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gorgesailor said..

This is what I am saying though. The C.O.G of the foil alone is irrelevant. You can't isolate the foil when considering C.O.G. because the foil is being driven through the mast/fuse connection. The C.O.L calculations are very interesting indeed & I think a good way to understand how stance may need to be adjusted for different foils.

The calculation doesn't produce the center of gravity. It produces a neutral point. The neutral point is the point around which all the hydrodynamic forces of the wing and the stab are balanced. The neutral point only looks at the foil. I own an I84 S48 foil and stab. I'm thinking about buying an I99 foil and the using the current 48 stab. The calculation tells me how much the neutral point is going to change.

The assumption is that the wind strength I'm sailing in, the sail size, the sail mast location, weight position, etc... all remain the same. Only the wing I'm running is different.

If the center of all the forces acting on the foil in the is behind the neutral point you will have a tough time foiling. This condition is call static instability. If all the forces are a good distance in front the neutral point you will have static stability, but the foil will be less responsive. If you have a static margin of 10% you will have both static stability and responsiveness. I'm calling that point the center of gravity with a 10% static margin.

If you take the distance from the leading edge of the wing to the neutral point, then the center of gravity with a 10% margin is 90 percent of that distance. Its a calculated value not the real center of gravity of anything. I hope this helps!

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gorgesailor said..

This is what I am saying though. The C.O.G of the foil alone is irrelevant. You can't isolate the foil when considering C.O.G. because the foil is being driven through the mast/fuse connection. The C.O.L calculations are very interesting indeed & I think a good way to understand how stance may need to be adjusted for different foils.

The calculation doesn't produce the center of gravity. It produces a neutral point. The neutral point is the point around which all the hydrodynamic forces of the wing and the stab are balanced. The neutral point only looks at the foil. I own an I84 S48 foil and stab. I'm thinking about buying an I99 foil and the using the current 48 stab. The calculation tells me how much the neutral point is going to change.

The assumption is that the wind strength I'm sailing in, the sail size, the sail mast location, weight position, etc... all remain the same. Only the wing I'm running is different.

If the center of all the forces acting on the foil in the is behind the neutral point you will have a tough time foiling. This condition is call static instability. If all the forces are a good distance in front the neutral point you will have static stability, but the foil will be less responsive. If you have a static margin of 10% you will have both static stability and responsiveness. I'm calling that point the center of gravity with a 10% static margin.

If you take the distance from the leading edge of the wing to the neutral point, then the center of gravity with a 10% margin is 90 percent of that distance. Its a calculated value not the real center of gravity of anything. I hope this helps!

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lakeeffect said..
The calculation doesn't produce the center of gravity. It produces a neutral point. The neutral point is the point around which all the hydrodynamic forces of the wing and the stab are balanced.

For that, you'd have to actually calculate the hydrodynamic forces, which would be a major undertaking. From what you've written so far, it seems that you are not doing that, but rather assume that the hydrodynamic forces generated per square centimeter are the same for front wing and stab. That's a very questionable assumption, which must be at least partially incorrect for stabs where the angle of attack can be adjusted.

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lakeeffect said..

gorgesailor said..

This is what I am saying though. The C.O.G of the foil alone is irrelevant. You can't isolate the foil when considering C.O.G. because the foil is being driven through the mast/fuse connection. The C.O.L calculations are very interesting indeed & I think a good way to understand how stance may need to be adjusted for different foils.

The calculation doesn't produce the center of gravity. It produces a neutral point. The neutral point is the point around which all the hydrodynamic forces of the wing and the stab are balanced. The neutral point only looks at the foil. I own an I84 S48 foil and stab. I'm thinking about buying an I99 foil and the using the current 48 stab. The calculation tells me how much the neutral point is going to change.

The assumption is that the wind strength I'm sailing in, the sail size, the sail mast location, weight position, etc... all remain the same. Only the wing I'm running is different.

If the center of all the forces acting on the foil in the is behind the neutral point you will have a tough time foiling. This condition is call static instability. If all the forces are a good distance in front the neutral point you will have static stability, but the foil will be less responsive. If you have a static margin of 10% you will have both static stability and responsiveness. I'm calling that point the center of gravity with a 10% static margin.

If you take the distance from the leading edge of the wing to the neutral point, then the center of gravity with a 10% margin is 90 percent of that distance. Its a calculated value not the real center of gravity of anything. I hope this helps!

Ah, yes. That makes more sense. So you are trying to calculate a center of hydrodynamic stability rather than center of gravity. This could be pretty tough as boardsurfr pointed out due to all the factors at play....

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boardsurfr said:



For that, you'd have to actually calculate the hydrodynamic forces, which would be a major undertaking. From what you've written so far, it seems that you are not doing that, but rather assume that the hydrodynamic forces generated per square centimeter are the same for front wing and stab. That's a very questionable assumption, which must be at least partially incorrect for stabs where the angle of attack can be adjusted.

Yes I agree that analyzing a foil by calculating the hydrodynamic forces would be a major undertaking and also that is not what I'm doing. In addition I agree that the hydrodynamic forces generated per square centimeter are not the same for the wing and the stab.

The stab acts in the wake of the wing and its not as efficient as the wing. I used a stab efficiency factor to cover that. Also I used a factor for the downwash of the wing which angles the flow downward over the stab. These factors are not finely tuned values. They are guess estimates.

In addition I used a factor for the difference wing and stab lift slope coefficients. In Slingshot foils the cambered side of the I84 wing is up and on the S48 stab the cambered side is down. Also when the wing is at a zero angle of attack the stab incidence angle is down. Again this factor is not a finely tuned value. It is a guess estimate.

You have to remember my purpose in is to validate with numbers for myself the experiences of CoreAS, excav8tor, and others that there is not a noticeable difference in where they stand on the board when they moved from a Slingshot I84 S48 wing/stab combination to a I99 S48 wing/stab combination. Again, I hope this helps.

PS: I'm going to buy a Slingshot I99 wing in the spring!

This is interesting work. Like most of the rest of our sport, we usually do things pretty much empirically.

We start by getting the front wing between the front and back foot, then try it out. We make small adjustments in footstraps, mast track base, sail size and type, and, if possible, foil location under the board until everything works.

Once it works, you're there. Now go out and foil your brains out.

I am a little reluctant to jump in, but thought I would share my experiences learning to windfall; which might or might not help. The first few sessions I ever had were with my Slingshot Fwing on an old GO Board, with in bound foot straps; and like most, I was able to fly and partially jibe, with a few crashes. But rarely used the rear foot straps.

Then I repurposed a 1 meter wide formula board but left off the foot straps because I could not see myself getting in them with my ability. I placed the mast as far back as I could. And quickly got very comfortable foiling and jibing. To put this in perspective I am just a retired guy that still windsurfs and plays ice hockey way more than windfoils. However reading through this these insightful posts, I think what happened to me, was rather than going through all the foot strap adjustments, on a board not build for foiling, I simply moved my feet to where I felt comfortable for the conditions or what I was doing.

Since then I have taught a few windsurfers to foil on the strapless formula board and they were quickly up and flying. I have also talked a few windfoilers to try jibing without foot straps and they quickly advanced. I have been very comfortable jibing, riding swells and just having a blast, all without straps. Kind of like many SUP and Kite foilers. And unlike my friends I have never been hurt while falling in the straps.

I now ride a custom Roberts with a Moses 101, without straps primarily under 20 knots. I have also ridden my friends boards with straps and had a blast. I would say that being able to pull up on cut backs allows you to be more aggressive on the swells but still think there is no advantage to foot straps when jibing; as I try to explain in my video, which someone posted in the jibing discussion on this great site.

Hope this helps and have fun foiling

Adrian Hessels? If so your youtube presentation is the best! I was so entertained that I have to watch it a second time for content.

I had somehow missed Adrian's jibe video, but find it quite helpful. His emphasis on the foot placement is different from other foil jibe instruction I've seen, but makes a lot of sense to me. I think it's worth posting the video again here:

I'm going to learn to foil strapless too! There are more and more videos now with people windfoiling strapless, and they look so at eas on the water.

Yes, nice comments. The obvious benefit to foiling strapless is that you can easily find the balance point without any preconceived locations on the board. This is especially nice on a formula board, where the straps are way too far outboard for learning to foil.

That said, a formula board sans straps is pretty much THE BEST platform to learn on. The fin box is strong enough to carry a deep tuttle foil, the board is wide and stable, and the volume is high enough for easy uphauling. The weight is race-light to enable easy pumping. If you need to tack or jibe while off the wing, it is very easy and comforting. The only downside of a formula board is that the finbox is often too far aft, which requires you to stand way back there to balance the foil.

I agree about the video. His footwork is way different from that of other jibers, but I think it is easier and more straightforward. I will be trying it when winter is over up here in the frozen north.

Yes, Hess is Adrian Hessels. And both Adrian's are glad you got a laugh. My friends encouraged me to post something but I could not tolerate watching myself talk, so I figured watching 2 of me is only half as bad.

Going strapless has allowed me to quickly become comfortable wind foiling and after a couple of my friends have gotten injured in the straps I really believe it could be safer. The biggest drawback is its harder to carry the board

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segler said..
The obvious benefit to foiling strapless is that you can easily find the balance point without any preconceived locations on the board.

True enough. But if you have a foil setup where the straps and foil are in the right place, that has advantages, too - it makes sure your feet are in the right place. That can make things easier for beginners.
I usually foil strapless, but on occasion, I noticed that my feet were placed poorly (usually too far forward). A strap placed sideways over the center of the board as far back as possible helps to know the foot is far enough back without having to look down.

Looking at Adrian's video, it seems one advantage of the wider boards is more room for your feet in a jibe. Having the feet next to each other when stepping back to minimize height loss makes sense. With a narrow-tailed board, it's much harder to step back onto the center line. But if you place the foot on the other side, you'll weigh the other rail, and the wobble will probably through you off.

Can't wait to get to a warmer spot and try some more foil jibes!

Yes, that is also true. Footstraps, if correctly located for windfoil balance, definitely FORCES you to put your feet in the right spot. No need to hunt for the right spot. I always use the front footstraps for exactly this reason.

Here's a video where the presenter uses a model suspended by a string to demonstrate how the balance changes with changes to: foot strap placement; sail mast foot placement; body weight; foil mast placement on a track; etc.

That's heliboy 999. He posts here occassionally. He just posted his part 2. He has a unique approach to footstraps. He makes the openings as large as possible so he can move his feet in them. Its sort of inbetween the footstraps/no footstraps arquement for beginner foiling.

LOVE seeing others posting in this thread. Please keep it up!

I am pretty much done for the year. 2 weeks ago I went out with my I99/48 set up on my Levitator 160, with a 4.8 Duotone super session. Had a great session, although a bit short. The wind was strong enough that I decided I need to add yet another sail to my quiver. I found a 2012 Sailworks Revolution 3.9 for a good price.... may pull the trigger on it. At $165 it seems like a good deal, plus I can afford a used mast and a booms for something that small, and not break the bank. I've spent a small fortune on this sport since my first flight.... but I don't regret it at all.

Funny thing about this sport: you spend money (laughing).

Up here in the northern hemisphere, we have pretty much also stopped the water sports for the season (except frozen water in the mountains).

Despite that, I did get out to try some foiling near my house on the Columbia River. The wind was 5 gusting 40 mph. It was pretty hard to get any rides at all. The air was 66 deg F, and water 44 deg F. It was that warm air that sucked me out there onto the water.

Oh well, you get days like that. Being on the water is always better than NOT being on the water. Even frozen water.

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segler said..
Funny thing about this sport: you spend money (laughing).

Up here in the northern hemisphere, we have pretty much also stopped the water sports for the season (except frozen water in the mountains).

Despite that, I did get out to try some foiling near my house on the Columbia River. The wind was 5 gusting 40 mph. It was pretty hard to get any rides at all. The air was 66 deg F, and water 44 deg F. It was that warm air that sucked me out there onto the water.

Oh well, you get days like that. Being on the water is always better than NOT being on the water. Even frozen water.

I'm several hundred miles north of you and the good days just got started for us, so it's all a matter of perspective.
Then again I'm not going to foil in this weather. Winter is wave season.

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segler said..
Funny thing about this sport: you spend money (laughing).

Up here in the northern hemisphere, we have pretty much also stopped the water sports for the season (except frozen water in the mountains).

I've seen foils loosen wallets that haven't spent a nickel on new gear in years - including me.

For those of us not in the northern northern hemisphere, we're still windsurfing. The southern northern hemisphere is in the meat of its windy season. (Neoprene required)

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segler said..
Funny thing about this sport: you spend money (laughing).

Up here in the northern hemisphere, we have pretty much also stopped the water sports for the season (except frozen water in the mountains).

Despite that, I did get out to try some foiling near my house on the Columbia River. The wind was 5 gusting 40 mph. It was pretty hard to get any rides at all. The air was 66 deg F, and water 44 deg F. It was that warm air that sucked me out there onto the water.

Oh well, you get days like that. Being on the water is always better than NOT being on the water. Even frozen water.

Yes in deed! I was on frozen water today, more or less snow. Great session on the windski! Very gusty! First session of the season. We had 5- 40 mph winds today too in Southern Oregon in cascades. Fell off a few times when the gusts were high.

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segler said..
Funny thing about this sport: you spend money (laughing).

Up here in the northern hemisphere, we have pretty much also stopped the water sports for the season (except frozen water in the mountains).

Not in California!

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boardsurfr said..
I had somehow missed Adrian's jibe video, but find it quite helpful. His emphasis on the foot placement is different from other foil jibe instruction I've seen, but makes a lot of sense to me. I think it's worth posting the video again here:

Thanks for saying I make sense, but I am sure my wife would disagree .

Thought I would try to provide some additional information about some of the conditions I took the video in. The shots from above where in "under powered" conditions and I was trying to demonstrate a broad reach to broad reach jibe. You can see that my stance is quite aft and hence my rear foot placement through the jibe would be on top of the rear straps. While the last jibes in the video, with the nose mounted view, are on a "powered up" day and my body and foot position is slightly further forward. I think what I am trying to highlight is that the transition foot placement seems to move depending on speed and/or wind strength.
Also I hope you notice that my steps are generally small and near the centreline , again this is made easier by not using foot straps.

Hope this makes sense, as it is alway hard to try and explain something in writing

If I had frozen water here i would be out Ice sailing too. Used to do the same on a skateboard during the light wind summers in a super market car park, much to the disgust of the shoppers lol. Weather has turned cover here now so hoping for a 7 degree plus day to tempt me out.

I remember then how easy it was to pump the skateboard to some amazing speed in almost no wind. Some great road rash from falls in board shorts and a tee shirt. At least snow sailing means you have lots of clothing too protect.

And looking at an earlier post.
I didn't spend any money of windsurfing kit for almost 15 years. Was mostly kiting and even that had 4 years with no kit replacement. This foiling thing has totally got me back into the sport and I feel the same buzz as when I started 30 years ago. There are more foilers than windsurfers at our beaches now and there faces that haven't been seen for many year who have come back to this new element of the sport.

When the wind gets stronger, do you guys drop in sail size or front foil size first? I only use my i99 and i84 wings currently, mainly because the next wing down for me is a Gamma 68 (FWIND1) I believe. I fear it may be faster than I am ready for.
Recently I was out in wind i couldn't handle with a 3.8 Sailworks Revolution and the i84 front wing. It had to be blowing 25 to nearly 40mph in the gusts. I thought about the gamma 68, but just didn't feel i was ready for the speed and how differently it may handle.

Maybe now that the water is warmer I will have to try the 68 and a bigger sail than I'd normally use.

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excav8ter said..
When the wind gets stronger, do you guys drop in sail size or front foil size first? I only use my i99 and i84 wings currently, mainly because the next wing down for me is a Gamma 68 (FWIND1) I believe. I fear it may be faster than I am ready for.
Recently I was out in wind i couldn't handle with a 3.8 Sailworks Revolution and the i84 front wing. It had to be blowing 25 to nearly 40mph in the gusts. I thought about the gamma 68, but just didn't feel i was ready for the speed and how differently it may handle.

Maybe now that the water is warmer I will have to try the 68 and a bigger sail than I'd normally use.

I do what ever is needed to ride the i76. So if that means keeping the same sail and dropping from i99 as wind increases I do that. But if wind picks up I will stay on i76 until I hit 3.7m. I can ride that combo in very strong wind (~25knots) if the water is flatish.

It has been a while since I used the gamma 68 but I don't think it was that much faster than the i76

This last weekend we had a decent blow of around 30+

My smallest sail is a 4.0 and I use the Time Code 68 wing, in B with 42 rear. My foiling buddy has the i65 wing but I haven't tested that size yet (the wing tips keep having unfortunate accidents).

The overall curved shape of the TC68 and the carving abilities are staggering, I never feel over foiled on it and I have been in 35+ on this wing easily.

Got another solid session in yesterday. 2 hours and 55 minutes of fun on my i84 with my 4.8 Duotone Super session. Overpowered at times, but still manageable. Should have gone in and put the Gamma 68 wing on and tried that. But as usual, I was having so much fun, I didn't want to come in. I am going to assemble the Gamma on my new switch fuselage so it's basically ready to go the next time it blows.

Hi I'm looking to get into foiling and have a little windsurf experience. I want to try and invest wisely. If I was going to invest in a newer foil oriented board I would be more tempted to get a twin U.S box as it seems a better engineering solution. However with a dedicated windfoil board such as the Naish hover ws, can I assume that it cannot be sailed like a normal windsurfer to start with or if foiling becomes too difficult? Or would I be better buying an older board with deep Tuttle that can take a fin or foil until I'm better?

The twin track boards are really a great thing for flexibility and versatility. They have a huge fore and aft adjustment range that allows you to try a huge universe of different foil brands and types. And, yes, some people on these fora have found that that you can mount two fins (US box) and fin-sail with them.

All that said, if you want to ease into this sport with a minimum of expense, get an old used formula board. It will have deep tuttle that is strong enough for a foil, be floaty enough to keep you up out of the water if necessary, and take a big range of sail sizes. Then you can put pretty much any old deep tuttle foil on it. The only downside is that the footstraps are too far outboard to learn on. So, start out strapless. It works. After 180 sessions I still ride a formula board with just the front footstraps. Back straps are off.

Sails. Don't worry about sail types and such. If the sail works at all, it will work for foiling. Sizes of 5.0 to 7.0 cover most conditions.

By the way, about that "minimum of expense." If you get hooked on this sport, "minimum of expense" is out the window. Be ready for it.