It's not just in using bigger wings for flight in 11-15 knot gusts.
The lower drag of smaller foils allow for smaller sails to attain foil speed.
Increased drag from big foils need more sail power to get thru it's drag phase to attain foiling speed.
Look at foil racers. For the lightest 6-13 knot days, while they use 9 meter sails, the choice of wing is still around a 100cm wide, maybe 1,000 sq cm area front wing.
Lower drag has to account for something.

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LeeD said..

The lower drag of smaller foils allow for smaller sails to attain foil speed.

This is only true if you get out of the board drag/wave drag hole. I think, based off of how the board feels, that the I99 pushes the board up enough that I am out of the wave drag hole and just need to pump a little bit to ride the foil. With the I76, I need more speed, and the board is causing too much drag to get over the hump and onto the foil. The I76 isn't lifting up enough to help me overcome that wave drag unless I've got a lot of sail up and the board starts quasi planing itself. Maybe with a wider board I could ride the 76, like closer to a meter instead of 77cm width of the Blast.

Small foils make lots of sense for top end speed for minimal drag, but you need a wide board to get early planing and to hop over the wave drag problem of the board. I'll have to watch more foil racing videos to see what's going on with those.

I foiled the Gamma 68, then the I76 and now a 1700cm2 wing on a 72cm freeride windsurf board with low tail volume. Largest sail is 6.3, I'm up and going in 10-12kts and I'm at least 200# in gear.
Your issue is pumping technique. Likely just wagging your back hand without any leg involvement. You can spot these sailors because they don't get flying very early and they tire quickly.

That said LeeD is entirely wrong about wing size and low speed drag. High aspect low area wings require large sails and volume to get useable bottom end, their lack of drag is only a factor once foiling at high speed. I've run both types on a low volume board and the difference was staggering.

I'll try to get better videos of pumping technique of myself. I can drop my rear quite far to thrust my hips but i need a bigger sail. With the 6.6, i need more wind to counterbalance, or my timing between sail and legs may be way off

I use the Naish Kitewing, 2019, 600 sq cm.
Same wind as I use the WS 2018 wing 1220 sq cm.
Naish 73 cm 122 Hover. Don't know about right or wrong, but both work for 6-14 knot breeze.
My buds, smaller than me, are using 1050 NP's and i76 with similar sail sizes.
I AM lightweight, but up to 30 lbs. heavier than my foiling buds.
I am also 17-40 years older than them.

Here we go, found one spot where I pumped just above the planing threshold with the i76 but probably stopped pumping too soon.

I'm sure there's plenty to criticize technique wise

.be

Try to get in the front strap while pumping. If you have problems with this remove all straps and try to get your weight more back

Looks to me like your back foot could be further back and your front foot in the strap.

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aeroegnr said..
Here's the math. The 99 takes off around 8mph or so, and lift is linear with area but squared with velocity. So, if 8mph is right, then takeoff speed of the 76 is right around 10mph by the math. It's too close to tell in the footage I have of myself though.

This is assuming that lift coefficient and weight difference is insignificant. Weight probably true, and because they are similar design it seems like the lift curve will also be quite similar.

That's probably a good first approximation, but not the whole story. The i99 has only 15% more area than the i84, which would give a 7% difference in takeoff speed. That would be less than 1 mph. But foilers who have both wings usually report a larger difference.

In the mathematically framework, that would probably be reflected by a higher lift coefficient for the i99. One way to look at that is that the wings have similar areas where the flow is more disturbed (the center and the outside wings), but the i99 has a larger area in the middle. The i99 also seems to have a sharper (and thus less draggy) trailing edge. The i99 also seems thinner than the i84, although that should effect top speed rather than takeoff speed, unless the i84 is too thick.

But in the end, the square relation of speed to lift will overwhelm the linear relation between lift and lift coefficient, so we're probably talking about differences like 7 and 10 mph vs. 8 and 10.

There's a fun way to see what the minimum speed of foils: have a cell phone announce the speeds to you through an app like "Talking GPS Speedometer" or WindsportTracker. That works well for foiling since everything is so quiet. Getting the takeoff speed may be hard since the speed changes quickly once you get on the foil, but you can get a good idea of the stall speed in lulls, when speed changes are more gradual.

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PatK said..
Try to get in the front strap while pumping. If you have problems with this remove all straps and try to get your weight more back

Definitely. foiling is not like windsurfing where you progressively move further back as the board starts to plane. The key to foiling is finding the balance point mostly foil mast position versus combo of sail mast and front foot strap, assuming the foil is unchanged. For the board to foil you need to be standing in balanced riding position. Therefore in front strap

Agree with removing back strap for now.

There is a little bounce or "ollie" of the board that will pop the board onto the foil, at lower speeds.

If you are still not lifting move foil forwards

At age 72 and 195 lb I have no trouble getting the i76 up into flight with a 6.8 in 12 mph winds (just barely the onset of whitecaps), and I'm no youthful jock that can pump like crazy. In my book (and this is just my book, I know), the i84 and i99 are overkill for light winds when the i76 is plenty.

In any of these wind sports, you have to have enough energy in the wind to get you moving. No move, no fly. The wind kinetic energy is a squared function of wind velocity. As a result wind of 12 mph has 2.25 times the energy of wind at 8 mph. Expecting to fly in 8 mph wind, even with a monster sail and monster wing, is wishful thinking.

The i99 might get flight at 11 mph, and the i84 at 11.5 mph (ok, let's be optimistic and call it 10 mph and 11 mph, respectively). You need board speed to fly. You need wind to get board speed.

Waiting to see a couple whitecaps out there with a i76 and 6.8 has worked for me. If I don't see at least a couple odd whitecaps, I go fishing.

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aeroegnr said..
Here we go, found one spot where I pumped just above the planing threshold with the i76 but probably stopped pumping too soon.

I'm sure there's plenty to criticize technique wise

.be

I won't criticize your technique because I don't know enough to do that so I want to share one thing about my pumping technique (or lack thereof). I have a formula board and a infinity 84 wing. I weigh 75 kilos and mainly use my sailworks NX 8.2 4 cam sail. when I pump, I am WAY more aggressive than you and bring the sail much closer to my chest (I Bend my arms much more than you). I sometimes start with very little pumps but as soon as I am at take off speed, I start pumping with bigger movements. Also, if the wind is pretty light, I will be pumping for much more time than you. Oone more thing, mast carbon content has a big impact on the way you pump and the way the sail reacts to your pumping. I think if you have the proper mast and the mast has high carbon content you could pump faster than with a lower carbon content because the mast with more carbon will react faster. I notice this with my 6.7 which I use with a 30% carbon content.

again, I am not sure if my technique is proper, just sharing what I do (and I works for me)

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aeroegnr said..
Here we go, found one spot where I pumped just above the planing threshold with the i76 but probably stopped pumping too soon.

I'm sure there's plenty to criticize technique wise

.be

I won't criticize your technique because I don't know enough to do that so I want to share one thing about my pumping technique (or lack thereof). I have a formula board and a infinity 84 wing. I weigh 75 kilos and mainly use my sailworks NX 8.2 4 cam sail. when I pump, I am WAY more aggressive than you and bring the sail much closer to my chest (I Bend my arms much more than you). I sometimes start with very little pumps but as soon as I am at take off speed, I start pumping with bigger movements. Also, if the wind is pretty light, I will be pumping for much more time than you. Oone more thing, mast carbon content has a big impact on the way you pump and the way the sail reacts to your pumping. I think if you have the proper mast and the mast has high carbon content you could pump faster than with a lower carbon content because the mast with more carbon will react faster. I notice this with my 6.7 which I use with a 30% carbon content.

again, I am not sure if my technique is proper, just sharing what I do (and I works for me)

Nico:

Board is planing...pilot needs to step back.
Standing forward in slog position will keep him from flying, since slog position promotes slogging.

Thanks guys, I'll get into the front earlier and try to get more aggressive. Before, when getting more aggressive, I have either rounded up or gotten way off balance, but I'll keep trying to improve. I actually liked pumping the bigger sails more in light wind because they're a better counterbalance but I'll keep trying with my 6.6 because I've been able to fly the 99 on it.

BTW this is with the foil as far forward as I can put it for both the I76 and I99.

Front foot in the strap. When you release the sail pressure pull the foot up and when you pump the sail push it down/forward.
This results in being airborne with the sail in a position to add forward momentum rather than having no way to accelerate once you are up.
The sail pump which works best for me is hands together, front hand starts the pump; back hand finishes it and the mast is brought forward again before sheeting out.

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aeroegnr said..

LeeD said..
I'd suggest foiling more often to get in better shape.
I'm 71, often pump 10 or more to get up on foil, and do that at least 20 times each 1.5 hour session.
This foiling thing is supposed to be at least a little bit of excersize.

If anything it's pumping technique and lousy wind, I'm in pretty good shape and am actually down to about 190lbs (i'm 6'1 and am getting pretty lean) since I started this thread. I was going out twice a week on the I76 and getting zero flight time for a while.

The only person today that wasn't on a big wing like an i99 and flying was on an i84, and he looked about 20-30lbs lighter than me and considerably shorter. An older guy about your age was on an i99 and a 10.0 and he was sometimes flying. There were wingers out flying but I was quite a bit taller than them (and probably 20-30lbs heavier than them), and they all had big wings. It makes no sense when I'm taller and 20lbs over most of the other foilers to be on a smaller wing, especially as a beginner foiler.

Is that you, Greg? If so, I'm probably the older guy (64 years old/215lb). I was actually on an i84 with that 10.0 Speedfreak but just because I was too lazy to rig my 7.0 Flyer which would have foiled up just as early. I'm eager to try the i99 but never have. I do like running big sails because I truly hate pumping, but with big sails I bet I'd be happier with higher-aspect wings than Slingshot offers.

I thought you looked pretty smooth yesterday, with nice height control. On that huge sail I was either WAY up near breaching when I stood right over the board, or sort of semi-slapping when I hiked out in the straps. I did fly in both front and back straps for a while (a first - usually I'm just in the front strap) but never felt really balanced on the new board. Its balance is amazing on a fin, but I wonder if I should move my straps back for foiling?

We should be on small sails tomorrow!

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Awalkspoiled said..


Is that you, Greg? If so, I'm probably the older guy (64 years old/215lb). I was actually on an i84 with that 10.0 Speedfreak but just because I was too lazy to rig my 7.0 Flyer which would have foiled up just as early. I'm eager to try the i99 but never have. I do like running big sails because I truly hate pumping, but with big sails I bet I'd be happier with higher-aspect wings than Slingshot offers.

I thought you looked pretty smooth yesterday, with nice height control. On that huge sail I was either WAY up near breaching when I stood right over the board, or sort of semi-slapping when I hiked out in the straps. I did fly in both front and back straps for a while (a first - usually I'm just in the front strap) but never felt really balanced on the new board. Its balance is amazing on a fin, but I wonder if I should move my straps back for foiling?

We should be on small sails tomorrow!

Hah yeah that's me, and thank you! Yeah, so far much better control, I think you saw me when I was heading toward shore and up on the I99. You had some good gybes earlier when you were finning, made me upset I didn't bring my 9.5 yesterday.

I think I breached a couple times but it was a very gentle drop and never came off the board or catapulted, just kept going.

Yeah, tomorrow should be very interesting indeed!

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LeeD said..
Board is planing...pilot needs to step back.
Standing forward in slog position will keep him from flying, since slog position promotes slogging.

Another vote regarding the front strap. If your front foot is in front of it, you will not get off the water. Having your front foot in the strap would have and will make all the difference in the world. Basically, that's where you put your foot to get the board back on the water.

Thanks for posting the vid! Each time, it will get easier. We promise.

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aeroegnr said..
Here we go, found one spot where I pumped just above the planing threshold with the i76 but probably stopped pumping too soon.

I'm sure there's plenty to criticize technique wise

.be

honestly, did not look like you were pumping that much, I know you felt like you were, but in reality not much pumping of the board and really minor pumping of the sail.

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WillyWind said..

aeroegnr said..
Here we go, found one spot where I pumped just above the planing threshold with the i76 but probably stopped pumping too soon.

I'm sure there's plenty to criticize technique wise

.be

I won't criticize your technique because I don't know enough to do that so I want to share one thing about my pumping technique (or lack thereof). I have a formula board and a infinity 84 wing. I weigh 75 kilos and mainly use my sailworks NX 8.2 4 cam sail. when I pump, I am WAY more aggressive than you and bring the sail much closer to my chest (I Bend my arms much more than you). I sometimes start with very little pumps but as soon as I am at take off speed, I start pumping with bigger movements. Also, if the wind is pretty light, I will be pumping for much more time than you. Oone more thing, mast carbon content has a big impact on the way you pump and the way the sail reacts to your pumping. I think if you have the proper mast and the mast has high carbon content you could pump faster than with a lower carbon content because the mast with more carbon will react faster. I notice this with my 6.7 which I use with a 30% carbon content.

again, I am not sure if my technique is proper, just sharing what I do (and I works for me)

Seconded. For me pumping on the foil is way more aggressive than when on the fin. I agree with willy I can start small but if that doesn't work then it is very aggressive bending both elbows pulling the entire rig towards me. When I go back to the fin, I need to adjust my pumping to be more back handed.

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aeroegnr said..
Thanks guys, I'll get into the front earlier and try to get more aggressive. Before, when getting more aggressive, I have either rounded up or gotten way off balance, but I'll keep trying to improve. I actually liked pumping the bigger sails more in light wind because they're a better counterbalance but I'll keep trying with my 6.6 because I've been able to fly the 99 on it.

BTW this is with the foil as far forward as I can put it for both the I76 and I99.

FYI the 76 should be at least 6cm further back than the 99, assuming universal and straps are unchanged

Above it was said, "Another vote regarding the front strap. If your front foot is in front of it, you will not get off the water."

That obviously depends on where your front wing is located. If you have balanced your gear with a freeride foil such that the front foot in the strap is in the right place, then, yes, definitely use the front strap.

However, if you have simply replaced the freeride foil with a race foil (and keep the same sail), where the front wing is a good 20 cm further forward, you have to put your front foot in front of the footstrap to avoid uncontrollable lifting.

On my old formula board I have everything perfectly balanced for my freeride foils. When I mount my Moses Race to that board, I have to foil strapless with my front foot in front of the footstrap. If I try to use the front footstrap, I get a bucking bronco out there. (My formula boards have exactly one, and only one, mounting position for the footstraps. I don't have the freedom to move them.)

It is, as always, all about balance. If you set your gear up with the front wing at or near the midpoint between your front and back footstraps, you will easily foil in control with the front foot in the strap. If you have achieved this balance, then, yes, always-always use the front footstrap. It serves to locate your stance.

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segler said..
In any of these wind sports, you have to have enough energy in the wind to get you moving. No move, no fly. The wind kinetic energy is a squared function of wind velocity. As a result wind of 12 mph has 2.25 times the energy of wind at 8 mph.

It's a cubed function of wind velocity. A 12 mph wind has 3.375 times the power available for extraction than the 8mph wind.

but it also takes 33% more power to drive a board at 11mph than at 10mph. (Assuming drag of the non-planing board goes up with the square of velocity -a huge assumption = but if it did). 10% more wind will get you that extra mph. It's going to be hard to measure!

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Ian K said..
It's a cubed function of wind velocity. A 12 mph wind has 3.375 times the power available for extraction than the 8mph wind.

That is incorrect with respect to foiling.

The idea that the energy is a cubed function of wind velocity seems to come from wind turbines. For example, home.uni-leipzig.de/energy/energy-fundamentals/15.htm shows how the power of the wind is a cube function, but the kinetic energy of the wind is a square function.

One intuitive explanation of this is from dr%C3%B8mst%C3%Brre.dk/wp-content/wind/miller/windpower%20web/en/tour/wres/enrspeed.htm: when the wind speed doubles, the power of the wind goes up with the square, but the speed of the turbine blades also goes up 2-fold, meaning the blade is hit by twice as many 'slices of wind", and "each of those slices contains four times as much energy".

Maybe some of Balz Mueller's duck tricks look a bit like a turbine, but I'm pretty sure he has the wing or sail depowered during the moves. For regular foilers, what matters is the aerodynamic lift equation, which has a square relation to the speed:


The screen shot above is from www.grc.nasa.gov/www/k-12/airplane/lifteq.html

Cubed or squared, it is definitely not linear. We need wind to move our gear. 8 mph is insufficient. 12 mph is sufficient.

Back to the physics. Above it says, "the power of the wind is a cube function, but the kinetic energy of the wind is a square function." I based my squared argument on the KE = 1/2*m*v*v equation. Power equals force times velocity. This is where the third velocity comes in.

Lift is not power. Lift is a force and is based on the velocity squared, as shown above.

Most important is standing on the sweetspot.
As in windsurfing, that spot is in between the footstrap options, NOT in front.

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boardsurfr said..

That is incorrect with respect to foiling.
The idea that the energy is a cubed function of wind velocity seems to come from wind turbines.

It's not incorrect and it's not just an idea. Lift or power? They are just 2 different applications of F=ma. There's a few other mathematical tricks based on F=ma that are useful at times. You'll get the same answer no matter which method you use.

Don't think you're going to even get close with mathematics on this one though. All that pumping going on.

Not much difference in a wind turbine and a sailboat. They use similar wings. One goes around in circles, one in a straight line.

Neither takes into account pumping...arms and leg.