Standup Zone Forum

The Foil Zone => Wingsurfing, Windfoiling, Wingfoiling, Wing SUP => Topic started by: Solent Foiler on October 25, 2021, 04:47:58 AM

Title: Getting ejected out the front door...
Post by: Solent Foiler on October 25, 2021, 04:47:58 AM
Would like to understand why I get ejected out the front door.
Usually when I'm cranking upwind, loaded up in the harness, and I then feel something ventilate and usually ends up in a roll to windward, (so not a sudden, catastrophic loss of lift, / nose dive as you would over foiling)

Weirdly happens on flat'ish water as well as choppy.

I thought it might be something to do with the Gong Fluid foils, as it didn't happen so much with the Veloce, but it happened a few times yesterday on my brand new, perfect condition ART 999 and 380 tail, so I wonder if it's the mounting of the tail on top of the fuse rather that the middle, as the Veloce tails are. But the Veloce tail was a bit bigger too...

Clearly I'm the rider so will take responsibility for the crashing, but I feel a bit cheated as I don't feel like I'm making an obvious mistake. I wonder if it's a chop thing, because it does feel like a white cap, hits the mast and then it happens, but could be my imagination? Also, on a 1m wide wing can air get all the way down to the tail to cause ventilation without also causing a main foil tip breach? Is air going down the mast, down the fuse, to the tail? Feels unlikely... Am I loading up the tail too much and causing it to 'spin out' (upwards/negatively)?

I don't think it's a main foil issue for various reasons but could be that too?

Thoughts, comments, suggestions welcome...
Title: Re: Getting ejected out the front door...
Post by: Funsup on October 25, 2021, 05:55:41 AM
Iíve experienced the same issue with other black fuselage foils on a carbon mast. Different lengths of masts or fuselages did not alleviate the problem.  Charging upwind and chop slaps the side of the mast, then the foil momentarily loses lift on the up wind side causing me to lose balance and start falling upwind.  Sometimes I can save it and sometimes I just explode.  I would like to know how to eliminate this problem as well but have not found the solution yet.  I donít ever recall having the issue on any of the red fuselage foils.
Title: Re: Getting ejected out the front door...
Post by: PonoBill on October 25, 2021, 06:23:59 AM
Sounds like ventilation. We're ALL going to have this problem as we start going faster. It may be that the 19mm Axis mast is a bit more prone to it than skinnier masts but it's a phenomenon hanging out there waiting to plague anyone that pushes hard and goes fast. That doesn't generally include me, though I've had a few unpleasant moments with the 1300 wing.

Presently I don't know of any mast that combats this. Tapered carbon masts should be less prone to it. Thick aluminum masts will probably be the worst. I made a little fence to try adding on to my mast. I haven't installed it yet, and I expect it's too big, but high-performance masts will probably be going that way. The pic shows a stub of a mast with the fence temporarily hot glued to it.

It's a huge problem for really fast foiling sailboats. Some people think it represents a barrier to going faster than 50 kts. Outboard motors add ventilation plates to the masts, some high-performance ones have multiple plates.

Something new to screw with.
Title: Re: Getting ejected out the front door...
Post by: Dwight (DW) on October 25, 2021, 06:42:24 AM
Is your foil kit perfectly balanced at any speed? Meaning, your foot pressure balance is the same at low speed and high speed?

Mine is, and this never happens to me. Itís the only wild idea I can come up with.

Iím real particular about getting this balance/low drag setup spot on. I never have back foot or front pressure at any speed.

Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on October 25, 2021, 06:46:20 AM
Just to pre-empt the conversation  :P (Copied from Google):

"Ventilation occurs when part of a hydrofoil pierces the surface of the water and air gets sucked down the lifting surface of the foil. Since air is much less dense than water, the foil generates much less lift and the boat crashes down. Ventilation can occur at any air-water interface."

"Cavitation occurs when the water pressure is lowered to the point where the water starts to boil. ... When cavitation occurs, the foil no longer generates enough lift and the boat crashed down onto the water."
Title: Re: Getting ejected out the front door...
Post by: Hdip on October 25, 2021, 08:28:17 AM
Are you pushing sideways through the water when you fall? You say it's like you lose pressure on one side of the wing. The windward side? So if you're leaned over into the wind that sounds to me like you are talking about the side of the front wing that is deeper in the water. You also mention it happens on several different front wings.

That doesn't sound like front wing ventilation to me. It sounds like mast ventilation. The mast is a lifting surface too.

Is this what you're describing?

https://www.youtube.com/watch?v=BlCuVZK2aqE
Title: Re: Getting ejected out the front door...
Post by: seastudent on October 25, 2021, 08:44:48 AM
Is your foil kit perfectly balanced at any speed? Meaning, your foot pressure balance is the same at low speed and high speed?

Mine is, and this never happens to me. Itís the only wild idea I can come up with.

Iím real particular about getting this balance/low drag setup spot on. I never have back foot or front pressure at any speed.
Have you or could you post the process to achieve this? I used The KD balance method to start but my tuning seems to be pretty scattershot. Usually I try frowning and some incantations but that doesn't seem real effective.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on October 25, 2021, 09:18:44 AM
Is your foil kit perfectly balanced at any speed? Meaning, your foot pressure balance is the same at low speed and high speed?

Mine is, and this never happens to me. Itís the only wild idea I can come up with.

Iím real particular about getting this balance/low drag setup spot on. I never have back foot or front pressure at any speed.

I didn't even think this was possible?! I always get more pressure on the front foot as speed increases. The thinner foils (Veloce, 999) less so, but how do you do it? Matching front and rear foils so they have the same lift profile over all speeds? Doesn't that limit stab choice?

To be absolutely explicit about the circumstances:

Flat water : hauling ass, fully loaded, canted over, going upwind. Seems a bit spontaneous when it happens, although I do get a bit of warning sometimes, and if I back off a little it seems to be better (but where's the fun in backing off?!?) Might be in conjunction with hitting a gust.

Moderate chop :  going fast upwind (but not as fast as flat water), canted over, feels like chop hits mast and down I go. Like Funsup says, sometimes the roll to windward is slow enough to catch and recover, often not...

I'm beginning to convince myself of the overloading tail hypothesis. In both circumstances, the tail is under rotational load, pivoting around the front foil with the force coming from the wing driving the whole system forward at a point about 2m above. I think the very thin profile of the 380 and Fluid tails mean they are less able to cope with an AOA that is not straight on, so when the force from the wing starts pulling forward and pushing the nose down down (rotating forward), the AOA changes so that it becomes more likely to stall and loses grip. Obviously the drag on the tail goes up rapidly as it gets pushed through the water flat face first as everything rotates around the front foil, so the crash is slower than might be expected as the whole thing doesn't nose dive like having the tail snap off, for example.

The Veloce tail actually has more volume and profile shape, which might explain why it doesn't suffer from this.

The choppy water could just be introducing turbulent water to the tail, again changing the AOA or introducing air so it tips it over and loses grip.

I'm fairly sure the whole thing is related to cant too, but can't figure it out. I've adopted a defence against this ventilation issue from happening by keeping the mast more vertical, but it's a compromise.

Am I making any sense? Tell me I'm wrong, because I'd love to understand what's going on. I've got a couple things in mind to try...

Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on October 25, 2021, 09:25:51 AM

Is this what you're describing?


Possibly in terms of effect, but that's a more extreme situation and I don't think I get nearly the same lift from the mast as they do, especially as I run an 85cm mast and in one instance the 999 so limited as to how far over I can go to get the mast lifting.

It's a good suggestion though. Hadn't considered it!

I agree that the front foil, especially the windward tip isn't the issue...
Title: Re: Getting ejected out the front door...
Post by: jondrums on October 25, 2021, 10:51:22 AM
I have a theory -

When going upwind, you need side force to counteract the pull of the wing.  In a sailboat, the centerboard/daggerboard/keel react this load and keep the boat from going sideways.

On a windfoil setup, there are actually two ways you could counteract side force - 1) the mast in the water acts as a daggerboard 2) if the foil is tilted/heeled over, then the front wing lift has a side force component.

My theory is that you are riding the board too upright and using the mast to gain sideforce reaction.  Perhaps it would work better if you concentrate on heeling the board/foil over to windward and using the lift of the foil instead.  The mast can easily ventilate because it pierces the air/water boundary, but the foil won't if it stays underwater.  If you take a look at foiling sailboats, they all heel to windward in order to use the main foil for side-force.
Title: Re: Getting ejected out the front door...
Post by: Wingfoil2001 on October 25, 2021, 12:25:03 PM
Itís a really common problem when kitefoiling due to the higher speeds. Yes, some masts are more prone to it than others. Att higher speeds the condition of the foil parts is critical, no nicks or damage that could interrupt smooth waterflow across the surfaces.

Clean your foil before going out if your planning to push some speed.  I use window cleaner to remove fingerprints etc to get it perfectly clean then not let anyone touch it. Watch kitefoil racers clean their kit before a race to help prevent ventilation.
Title: Re: Getting ejected out the front door...
Post by: bigmtn on October 25, 2021, 01:23:42 PM
I have what I think is the same issue, mostly while riding toe side and trying to go fast upwind while trying to drop into a wave. It feels like someone underwater just yanks my foil sideways out from under me.  It happens heal side, but I'm usually able to use my toes to push the board back down.  I figured that either the mast is far enough over that it turns into a wing of its own and the side chop causes it to lift, or the mast ventilates causing the same thing. I've gotten to the point where I can feel when I'm in a position/speed/condition where it's about to happen, and can bring the mast down more vertical for a bit to keep it under control. 

I use a 90cm Axis 19mm alu mast, and when I mentioned it to friends on other gear, they hadn't experienced it.  Kind of just figured it was caused by the mast shape. And if my memory is correct, I think Kane mentioned something similar about it in his last progression podcast.
Title: Re: Getting ejected out the front door...
Post by: jondrums on October 25, 2021, 05:46:48 PM
Could well be the mast shape too.  If the leading edge is too sharp flow can separate pretty easily.  Masts foil section probably matters a good bit - maybe axis for something wrong on this respect
Title: Re: Getting ejected out the front door...
Post by: PonoBill on October 26, 2021, 10:37:38 AM
I thought my post was fairly clear that I'm talking about mast ventilation, not wingtips. Masts can actually ventilate in a vertical attitude, though the speeds need to be higher. As you lean them over to turn or go upwind, both the angle relative to the water and the angle of attack of the mast changes, and the mast foil characteristics become more important. Any surface moving through a medium has pressure differentials, airfoils are effective and efficient at creating pressure differentials--it's how they work to lift us. The pressure differentials are a function of surface area times a factor for foil shape times velocity squared. The foil shape factor is empirically measured, but it's got a lot to do with thickness--all other elements being equal, the thicker the foil, the higher the factor.

The Axis aluminum masts are thicker (19mm) and wider than most foil masts on the market. It's why they are so rigid. Every design consideration has consequences, and the designer chooses which characteristics are most important and which to sacrifice. The Axis aluminum mast is ideal for probably 95% of their customers. It's strong, stiff, and cheap. It's also cool looking which is more important than most of us would like to admit. I think it's probably axiomatic that a 19mm, strong, stiff mast is going to ventilate more easily than a 15mm, weak, flexy mast. It's probably feasible to push the 19mm Axis mast ventilation to higher speeds, but it won't be the nice, simple hundred buck mast that we currently have. As far as anyone knows, it's impossible to eliminate ventilation when speeds get high enough. It's the limiting factor on all kinds of high-speed watercraft. It's one reason why the fastest powerboats have weird surface-piercing propellers--the biggest reason is efficiency, but the secondary reason is that submerged drives will ventilate anyways--the designer might as well design for it.

There isn't any element of this situation that is unexpected or new. Most of the basic research on this stuff is 50 to 100 years old. Outboard motors from the 1920's have ventilation plates. Thicker, wider masts ventilate at lower speeds than thin, narrow ones. If you're having trouble with the issue, congratulations, you're pushing your gear to a higher level of performance than most folks. You'll probably get some relief from using the carbon mast, though even a duffer like me can feel some flex with a 999, and lots of flex with a 1150. I've never had a carbon Axis mast ventilate, but your mileage will vary.

Ventilation aside, I still prefer the Axis 19mm mast over anything else. I used a slingshot 15mm X 75cm mast for my boosted foil because the clamp on the motor was designed for that size. That is pretty much the standard aluminum mast for foils, probably everyone gets the extrusion from the same factory and then cuts it to length for their masts. I got my foil and drive system put together, turned the board over, and wiggled the wing around. I was fairly horrified. I can easily rotate the fuselage about 30 degrees and bend it sideways with just hand pressure to about 10 degrees. I know it's going to work anyway, my much heavier Takuma eFoil has the same mast, though it's super short. I now know why it's so short. Riding the Takuma is like driving a car with worn out, loose steering. It takes a while for any control input to actually do something. Not a great thing for precise control.
Title: Re: Getting ejected out the front door...
Post by: Dontsink on October 26, 2021, 11:28:47 AM
KDmaui talks about waxing (with car wax) his setup because it gives him more speed.Roughly 1mph more.

If you ask race sailors they will tell you that a waxed smooth&clean hull is slower than a non waxed one(some surface tension thing)...but the key part is clean&smooth.
Waxed is faster than dirty and scratchy,it smooths the surface and prevents the dirt from sticking.
Serious racers sand and clean their boats like mad before a race, most recreational foilers do not.
We put our foils wet & scratched in a cover to dry out and all the crap that is in the seawater dries out and sticks to the foil.

I have noticed that my foil runs a bit "rough" at the beginning of a session.It feels a bit slower,more sluggish and then gets better.I think it takes a while for all the deposits to soften up and get washed away.
With wax it "feels" good from the beginning.

So maybe it will make your mast perform better,worth a try.
Title: Re: Getting ejected out the front door...
Post by: Beasho on October 26, 2021, 12:09:32 PM
Waxing, sanding, foil shape . . 'we' all went crazy with this in the 90's with windsurfing fins.

With regards to speeds.  I measured the heck out of Surfboard speeds, and foil speeds.  Hundreds of thousands of data points.  My take is this:

1) Winging is relatively SLOW:  Speeds from 7 mph to 18 mph.  More advance wingers are faster.  Johnny Heineken goes 26 mph.   
2) SUP foiling on waves gets faster.  Slow ~ 10 mph.  Fast 20 mph.  Blistering is 25 mph.  BUT the speed is nearly perfectly correlated to wave size.  To go 25 mph you'll need a 10 foot wave or bigger. (not counting a Pipeline type wave which does change/increase the math slightly)
3) A surfboard, or SUP, on an 18 foot wave can hit 30 mph.  To get to 35 mph Mavericks will deliver. 
4) Old school shortboard Windsurfer would plane at 17 mph. (as measured by Speedwatch) FAST was 25 mph.  30 mph was almost unobtainable due to CHOP and required wind speed, flat water . . . hence the world record was in the 30's for a while
5) Kite foils apparently blow this all away (I do not have data).  But 30 mph is supposed to be reasonable for a good kite-foiler.

Winging will get faster.  I will get faster.  Winging will likely converge with Kite foil speeds but we will lose the comfort and sanity of controlled slow speed flight.

PS: My first session on the Axis999, in winds blowing 30 to 40 mph in flat protected water, I recorded speeds of 11 to 13 mph.  Maxed out at 13.4 mph.  And I was OK with this, way overpowered on a 5.0.  But I wasn't ripping past 20 mph on my first session.  For the record I have never knowingly ventilated my mast.
Title: Re: Getting ejected out the front door...
Post by: bigmtn on October 26, 2021, 02:28:40 PM
According to my phone my top speeds per session usually range between 22 - 26 mph.

28.07mph is fastest I've recorded.

Measured using windsport tracker app, who knows how accurate it is.
Title: Re: Getting ejected out the front door...
Post by: PonoBill on October 26, 2021, 03:32:08 PM
You are a bit less likely to ventilate surfing, no matter how fast you go. You are more likely to be vertical and the force that's pushing you through the water is being applied down low, partly to the foil, and to a lesser degree from gravity shoving you down the face of the wave. The amateur physicist in me recoils at saying anything that sounds like "the force of gravity" but don't worry, I'll be okay, I just need to lie down in a dark room for a moment.

At first glance, you might think the speed of the foil through the water is less because the foil is moving at wave speed or thereabouts. But the water doesn't move with the wave. It basically just moves up and down in a little epicycle.

If you fully ventilate your mast you will definitely know it. The wing gets surrounded by a bubble of air. Air is about 1000 times less dense than water. You'll have just about as much lift remaining as you will if you hold the 999 over your head and run down the beach making propeller sounds.

Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on October 28, 2021, 03:24:18 AM
Just to be clear, I'm not chasing high speed, I'm just trying to get upwind as quickly as possible to ride downwind again, so might as well make it fun by pushing as hard as I can, having a harness and all. I don't even record my sessions so have no idea how fast I'm actually going.

But that's sort of the point. I think I'm operating in a fairly conservative envelope when it comes to speed/performance (the 999 is not a speed foil in the grand scheme), so why should I be suffering from this ventilation issue? I'm only 65kg, so can't be loading up my kit as much as bigger riders...

But, I may have found a technique issue yesterday that might be making the problem worse. When I go upwind I normally have my back foot out the strap - it's just more comfortable as I can control the pitch and roll a bit more easily when just blasting in a straight line. I need to take it out for tacking anyway as I swap feet so one less thing to do. If I go upwind with my back foot in the strap, it feels a lot less likely to ventilate and if it does, it's less dramatic and correcting is easier.

I wonder if that stance is giving me more yaw control, so can keep the mast pointing in the direction of travel better than having my back foot forward? Or perhaps just being more central over the mast is asking it to work less hard as a lifting surface? Whatever, will continue to experiment...
Title: Re: Getting ejected out the front door...
Post by: WingTime on October 30, 2021, 07:15:39 PM
Lots of good discussions here, thanks to all,
I have used a nano coating on my aluminum mast , I can tell the difference but have to reapply
Today I had the 999 on a cedrus project mast , lighter than most carbon masted and I really like the feel. As for mast ventilation, Iím not sure if itís better or worst will be paying more attention to this in my next session.
Title: Re: Getting ejected out the front door...
Post by: dns on October 31, 2021, 10:06:40 AM

I have used a nano coating on my aluminum mast , I can tell the difference but have to reapply


FWIW I was just working with a guy that's super into kite foil racing. He said they're all going to super polishing their masts and wings (2000-3000 grit) then roughing up the first third or so with 600 grit. Then cleaning with Windex before a race.
Title: Re: Getting ejected out the front door...
Post by: SUPeter on November 02, 2021, 08:43:41 AM
Got the 999 up to 20 mph using a 19mm(90cm) mast on multiple occasions and ventilated the mast only  a couple times so far.  That is extraordinarily good performance from my standpoint having only used homemade masts.  The ventilations are also shorter lived events which are usually recoverable as soon as the edge of the board drops to the surface I pop right back up and keep on pushing.  Having the mast at such high angles makes it much like a wing in that at certain times there will be positive pressure on one side and negative pressure on the other.  Add to this a constant access to the waters surface and voila, air is sucked down to the business end.
Title: Re: Getting ejected out the front door...
Post by: PonoBill on November 02, 2021, 11:47:40 AM
yup. I think the amount of yaw in your ride makes a difference too. Most people complaining about ventilation experience it going hard upwind, when the mast is acting like a wing with one tip out of the water. The symmetrical shape minimizes the differential pressure across the mast until you add a bit of yaw, which results in an increase in AOA with the upper surface of the mast getting more separated flow. I notice that people riding with front and back footstraps can hold a tighter reach than those who ride strapless. They might be just better foilers, but they also might be cranking in a bit more yaw and gaining lift, like a cranked over sailboat gets from its keel when the skipper adds a little yaw with the rudder.
Title: Re: Getting ejected out the front door...
Post by: Alysum on November 02, 2021, 08:10:18 PM
I'm glad I found this topic and that it's not just me experiencing regular "spin outs" on my Axis foils.

There is a long discussion on Facebook: https://www.facebook.com/groups/axisfoilriders/posts/553983515699944

Yesterday I went kitefoiling on my carbon 86 with ultrashort and 700/380 wings. Water was quite choppy.
In 2h I ventilated a total of 10 times with 7 of those resulting into a spin out and heavy crash  :-[

I also experience spin outs when winging but it seems to be less frequent than under a kite. Happened using my 830 and 999 wings too.

It doesn't happen just at high speeds, it's happened to me a low speeds as well. One possible way to explain this is the foil being more under water where the tapered carbon mast is thicker...

Ventilation is reduced with a thinner and stiff mast plus long chord according to Kyle@Cedrus.

I wouldn't exclude that it's the foils design rather than the mast design. I ride the 380 stab 90% of the time so I wouldn't exclude the winglets having a play in this. I do recall a spin out but less severe, using the progressive 400 stab.

The mystery continues....
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on November 03, 2021, 01:36:10 AM
There is a long discussion on Facebook: https://www.facebook.com/groups/axisfoilriders/posts/553983515699944

Thanks for that link - loads of good info there. Food for thought!

Currently pondering one of two options - trying the 16mm Axis mast or get my (currently cracked) Gong carbon mast that I know doesn't suffer from ventilation as far as I know mended and modified to accept the Axis fuse...
Title: Re: Getting ejected out the front door...
Post by: Alysum on November 08, 2021, 01:54:54 AM
Another long post on FB on the same issue https://www.facebook.com/groups/axisfoilriders/permalink/565139107917718/
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on November 08, 2021, 03:48:33 AM
Glad it's not just my clumsy riding then, although the real reason is still unappealing - a design issue.
My Gong carbon mast is at my local boat builder/repairer getting modified this week hopefully. Just in time for a week of high pressure and little wind...
Title: Re: Getting ejected out the front door...
Post by: Califoilia on November 08, 2021, 10:24:28 AM
Another long post on FB on the same issue https://www.facebook.com/groups/axisfoilriders/permalink/565139107917718/
I'm not on Facebook, and wondering if you can get a screen shot of a couple of the post there wrt the issue if possible. TIA
Title: Re: Getting ejected out the front door...
Post by: Alysum on November 09, 2021, 02:10:53 AM
And another one! This time with some pictures https://www.facebook.com/groups/axisfoilriders/permalink/565819407849688/
Title: Re: Getting ejected out the front door...
Post by: Beasho on November 09, 2021, 06:27:09 AM
Is what we are talking about good ole' fashion windsurfing

SPIN OUT

Those of us with a windsurfing background know Spin Out to be a function of going fast and loading up a fin on a choppy, or aerated, surface. 

We have been fighting it for decades. 
Title: Re: Getting ejected out the front door...
Post by: Dwight (DW) on November 09, 2021, 06:42:50 AM
Is what we are talking about good ole' fashion windsurfing

SPIN OUT

Those of us with a windsurfing background know Spin Out to be a function of going fast and loading up a fin on a choppy, or aerated, surface. 

We have been fighting it for decades.

Thatís my guess too. Pushing sideways instead of leaning the board over and maintaining all forces straight down the mast. Easy to make this mistake riding toe side.
Title: Re: Getting ejected out the front door...
Post by: Alysum on November 09, 2021, 12:41:46 PM
Is what we are talking about good ole' fashion windsurfing

SPIN OUT

Those of us with a windsurfing background know Spin Out to be a function of going fast and loading up a fin on a choppy, or aerated, surface. 

We have been fighting it for decades.
It happens to me a low speeds too. Many think it's because of the higher speeds we're getting with the new foils but it's not.
I once just water started and 2 secs later it ventilated at low speed.
Title: Re: Getting ejected out the front door...
Post by: Dwight (DW) on November 09, 2021, 01:46:23 PM
Windsurf fins spin out at low speed too. Donít push sideways and see if this helps.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on November 09, 2021, 01:52:46 PM
Is what we are talking about good ole' fashion windsurfing

SPIN OUT


Sort of... It is ventilation, but instead of the fin releasing downwind, this is the mast releasing upwind with a roll to windward as a minimum, and taking air down to the stab with catastrophic loss of lift at its worst.
Title: Re: Getting ejected out the front door...
Post by: Dwight (DW) on November 09, 2021, 03:25:27 PM
When I think about all the wingers with poor body form, I have to wonder if this is not the issue.

Bending at the waist. Getting themselves in such poor position the wing is pulling them one way and they are pushing back the opposite way with their feet.

Everyone should aspire to copy Johnny Heinekenís body form.

Title: Re: Getting ejected out the front door...
Post by: PonoBill on November 09, 2021, 03:40:20 PM
Is what we are talking about good ole' fashion windsurfing

SPIN OUT

Those of us with a windsurfing background know Spin Out to be a function of going fast and loading up a fin on a choppy, or aerated, surface. 

We have been fighting it for decades.
Yes and no. Spinout has numerous components, including ventilation. Ventilation means an airfoil that pierces the surface has enough differential pressure to pull air down the edge of the foil--in this case, the foil is the mast. When the air envelopes the stabilizer it's game over. A windsurfing fin generally has the bottom of the board to insulate it from the surface. If you bounce clear of the surface in chop the fin can ventilate and spin out. Most of the time though it's mostly the sideways vector of the wind and foot force that overcomes the fin's lift and it slips. Once it starts slipping and going sideways it's tough to regain control because there's no flow across the airfoil to generate lift. Likewise, landing from a jump covers the bottom of the board and the fin with air. Differential pressure from the residual forward speed keeps the air in place until there is enough flow across the fin. In that case there is virtually no lift from the fin and you have to straighten up long enough for the air to bleed off before the fin starts working. I spent a stupid amount of time measuring side thrust on fins, developing and throwing away fences and other devices to minimize ventilation. I settled on canard or slotted fins, which won't help at all with foils.
Title: Re: Getting ejected out the front door...
Post by: jondrums on November 09, 2021, 04:16:40 PM
canard mast???  hmm, got me thinking about this
I thought I put all this behind me when I gave up windsurfing all those years ago
Title: Re: Getting ejected out the front door...
Post by: PonoBill on November 09, 2021, 07:10:56 PM
I suspect that cleaning up the aluminum masts will go a long way to fixing this. I'd start with sanding off the logo and filling the dip with bondo and sanding it all super smooth--I'd probably paint the whole thing to seal the bondo and finish with 600 grit. then polish and wax. That's the cheapest way to move the needle higher.

I don't have the problem often, so I'm not that motivated to solve it.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on November 09, 2021, 10:39:37 PM
When I think about all the wingers with poor body form, I have to wonder if this is not the issue.

Bending at the waist. Getting themselves in such poor position the wing is pulling them one way and they are pushing back the opposite way with their feet.

Everyone should aspire to copy Johnny Heinekenís body form.

There could well be individual circumstances that make it worse, but that wouldn't explain the brand specific nature of my issue. Complaints on the Axis FB page seem to come from fairly experienced riders too, who also say the Axis mast is way more sensitive to it..
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on November 10, 2021, 12:44:19 AM
https://youtu.be/2tIQlDJ-XPY (https://youtu.be/2tIQlDJ-XPY)

This was submitted as an example of the issue by an experienced rider... Watch the wake of the foil closely and you'll see the sideways movement of the mast just before the incidents...
Title: Re: Getting ejected out the front door...
Post by: Fishman on November 10, 2021, 10:53:51 AM
https://youtu.be/2tIQlDJ-XPY (https://youtu.be/2tIQlDJ-XPY)

This was submitted as an example of the issue by an experienced rider... Watch the wake of the foil closely and you'll see the sideways movement of the mast just before the incidents...
I don't know which mast you use (or it's profile) but I wonder if you have experienced this with the Gong V2 aluminium mast?

 The newer V2 has a greater teardrop profile and I was curious as to why they changed from the old more symmetrical shape like the V1 and Axis mast have. After reading this I thinking this could be the answer

I would think the more teardrop shape would be less likely to aerate/ventilate if that is really what's happening.

 
Title: Re: Getting ejected out the front door...
Post by: PonoBill on November 10, 2021, 01:10:32 PM
There could well be individual circumstances that make it worse, but that wouldn't explain the brand specific nature of my issue. Complaints on the Axis FB page seem to come from fairly experienced riders too, who also say the Axis mast is way more sensitive to it..

Of course it is, who else makes a 19mm mast? There's a tradeoff between strength/rigidity and the downsides of a thicker, wider mast--drag, weight, and ventilation.

Looking at the yaw angle of the board and how far he was hiked out, I'm not surprised the mast ventilated.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on November 10, 2021, 03:15:44 PM
There could well be individual circumstances that make it worse, but that wouldn't explain the brand specific nature of my issue. Complaints on the Axis FB page seem to come from fairly experienced riders too, who also say the Axis mast is way more sensitive to it..

Of course it is, who else makes a 19mm mast? There's a tradeoff between strength/rigidity and the downsides of a thicker, wider mast--drag, weight, and ventilation.

Looking at the yaw angle of the board and how far he was hiked out, I'm not surprised the mast ventilated.

So you agree this is more of a design issue rather than a technique issue? DW was suggesting otherwise, which is what my comment was responding to.

I'm in the design issue camp, but with the caveat that individual circumstances can make it worse. Rider weight seems to be cropping up as one possibility (from FB comments), lighter riders being more susceptible, but there's no hard evidence yet...

Fishman - I do have a Gong V2 mast but only recently got it and only used it with my big foil. I will try it with my Fluid LS this weekend and see how it behaves... I normally use one of the older thinner Naish masts (similar to the Gong V1) which fits my modified Gong fuse with the LS, after my Gong carbon mast started cracking after jumping it. It's that carbon mast that's currently getting modified to fit the Axis fuse...
Title: Re: Getting ejected out the front door...
Post by: PonoBill on November 10, 2021, 05:13:44 PM
I'm certain it's a design issue, an intractable one. There are things you can do to mitigate it, but it's a fundamental element of pushing an airfoil that pierces the surface through the water. Every mast will do this under the right conditions. Skinnier masts, like the raft of 15mm ones that most companies use for an aluminum mast, will push the initiating conditions further.

I'd rather have a rigid mast that works in most of the circumstances I use it for than a floppy one that eliminates a condition I rarely encounter. But that's me.
Title: Re: Getting ejected out the front door...
Post by: JohnnyTsunami on November 10, 2021, 07:24:36 PM
Happens to me on my art 999 and 420 tail wing (tail sanded a lot on the trailing edge and half a winglet broke off) with the 86cm carbon mast.
Iím 77kg.

Iíll try and wing with more and less yaw. Iím mostly going upwind to the max so I can ride downwind.

As a beginner I would ride flat and try and yaw my way upwind. Now I ride more canted over. Front foot straps. I feel with a back foot strap it might change my yaw amount, but I prefer to ride without one unless Iím jumping.

Iíd love to know a solution.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on November 11, 2021, 01:20:55 AM
I'd rather have a rigid mast that works in most of the circumstances I use it for than a floppy one that eliminates a condition I rarely encounter. But that's me.

There would be a elegant symmetry if lighter riders needed a thinner mast to reduce ventilation and don't need the stiffness vs bigger riders who need the opposite! I guess Axis might be ahead of the game by offering 2 different thicknesses then!

I wonder if lighter riders cant their masts to windward more than bigger riders making their situation worse?
Title: Re: Getting ejected out the front door...
Post by: Dwight (DW) on November 11, 2021, 03:34:08 AM


Iíll try and wing with more and less yaw. Iím mostly going upwind to the max so I can ride downwind.



Never yaw the board. Bank angle is the correct way to drive upwind.
Title: Re: Getting ejected out the front door...
Post by: JohnnyTsunami on November 11, 2021, 03:12:21 PM
I just had a session and was thinking about this. I find when I put my rear foot further back and more center where my rear strap would be (itís usually a bit on the downwind side of the board and more forward) I lean over more and yaw less.

Makes me wonder if this is the reason kitefoil racers have a RIDICULOUSLY wide stance - to be in a better position for optimizing upwind and preventing mast ventilation? Makes sense that wingers would have this problem with our relatively slow speed we have our feet closer together and get away with it unless weíre hauling ass upwind.

Just a bunch of guessesÖ
Title: Re: Getting ejected out the front door...
Post by: PonoBill on November 11, 2021, 06:32:03 PM
Probably a pretty good guess. Adding yaw increases lift in the upwind direction by increasing the angle of attack (good!) but that lift is generated by differential pressure across the foil (bad!) which is something we can get away with when our wing is fully submerged, but turning a surface-piercing mast into a wing by increasing the angle of attack does the same thing as popping a wingtip out of the water.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on November 28, 2021, 11:43:55 AM
Just to update the thread, I've finally had a couple of sessions on the modified Gong mast with the 999 and it's all good! The repeated ventilation has gone, which is a massive relief -  can get back to focusing on getting upwind as hard as possible.

What this whole experience ha done is made me more aware of the issue, and actually the Gong mast did ventilate a handful of times, but only when hit by a large white cap in big winds, right on the sweet spot which would be difficult for anything to handle, and if on flat water, it would begin to ventilate, but it just quickly sorted itself out without any action from me. I probably didn't notice it when I used that mast in the past...

The new setup is 500g lighter than the Axis mast, which is noticeable lighter, even just carrying my kit to the water. Stiffness wise it's difficult to judge because I'm now using the 375P tail rather than the 380, which way looser, and much more to my liking. I've even ordered the 350 now there's more to squeeze out of the 999 as a windy setup... Looking forward to giving that a go, but it's getting cold in the UK now, which always makes me feel like a kook again...
Title: Re: Getting ejected out the front door...
Post by: PonoBill on November 28, 2021, 07:22:16 PM
cool, I've had a somewhat square rubber band on my mast for a while to defang ventilation. I didn't have an issue before, and I'm not having it now, so it's working--at least as well as a SharkBanz does. Are those guys still around and not in jail?
Title: Re: Getting ejected out the front door...
Post by: Alysum on December 01, 2021, 05:27:23 AM
Just to update the thread, I've finally had a couple of sessions on the modified Gong mast with the 999 and it's all good! The repeated ventilation has gone, which is a massive relief -  can get back to focusing on getting upwind as hard as possible.

What this whole experience ha done is made me more aware of the issue, and actually the Gong mast did ventilate a handful of times, but only when hit by a large white cap in big winds, right on the sweet spot which would be difficult for anything to handle, and if on flat water, it would begin to ventilate, but it just quickly sorted itself out without any action from me. I probably didn't notice it when I used that mast in the past...

The new setup is 500g lighter than the Axis mast, which is noticeable lighter, even just carrying my kit to the water. Stiffness wise it's difficult to judge because I'm now using the 375P tail rather than the 380, which way looser, and much more to my liking. I've even ordered the 350 now there's more to squeeze out of the 999 as a windy setup... Looking forward to giving that a go, but it's getting cold in the UK now, which always makes me feel like a kook again...

Thanks for the update, how thick is the gong mast.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on December 01, 2021, 09:36:51 AM
Thanks for the update, how thick is the gong mast.

Good question! Just measured at the point the mast was shortened, and it was 14.5mm across the cut. Obviously tapers to more closer to the plate, but difficult to measure accurately there as my calipers don't quite reach to the widest point but probably around 16-17mm.

Certainly suggests that thinner is better from a ventilation perspective...
Title: Re: Getting ejected out the front door...
Post by: Alysum on December 01, 2021, 02:34:56 PM
Well the axis carbon is 14mm at the bottom... Unless most of my ventilation happens further up the mast.

Hopefully the Axis v3 carbon mast fixes the issue, whenever that comes out.
Title: Re: Getting ejected out the front door...
Post by: surfcowboy on December 06, 2021, 09:03:42 PM
https://youtu.be/mLFU7fQWXQs

Dig that. At the end he says he doesn't recommend sanding aluminum masts but who wants to try with a little matte clear poly or other matte paint?

Axis is anodized. Gong is painted and not glossy.

Windsurfers, who knew they knew stuff? 😉
Title: Re: Getting ejected out the front door...
Post by: Alysum on December 07, 2021, 04:19:42 AM
Very interesting... And it's ventilation he experienced (not cavitation). So who's sanding down their axis carbon mast  ;D
Title: Re: Getting ejected out the front door...
Post by: surfcowboy on December 07, 2021, 07:45:51 PM
Oh he says to not sand aluminum but I am wondering what Solent thinks about the painted Gong vs smooth anodized Axis.
Title: Re: Getting ejected out the front door...
Post by: Dwight (DW) on December 08, 2021, 03:45:47 AM
So who's sanding down their axis carbon mast  ;D

Evan sands all his. Mine is sanded now.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on December 08, 2021, 01:58:51 PM
Oh he says to not sand aluminum but I am wondering what Solent thinks about the painted Gong vs smooth anodized Axis.

Tough one... The finish on the Gong mast is more a satin clear coat and could probably do with a refinish so is hardly special. I've been using an old Naish aluminium mast a lot too which is more a matt finish and didn't have any ventilation issues. All three masts are very different shapes so isolating the factors that might contribute to ventilation is difficult.

Having said that, I would be astonished if sanding fixed the Axis mast. It's so far away from giving me acceptable ventilation performance that I'm struggling to believe that a bit more turbulent flow over that section shape would make a significant difference at the speeds I'm operating at. At the higher speed of wind foil racing, I could see that making a difference, but I'm speculating really...

I've heard so much pseudo science on roughed finishes that I'm sceptical of believing anything I haven't tried for myself. Not saying it doesn't work, but that the application is quite specific.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on December 12, 2021, 11:13:23 AM
Fishman - I do have a Gong V2 mast but only recently got it and only used it with my big foil. I will try it with my Fluid LS this weekend and see how it behaves... I normally use one of the older thinner Naish masts (similar to the Gong V1) which fits my modified Gong fuse with the LS...

Took out the Gong V2 aluminium mast today with the LS and it was just as bad as the Axis aluminium mast for ventilation. Pretty disappointed really. It'll be fine with the big XXL-S, but I won't use it with the LS again. It has a very different profile to the Axis - more teardrop, but 2mm thinner, so 17mm so had high hopes it would be fine for me. Finish is not as shiny as the Axis. I'll have to stick with the Naish for the foreseeable or get a V2 Gong carbon mast...
Title: Re: Getting ejected out the front door...
Post by: Fishman on December 13, 2021, 07:04:47 AM
This thread turned out to be more helpful than I realized.
A couple of weeks ago I switched up some foil gear. At one point I found myself repeatedly falling right after getting on foil. I even turned the board over to examine the foil for maybe something loose but it all was tight. But I think moving the foil toward might have helped a little also.

I mainly use a X-Over stab, 85cm mast and a Gong curve XLT. That time I switched to L Fluid stab, curve LT and A 95cm mast when this falling was happening. My solution at the time was to go a good bit further down wind before cutting upwind and not turning as hard. In hindsight I think this ventilating issue was what was really happening. I think the flatter stab was letting me Yaw were the X- Over stab with its vertical tips... would have minimized my Yaw.
 Now that I have the Yaw factor in mind it should help me get a little better at foiling :)

Hey Christian do you have any photos of your mast's-es-s mods?
Title: Re: Getting ejected out the front door...
Post by: Alysum on January 23, 2022, 07:47:24 PM
Lots of talk about mast ventilation in Hadou's latest video:

https://www.youtube.com/watch?v=7MdOrrQykNM
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on January 24, 2022, 01:55:03 AM
Was stoked to hear the Cedrus mast sn't overly sensitive to ventilation. I had been in touch with Kyle about mast ventilation, but as it seems a rider specific issue there was no guarantee that the Cedrus would be the solution. Seems that it is one, so that is great!
Title: Re: Getting ejected out the front door...
Post by: supmmmm on January 24, 2022, 08:52:14 AM
cool, I've had a somewhat square rubber band on my mast for a while to defang ventilation. I didn't have an issue before, and I'm not having it now, so it's working--at least as well as a SharkBanz does. Are those guys still around and not in jail?
Can you pls share more details on this - placement of band on mast and type of rubber band used - Iím thinking the ones they use to group broccoli together at the grocery store- or thicker?
Title: Re: Getting ejected out the front door...
Post by: PonoBill on January 24, 2022, 10:10:49 AM
A broccoli band would probably be fine. I cut mine from a thick rubber band I had kicking around the shop. It's on my 90CM Axis carbon mast, and I didn't bring that to Maui. I really don't have a consistent issue with the Axis aluminum mast. I have done the "fall out of the sky" thing a few times with the 999 and 400/60 but it's rare. I don't know that the band does a thing, but I'm sure about Shark Banz. They don't do anything more than a little shark chant would do. At least the broccoli band doesn't cost 94 bucks.
Title: Re: Getting ejected out the front door...
Post by: PonoBill on January 24, 2022, 10:36:05 AM
It's good to hear the Cedrus mast works so well. I'm probably going to get one sooner or later, not because of ventilation but for rigidity. the old Axis carbon mast I have feels like a noodle with bigger wings and my fat ass pounding on it. the Axis 19mm aluminum makes all that go away, and it's a hundred bucks, but I like the idea of an equally rigid carbon mast. The way the Cedrus is made the leading and trailing edges can be shaped independently of the load-bearing structure of the mast. I'm a believer in this way of making masts, and wings too for that matter, though no one will probably ever do that.
Title: Re: Getting ejected out the front door...
Post by: Mike dubs on January 24, 2022, 10:47:46 AM
It's a great mast, I have one. If you're jumping or heavy then get the Clydesdale  version. Pono, where do u place the rubber band?
Mike
Title: Re: Getting ejected out the front door...
Post by: supmmmm on January 24, 2022, 12:36:38 PM
A broccoli band would probably be fine. I cut mine from a thick rubber band I had kicking around the shop. It's on my 90CM Axis carbon mast, and I didn't bring that to Maui. I really don't have a consistent issue with the Axis aluminum mast. I have done the "fall out of the sky" thing a few times with the 999 and 400/60 but it's rare. I don't know that the band does a thing, but I'm sure about Shark Banz. They don't do anything more than a little shark chant would do. At least the broccoli band doesn't cost 94 bucks.

Thanks - will try that out on my alum mast. At this point Iím not sure if itís my technique, equipment (also using PNG 1300 and 910ís) up front but I had some pretty spectacular bails out the front during my month south in the Dominican. My friends have commented that my stance is somewhat narrow (i bring that over from my snowboarding and sup surfing)
I did pickup a tip that Iíve yet to try - was listening to Roberts interview with Mark Rapphorst and he mentioned that he micro shims the front of his stabs with slices of beer cans - he didnít mention the issue that all are trying to solve here but I wonder if itís related. Canít recall how they got into the shimming topic.
Be well - jaime
Title: Re: Getting ejected out the front door...
Post by: PonoBill on January 24, 2022, 06:00:13 PM
I find the 1300 does some really strange stalls. I've never warmed up to it. It's in my van but it's almost virgin. Some of the really good foilers here on Maui do magic with it, but for me, it's a crash waiting to happen.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on January 25, 2022, 09:19:48 AM
Mast ventilation cropped up on the Gong FB group today. Their V2 Alu mast ventilates more than the Axis for me. Patrice basically said 'don't blame your tools', it's well tested, and has been used to a very high level.

Out of respect for him and his advice I'll try again to work out my issue with it, but it was pretty bad last time I used it... Even trying to nurse it along, it still chucked me off way too regularly... We'll see! Finally got some wind coming. Been a 3 week wind drought here...
Title: Re: Getting ejected out the front door...
Post by: JohnnyTsunami on January 25, 2022, 09:50:44 AM
I have had success stopping ventilation by leaning more and yawing less as a result of this thread. My mast ventilations basically stopped, but I haven't been foiling much lately due to NO WIND  >:(.

I assumed it was my carbon mast because it is tapered and angled to bring any ventilation downwards (what happened to reverse angled masts?), but hearing it's on the aluminum mast which is machine produced and a perfectly straight foil makes it so that I have NO idea what causes it, just that putting less pressure on the mast foil by yawing less helps a ton.

It hasn't happened on my mike's lab foil which I drive quite hard and fast.

Mike's Lab says this:

"Ventilation on the strut can happen for a variety of reasons. Most often ventilation occurs due to impurities that can build up on the leading edge, or scratches that can result from hitting things in the water. Water temperature and sea state also play an important role in the separation of laminar flow on the strut.

It is very important to keep the strut very clean, especially the leading edge. Do not touch it with dirty or greasy hands. You can clean the mast periodically with alcohol or household glass cleaner.

If you have persistent ventilation problems, or some surface defects and leading edge scratches as a result of hitting something in the water, please use the following procedure to bring back the leading edge to original performance:

You should do this only if you feel absolutely confident, otherwise you may risk changing the profile of the leading edge. If in doubt please contact us"


... followed by instructions on how to fair and sand a mast. 
Title: Re: Getting ejected out the front door...
Post by: PonoBill on January 25, 2022, 10:25:53 AM
There are two technique factors that influence ventilation: yaw and trim. Yaw is fundamentally twisting the mast relative to its motion through the water. When the whole assembly is leaned well over the mast is essentially a wing with a symmetric foil. Yaw (twisting the mast) changes the angle of attack of the mast and creates lift (differential pressure) along its submerged length. At higher speeds and greater lean angles, any yaw will draw air from the surface. If the air column gets close to the wing the high differential pressure on the top of the wing overcomes the shortened water barrier keeping air from reaching the wing, and boom, air surrounds the wing and reduces the lift by a factor of about 1000. And boom, down you go. So yeah, yaw is bad.

Trim is important too because it affects the angle of attack of the wing. You're zooming along, leaned over, and your board starts trimming nose high. Naturally, at higher speed, you try to keep the board trimmed flat. Unfortunately, you're human, with relatively huge delays built into your pathetically slow computer and communication and control system, so you lag and overcontrol, which pitches the board down, so you lighten your front foot pressure a tiny bit and bob along, doing the worst thing you can possibly do while going fast. The cycle repeats and each time it does you are varying the lift of the wing, pulsing the differential pressure to too low, then too high, then too low. Not only are you varying the depth of the wing in the water, and therefore the length of the water column separating the wing from the air, you're also probably changing your yaw angle too. Smooth is good.

The easiest way to trim is shimming the stabilizer to give you a ride at a high speed that doesn't require constant adjustment of foot pressure. The faster you go, the more front foot pressure is required to overcome the stabilizer changing the angle of attack of the front wing. You can't bring the stabilizer to a neutral position because that is inherently unstable, but you don't need the four or five degrees of incidence angle that your rear wing has dialed into it. That might work very well at 10 mph, but the upward force is going to increase by the square of the speed difference. You probably don't feel that if you're good enough to go fast in control, but a big BIG part of being "good enough" is committing that control to muscle memory. You don't feel the difference any more than you feel the greater steering force required to turn your bicycle at 25 mph vs. 24 mph, but you'd have to know nothing about gyroscopes to not know it's there.

The first thing I'd try if I were having problems with ventilation is trimming my stabilizer. But that's me. Reducing the incidence angle reduces the forces you need to apply to the front foot to stay trimmed, and reduces the muscle-memory-controlled pitch cycles. Sooner or later the ventilation will come back. If you go faster, lean out further, you'll eventually reach a speed that ventilates the wing. You can learn not to yaw and push that a little higher, but then you'll go faster and it will come back.

If the billions spent on AC and other race boats can't eliminate the problem, what exactly can you expect from a hundred buck mast? Patrice is right.

Title: Re: Getting ejected out the front door...
Post by: tarquin on January 25, 2022, 11:03:02 AM
Yes at the end of the day asking 1 mast to work in different conditions with different riders just ain't going to happen. There are too many variables.
 I know guys that do IMOCA boats and a guy on the INEOs build team. He worked on Hugo Boss before that. They work so hard to keep everything within "the parameters". Asking 1 mast to work for different wings, foils, riders weight and technique, board weight, water temp, salinity of the water ,AOA etc is asking a little much .
 There are plenty of studies on stopping ventilation. Most of them dont work in the real world. Fences as Ponobill mentioned work in perfect conditions.
 One of the reasons IMOCA foils are so big is to allow for a large percentage of it NOT working because of variables.
 Top comment from a guy who knows his stuff after a few beers was something like " i can't believe it actually works".
Title: Re: Getting ejected out the front door...
Post by: PonoBill on January 25, 2022, 12:16:28 PM
I can't believe wing foiling or SUP foiling works. I only understand the basics of foils, but the simple fact that lift increases as the square of the speed and the only control we have is weight shift seems to make the entire notion unworkable. But it does, and it's fun.

I know some of the more sophisticated applications run the foils with ventilation as part of the way they operate. That seems incredible, but it's probably the only way other than deeply laddering the foils or running them on the surface that permits operation beyond otherwise limiting speed. And at some point cavitation starts. That's far more difficult to deal with and it causes damage even to specially alloyed metals that resist the surface erosion.
Title: Re: Getting ejected out the front door...
Post by: supmmmm on January 25, 2022, 01:01:27 PM
I gotta ask - this ventilation issue - I assume itís become more evident as people move to faster higher aspect wings? I know plenty of people that came up on axis gear (letís call it with low aspect wings) who didnít experience this issue before - or am I missing something?
Title: Re: Getting ejected out the front door...
Post by: tarquin on January 25, 2022, 01:35:06 PM
Yes. So many people fought cavitation. Who broke the speed sailing record by inducing cavitation with a wedge shaped foil. The Perigrine falcon is the fastest bird in the world. WHY ??
Multiple ladders just don't work in the real world.
 As far as surface erosion most of the offshore cats suffered massively from this. They couldn't understand why the foils failed all of a sudden. The last cup boats where having to do massive work to the leading edge after each race.
 Sorry after numerous beers no answers.
 Its no secret but most high speed and offshore foils are a mixture of metal(still don't know) leading and trailng edge, airex core inbetween. Then prepeg carbon. Baked in an autoclave. Sometimes over days. Every little thing is calculated. INEOs bought out the epoxy they found to be best. Not the brand just the type that company made so the others couldn't use it. Same with the carbon fibers. Just to give them an advantage!!!!
 We are where we were I don't know 30 years ago. The cycle will start again.
Title: Re: Getting ejected out the front door...
Post by: PonoBill on January 25, 2022, 08:12:08 PM
I gotta ask - this ventilation issue - I assume itís become more evident as people move to faster higher aspect wings? I know plenty of people that came up on axis gear (letís call it with low aspect wings) who didnít experience this issue before - or am I missing something?

Mostly just progression I think. If you're on low aspect wings you probably won't reach speeds where ventilation is inevitable. Some people probably did go faster and crashed and didn't know what to call it. You'll probably never ventilate in a wave, for the most part, you're not hiking out or yawing.

Any old windsurfer recognizes this cycle. For a long time, people were trying to make fins that overcame "cavitation" which was actually ventilation. Really fast windsurfers contact the surface of the water with a few square inches of board and fins that barely work even in a straight line--they are ventilating constantly. They don't turn until they slow down, which happens very quickly when they aren't applying full sail power. Then it was the kiters suffering, though they generally get to go faster before the wheels fall off the bus. Kiting is an aerial sport, in part because it's really hard to keep the board on the water.

Slicing something through the water at 20+ mph is a big problem, and the faster you go, the nuttier the physics gets. You are parting an incompressible medium that is a thousand times denser than air, using equipment that is about as minimal as it can be, with a control system that probably shouldn't work at all.

Crazy shit. What fun!
Title: Re: Getting ejected out the front door...
Post by: supmmmm on January 25, 2022, 08:36:13 PM
Haha - thatís great 😀🤙
Going west tmrw for a weeks trip snowboarding in Banff - will get back at this wing n foil stuff in the spring down in Hatteras. Actually picked up a surf board for the foil to play with as well.
Be well Bill - your feedback is much appreciated 🙏
Title: Re: Getting ejected out the front door...
Post by: Hdip on January 25, 2022, 09:30:40 PM
Mostly just progression I think. If you're on low aspect wings you probably won't reach speeds where ventilation is inevitable. Some people probably did go faster and crashed and didn't know what to call it. You'll probably never ventilate in a wave, for the most part, you're not hiking out or yawing.

Just to prove there is an exception to every rule. Prone foil,  low aspect surf wing, slow 1 foot waves. I sold a mast due to ventilation issues. A thinner mast has fixed the problem. Or maybe, it's a mast that has flex that has fixed the problem. Who knows.
Title: Re: Getting ejected out the front door...
Post by: supmmmm on January 25, 2022, 10:35:57 PM
Mostly just progression I think. If you're on low aspect wings you probably won't reach speeds where ventilation is inevitable. Some people probably did go faster and crashed and didn't know what to call it. You'll probably never ventilate in a wave, for the most part, you're not hiking out or yawing.

Just to prove there is an exception to every rule. Prone foil,  low aspect surf wing, slow 1 foot waves. I sold a mast due to ventilation issues. A thinner mast has fixed the problem. Or maybe, it's a mast that has flex that has fixed the problem. Who knows.

Would you mind sharing which mast you sold and what you went with instead for prone foiling?
I was thinking of maybe getting the 16mm axis mast for prone foiling.
Title: Re: Getting ejected out the front door...
Post by: tarquin on January 26, 2022, 12:47:12 AM
Really interesting interview and loads of info about IMOCA foils and the different approaches. To give you an idea of how complicated it gets.
https://youtu.be/3OaUEJG2RnE
Title: Re: Getting ejected out the front door...
Post by: Hdip on January 26, 2022, 08:56:08 AM

Would you mind sharing which mast you sold and what you went with instead for prone foiling?
I was thinking of maybe getting the 16mm axis mast for prone foiling.

When I was on full axis I had the 16mm mast and didn’t have the problem. I had a universal mast that was 19mm and had the ventilation problem. Since I was only on lift wings at that point and lift had come out with their current mast I just sold the universal mast and got lift. The lift is 14mm thick I believe.

Since I’m the only one of at least 5 guys down here that had the issue I don’t feel it’s fair to publicly name the universal mast. Like I said though. Exceptions to every rule. It really makes me think it’s a stiffness issue that’s the problem. To stiff can be bad in my mind.

The problem would repeatedly occur when dropping into a slow wave and trying to bottom turn, twist and drive to gain speed. So as ponobill said. Hiked over and yawing at the same time.
Title: Re: Getting ejected out the front door...
Post by: PonoBill on January 26, 2022, 10:25:55 AM
Yeah, I should probably have stated an exception for prone foilers, and Junya, Dave and Austin on SUP foils. I see the torque and lean angles these folks employ every time I surf foil. That's the outer edge of possible and probably a foot beyond the line.
Title: Re: Getting ejected out the front door...
Post by: Velasco on January 26, 2022, 11:35:32 PM
I think I am the guy that bought Hdip's 75cm universal mast.  I have proned foiled it in everything from knee high waves to well overhead (Takuma Kujira 1210/self made 14.75" G10 rear stab).  I'm 185# and I've never ventilated this mast.  In fact, I've gotten 5 for 1s, and cranked the hardest leaned out turns all on the same rides - so this mast has served me well.  I've also used it winging (but not much as it is a hair shorter than my preference for winging)- and I have not ventilated it at speed either.

I liked this mast so much I bought an 85cm version (and I'm waiting for a 68cm to prone during lower tides).  I have ventilated while using the 85 (with the ART999/420 on the Ultrashort fuselage) - but that was going faster than 25mph.  I need to use the Kujira on both the stock aluminum 85cm mast (I had to buy this to get the fuselage) and this universal and see if it is rider error or truly a thickness difference.  I haven't experienced ventilation on the stock mast - but then again I haven't used the Kujira on the universal yet.

So to convolute this topic even more - same mast cross-section, different uses, different results
Title: Re: Getting ejected out the front door...
Post by: tarquin on January 27, 2022, 12:42:08 AM
https://youtu.be/NefnpuxS2uM
 Had a talk with a friend that has done some IMOCA stuff. He said ventilation is normally caused down low by some sort of disturbance. Which is part of the reason for winglets,curved wing tips. What ever you want to call them.
 He doesn't foil and the foils that they use are different. But he had a quick look and thought this.
  Maybe its not the mast but a vortex being created by the fuse mast join or somewhere else. This would partly explain the different experiences from people. Same mast but different fuse/ foil setup. He said if you look at moth foils and the last Americas cup foils they have the central torpedo. This is to help prevent ventilation. Anywhere you have a join is a problem spot that could start a vortex and lead to ventilation.
 
Title: Re: Getting ejected out the front door...
Post by: tarquin on January 27, 2022, 05:02:22 AM
These guys were great during the last AC explaining things.
https://youtu.be/x_CzbAvQaZE
Title: Re: Getting ejected out the front door...
Post by: Hdip on January 27, 2022, 07:03:37 AM
I think I am the guy that bought Hdip's 75cm universal mast.

Yeah! I figured I was the problem here. Glad youíre stoked on it.
Title: Re: Getting ejected out the front door...
Post by: Fishman on January 29, 2022, 11:14:40 AM
https://youtu.be/mLFU7fQWXQs

Dig that. At the end he says he doesn't recommend sanding aluminum masts but who wants to try with a little matte clear poly or other matte paint?

Axis is anodized. Gong is painted and not glossy.

Windsurfers, who knew they knew stuff? 😉
This makes the most sense to me as a contributing factor, when we accidently introduce more low pressure on one side of the mast. How much of a factor... maybe more than we would think???
Waxes, nano coating, oils from you hands and uber smooth surfaces all push water away. Replaced by air, so yeah.
 Not sure of any other reason to not have the same rule to "aluminum" masts.  I suspect the only reason he may have not recommended sanding for aluminum mast, is  maybe for concerns of removal of the  protective anodized coating on most brands.

The paint coating on the Gong v2 aluminium mast even thought it's "textured", it is very hydrophobic. Even after sanding one of mine it remained hydrophobic until I got all the texture removed. The paints so thick it might be better to strip it chemically, then paint it, then sand. I'm only sanding my 95cm for now.

The parallel sides of the universal masts are plain ole not going to have as much low pressure at the same mast angle as the more hydro dynamic shape (except for the trailing edge which less likely to cause any control problem. Just maybe more drag which probably wouldn't matter for most of us.
Title: Re: Getting ejected out the front door...
Post by: clay on February 12, 2022, 05:07:48 PM
Bumping this thread to see if there is any new info?

I did quick test a while back on a new faster wing in lighter wind and ventilated at speed during a gust.  Immediately gave up on these wings until I find a solution.  So my interest is not face planting so I can actually give these wings a proper go and see how they ride when winging. 

Video I have seen it's the air getting to tail and the tail losing lift that causes the blow up, so maybe adding something to the mast or fuse can divert or clear that air flow to maintain altitude?

The other times I have mast ventilated is fully loading up overpowered harnessed in driving hard upwind and the mast cutting through some chop.

Never had it happen surf foiling, I have reached around 28mph in 10 foot surf and no issues.
Title: Re: Getting ejected out the front door...
Post by: Solent Foiler on February 12, 2022, 11:40:53 PM
Half an update...

We had a bit of a wind drought during January and I didn't get out for 3 weeks, but first time back I had another go on the Gong V2 mast (which was way worse than the Axis 19mm) and made it work! 'Surprised' was an understatement!

I consciously tried to drive laterally through my back foot and not force yaw through my front foot. Whether the time off made me more sensitive to what the mast was doing, I don't know, but I am happy with the outcome. I haven't tried it again since, so not counting my chickens as conditions play a part too, but it does look like this could be a case of being user rather than equipment issue.

What I don't understand is that I really tried previously to alter my technique to work with it, but without success, so what suddenly clicked, I have no idea. This sport keeps you humble...

(EDIT to say I've not tried the Axis mast again so update on that from me)
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