Author Topic: Getting ejected out the front door...  (Read 16891 times)

Fishman

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Re: Getting ejected out the front door...
« Reply #60 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?
SupSurfMachine 9'9" longboard
SupSurfMachine  8'2" funboard

Alysum

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Re: Getting ejected out the front door...
« Reply #61 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

Solent Foiler

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Re: Getting ejected out the front door...
« Reply #62 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!
I'm 5'10", 66kg riding:
Swift Foil Boards custom 4'10 x 19.5" 35L
Gong Lethal 4'6 65L
Axis ART 799, 899, 999
Gong Fluid L-S, XXL-S on 85cm mast
Duotone Slick 3m, 4m, 5m

supmmmm

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Re: Getting ejected out the front door...
« Reply #63 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?

PonoBill

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Re: Getting ejected out the front door...
« Reply #64 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.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

PonoBill

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Re: Getting ejected out the front door...
« Reply #65 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.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Mike dubs

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Re: Getting ejected out the front door...
« Reply #66 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

supmmmm

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Re: Getting ejected out the front door...
« Reply #67 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

PonoBill

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Re: Getting ejected out the front door...
« Reply #68 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.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Solent Foiler

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Re: Getting ejected out the front door...
« Reply #69 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...
I'm 5'10", 66kg riding:
Swift Foil Boards custom 4'10 x 19.5" 35L
Gong Lethal 4'6 65L
Axis ART 799, 899, 999
Gong Fluid L-S, XXL-S on 85cm mast
Duotone Slick 3m, 4m, 5m

JohnnyTsunami

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Re: Getting ejected out the front door...
« Reply #70 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. 

PonoBill

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Re: Getting ejected out the front door...
« Reply #71 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.

« Last Edit: January 25, 2022, 10:33:14 AM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

tarquin

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Re: Getting ejected out the front door...
« Reply #72 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".

PonoBill

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Re: Getting ejected out the front door...
« Reply #73 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.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

supmmmm

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Re: Getting ejected out the front door...
« Reply #74 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?

 


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