.

So aeroengr maybe the issue is your mast and/or fuselage is twisting due to changes in water pressure on the foil due to currents in the water, or how sail pressure is being transmitted to the foil, or as I mentioned above a wave is slapping the side of the mast. The AFS W95 mast and fuselage are both really stiff, and since there is no bolted joint between the two that makes the foil even stiffer.

I think it would be easy to see why a twisting mast/fuse. would cause a crash, since the wing/stab. would go out of alignment and cavitate instantly.

If you want to try out my AFS foil and see, just pm me and we can figure out a time and place, this coming Wed. and more so next weekend look promising for wind.

Thank you! I honestly haven't had problems lately, I really think it was just needing to go faster plus having more heel on the board.

I think I really need to setup my boom cam next time I ride the IQ to see how much things have changed (or not?). I usually have the helmet setup because it's easier.

I don't think I'm over the mast more unless going downwind. I'm a lot more in the harness than I was. The twist of that I don't think is the problem because the IQFoil mast is pretty stiff as is. There is flex in it but everything is a design compromise. I just know that I haven't had that loose spin-out feeling in a while because I've been riding different. I only get close if I ride too high, which tends to happen more along the jibes now than anything.

Sandman1221 said..

aeroegnr said..
I think I really need to setup my boom cam next time I ride the IQ to see how much things have changed (or not?). I usually have the helmet setup because it's easier.

I don't think I'm over the mast more unless going downwind. I'm a lot more in the harness than I was. The twist of that I don't think is the problem because the IQFoil mast is pretty stiff as is. There is flex in it but everything is a design compromise. I just know that I haven't had that loose spin-out feeling in a while because I've been riding different. I only get close if I ride too high, which tends to happen more along the jibes now than anything.

Mast can be the stiffest on earth, but if the connection to fuse. flexes than it does not matter. And an aluminum fuse. can fatigue over time and flex more, especially after being over stressed repeatedly like in a crash. I wonder how often PWA foilers replace their aluminum fuselages.

and if you want to find out if your mast is actually stiff, all the info is here, torsion and bend deflection tests

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

Sandman1221 said..
The other explanation for Nico's foil generating air behind the mast, is the wing was flexing a fatigued fuselage and that in turn was twisting the mast. He said his regular fuse. was being worked on, maybe it was being replaced, and he had to use an old fuse. that was fatigued.

I don't think that's it. If it's moving enough to flex more than usual from fatigue, that means it is cracked, and would likely very quickly destroy itself afterward. The modulus doesn't drop like that.

Bellerophon said..
He said he changed the foil MAST, not the fuselage..

And that is indeed what the video of his crash shows, if you look at it in slow motion. Here's a screen shot about 1 second before things go wrong:



Note the angle of the board. Nico's body position is too the outside, so he is putting considerable sideways pressure on the mast.
Here's a screen shot from a second later:


The angle of the board has changed a lot. The back leg is now more extended than the front leg. This happened because the mast cavitated, and could not hold the sideways pressure anymore - so it slipped to the side. Anyone using a 60 cm mast with a Slingshot foil will be used to this feeling. I've seen a top-level foil instructor have nasty catapults after such a "spin out".

As for why Nico catapults after the mast cavitates, it's easy to come up with theories. For example, the air bubble could have extended from the mast to the foil, like in the second video aeroengr posted. Or the foil may have lost lift because it suddenly was at a ~ 25 degree angle to the direction of travel. Or he simply had too much of his weight on his front foot when the back leg extended, so the sail pulled him over the front. But it does not really matter how exactly he crashed. Recovering from a mast suddenly slipping to leeward while fully powered, probably going 30+ knots, seems like a near-impossible thing to do.

Nice work from Nico to discover the cause of his crashes, and to explain things nicely in the video. Thanks to aeroengr for posting the vids.

boardsurfr said..

Bellerophon said..
He said he changed the foil MAST, not the fuselage..

And that is indeed what the video of his crash shows, if you look at it in slow motion. Here's a screen shot about 1 second before things go wrong:



Note the angle of the board. Nico's body position is too the outside, so he is putting considerable sideways pressure on the mast.
Here's a screen shot from a second later:


The angle of the board has changed a lot. The back leg is now more extended than the front leg. This happened because the mast cavitated, and could not hold the sideways pressure anymore - so it slipped to the side. Anyone using a 60 cm mast with a Slingshot foil will be used to this feeling. I've seen a top-level foil instructor have nasty catapults after such a "spin out".

As for why Nico catapults after the mast cavitates, it's easy to come up with theories. For example, the air bubble could have extended from the mast to the foil, like in the second video aeroengr posted. Or the foil may have lost lift because it suddenly was at a ~ 25 degree angle to the direction of travel. Or he simply had too much of his weight on his front foot when the back leg extended, so the sail pulled him over the front. But it does not really matter how exactly he crashed. Recovering from a mast suddenly slipping to leeward while fully powered, probably going 30+ knots, seems like a near-impossible thing to do.

Nice work from Nico to discover the cause of his crashes, and to explain things nicely in the video. Thanks to aeroengr for posting the vids.

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.