How does Surf Foiling works : our illustrated explanations

Surf foiling appeared in the 2000’s when watermen like Laird Hamilton, Dave Kalama or Paolo Rista imagined this way of flying over large swells on a towed surfboard with snowboard boots. Updated in 2016 by Kai Lenny, this discipline quickly gained ground over Hawaiian, Australian, Californian and Brazilian surfers, whose level rose very quickly. The discipline is slowly starting to develop in France and in Europe and the Functioning of a Foil is intriguing more and more people. the Surf Foil brings undeniable advantages to its users by maximizing the number of possible sessions and practicable spots that are not interesting in classical surfing but also by offering new flying feelings. We will explain in this article How does Surf Foiling works with its different parts and we will detail the importance of the characteristics of the front wing.

This article explains how does surf foiling works for the following sports: Surf Foil , SUP FoilDownwind SUP Foil and Tow-in Foil.

First of all, Surf Foiling and Downwind SUP Foiling in action

COMPOSITION OF A SURF FOIL

The Foil is composed of the following elements: mast, fuselage, front wing and rear wing (stabilizer).

The mast is attached perpendicular to the board and the fuselage so that it and the wings are parallel to the board to allow control of the Foil from the board by foot pressure. The mast and fuselage are connecting elements of the Foil to the board.

The front wing has a curved upper part (extrados) and a flatter lower part (intrados). The front fender has a rounded leading edge, which quickly thickens and then tapers towards a thinner trailing edge. The width of the front wing  goes from the center of the leading edge (stopping point) to the center of the trailing edge and the “span” is the length (the right / left extremity ) of it.

HOW DOES A SURF FOIL WORKS

The operating principles of a surf foil is related to fluid dynamics. The front wing is pulled upwards as it moves forward because the water molecules that pass over the upper convex (extrados) of the front wing accelerate to catch up with the water molecules passed on the intrados (which is shorter because it is flatter). The acceleration of the molecules on the extrados of the wing creates a depression and the slowing down of those on the lower part creates overpressure resulting in an upward suction effect. The higher the Foil speed is, the higher the foil is “pulled” upwards (with equal profile and angle).

We can easily compare how a surf foil does work to the functioning an airplane which takes on more or less the same shape if we forget the mast and the board. The speed of movement increases lift and allows you to take off. The difference in angle given to the wings of an airplane allows it to get stable in the air. The reduction in the speed of movement makes it possible to decrease the lift and therefore to land an aircraft (at constant angle of incidence). Finally to change the angles of incidence of the foil, the rider can do it by transfering his weight on the front or back foot to raise or lower the foil. It’s all about finding the right balance of weight on each foot.

To take off, the speed must be good enough to create a lift force on the front fender. Associated with a high angle of incidence (thanks to a pressure on the back foot) the board takes off going down the wave. To stabilize the rise, a pressure on the front leg decreases the angle of incidence, therefore the lift and helps to accelerate.

USING THE WAVE AS A SOURCE OF LIFT

The plane uses the suction force of the air molecules but the foil solicits the suction of water molecules which have a density much higher than those of air. This density will further increase the lift (the upward suction effect) of the foil with speed. We are talking in this article about How does Surf Foiling work, therefore using water movements (wave, swell, bumps, boat wakes) to fly. In opposition to the wind which allows in kite foiling or windfoiling the use of a constant force external to the water, the movements of water of the waves are variable forces with zones of lift precisely located on each one.

It means that the Surf Foil rider has to prone paddle on his board with the foil underneath to take a wave (on SUP Foil they start directly standing up and paddle with the paddle to take the wave). Once on the wave, the accumulation of the speed generated by the slope of it allows takeoff.

HOW DOES SHAPE CHARACTERISTICS OF THE FOIL INFLUENCE ITS PERFOMANCE

When it comes to fluid dynamics, the smallest detail or change made to the Foil matters and influences all its characteristics. We looked at 4 major characteristics of a Surf Foil to explain which parameters influence them (there are many others but we will not discuss them in this article).

THE LIFT

The lift of the Foil, or the upward suction effect, varies mainly depending on the size of the front wing, its thickness, its profile shape and the angle of incidence. The larger the surface of a wing is with thickness and the more it generates lift. The more positively the angle of incidence is, the more it generates lift but slows down the foil. On the other hand, the lower these parameters are, the more the lift is reduced. At different surfaces, angles, thicknesses, two different profiles will lead to different lift and speed. The surface as the only reference parameter is not enough to determine whether a foil is lifting a lot or not.

Indeed, the specificity of the profile of the front wing will have an effect on the general lift of the Foil. It can be the upper curve of the extrados or the lateral curve, the one that goes from side to side lengthwise.

Finally, other external elements come to play on the general lift of the Foil such as the rider’s weight, the weight and size of the board used or obviously the power of the waves.

Speed

Paralelly to the lift of the Foil, its speed depends on the surface, thickness and the angle of incidence of the front wing. A front wing with a small surface area and / or little thickness will offer more speed, and a front wing with less angle of incidence will also be faster.

Then, the specificity of the shape of the wing for the same surface has a major effect on the speed of the Foil. A wing with less width and therefore more wingspan will be faster. In addition, the profile of the wing (parameters mentioned above) has a major influence on speed and the ability to accelerate.

Finally, as mentioned above: the rider’s weight, the size and weight of the board used but also the power and the speed of the swell are external factors which strongly condition the speed of the Foil.

 

Stability

A relatively slow Foil with a lot of lift (therefore large surface area, wing thickness and a little angle of incidence) will be more stable than a less load and faster foil.

The main elements allowing the Foil to gain stability are the width of the front wing, its thickness and the surface and span of the back wingg, also called stabilizer. The back wing has a big role in the stabilization of the Foil. The longer and bigger it is with the right angle, the more stable but slow the foil is in general.

Its lift angle is opposite the front wing’s one and thus makes it possible to slightly counteract the lift of the front wing by creating opposite forces to stabilize the entire foil.

The external factors influencing the stability of the Foil are necessarily the weight of the practitioner and his technical skills but also the type of waves or bumps on which the Surf Foil is practiced. An agitated water with current, backwash and surges will be more unstable because these elements disturb the depressions and overpressures which generate the attraction towards the top of the Foil (like an aerial disturbance when in a plane).

 

Maniability

If a Foil with little lift (little surface area, angle of incidence and thickness) is faster and indirectly more responsive and easy to turn with, this is not the only parameter which affects its maniability.

The main element concerning the maniability remains the shape of the front wing, namely in particular the lateral curve, which accentuated makes it possible to turn more easily with the Foil. A high lateral curve will give a more manageable but slower foil because for the same lift surface (shadow on the ground) the total surface will be larger and will be slower then. Conversely, a more flattened lateral curve will turn less but will be faster.

 

TO SUM IT UP :

The general shape and dimensions of the Foil have an influence on these 4 characteristics.

  • The bigger the surface, thickness and incidence angle of a front wing are = the stronger is the lift but the slower it is
  • The smaller the surface, thickness, width and angle are compared to a long wingspan = the faster it is
  • The bigger the surface a a front wing is with lots of thickness and width = the more stable it is
  • The smaller the surface of a front wing is, without too much thickness and with lots of lateral curve = the more responsive and easier to turn it is

OUR CHOICES OF DEVELOPMENT FOR THE S-FOIL

When we developed the S-Foil during several months of R&D and tests in all conditions, our priority was to find the best compromise of : accessibility, versatility and performance.

ACCESSIBILITY

Our brand philosophy is about the democratization of board sports as much by the offer of easy to learn and to progress with gear as by their affordable  price on the market while having excellent general performance. We especially designed our S-Foil with an easy, mistake-tolerant and stable wing profile to carry each rider along its evolution in a very easy way

For this, we increased the surface, width, wingspan and thickness of the front wing compared to our former foils to gain lift and stability. We reworked the stabilizer by adding surface area, lateral curve and a better thickness curve on the surface to maximize the glide.

VERSATILITY

In front of the the massive amount of foiling equipment that can be found these days, the choice of versatility came naturally. And we mean versatility in terms of type of practice (Wake, Wing, Surf, Kite, etc.) but also in terms of conditions (wide wind ranges and all types of waves).

It was by soliciting our athletes and combining our R&D efforts that we were able to test the S-Foil for more than 6 different foil practices under very different conditions with riders of different weight. With 4 interchangeable front wing sizes (M 1250L 1500XL 1750 and XXL 2000) we have developed a hyper versatile foil that adapts: to the practice and to the conditions but also to the size and level of each rider.

PERFORMANCE

If the choice of accessibility and versatility does not always go in the direction of performance, we have worked the profile and shape of our front wings on the details that make the difference in order to obtain exceptional performance qualities for each size. To gain speed and maniability we chose fast, efficient and very stable profiles and we paid attention to all the details to reduce drag and friction by refining the trailing edges and moving back the midship beam.

We twisted the curvature profile of our wings to gain both stability and speed. Finally, we validated our different sizes (surfaces) of front wings to naturally gain speed and performance when the conditions of practice and the level of each user allow to go to a smaller size.

THE INFLUENCE OF THE BOARD ON THE FOIL PERFORMANCE

LENGTH

The length of the board will affect your Surf Foil practice in two ways. A longer board with volume makes it easier to paddle to take off on the waves However, a long board decreases the lift of the foil once in the air compared to a short board because of the excess weight at the front.

WIDTH

The width of the board can, like the length, make it easier to take off on the waves. On the other hand, once in flight, the rails of a board that is too wide risk to touch the surface of the water when cornering and to slow the rider or make him fall.

WEIGHT AND VOLUME

The weight of the board negatively affects its lift. The heavier the board is, the more the lift of the foil will be countered (opposing force to the suction). On the other hand, a gain in volume makes it possible to take the waves more easily, as long as it doesn’t imply a too big gain of weight.

SHAPE

We can rightly imagine that the shape of the board is not important once in the air, but several details can improve the flying experience: the rocker at the front and the bevel in the back and on the sides so as not to touch the water once in flight. Moreover, other parameters such as the rounded shape of the nose and the concave on the deck and under the hull make it possible to gain paddle comfort and to be more efficient in taking waves.

OUR CHOICE FOR SURF/SUP FOIL BOARDS

FastFlyer 4'6 SROKA

SURF FOIL BOARD FASTFLYER 4’6×21

The latest addition to the range and available only on pre-orders, the FastFlyer is designed to allow an easy and efficient foil surfing practice. We opted for comfortable dimensions of 4’6 (140cm) long by 21 ”(55cm) wide. With a rounded nose and a compact overall volume, this is the perfect size compromise for learning, progressing and performing in all conditions. To make paddling easier, we have slightly dug the bridge for more comfort with a progressive rocker on nose.

We worked the hull with a double concave to maximize gliding at low speed in order to set off on waves that have not yet broken. The entire deck of the board is covered with pads for more comfort and resistance. Once in flight, the beveled rails and the cut tail make it possible not to touch the surface during turns and when the user is pumping. Its reduced length allows it to be very reactive and stable in carves.

HYBRID SURF/KITE BOARD 5’2×20

Following our success in kite foiling, we developed a hybride board allowing to practice both Kite Foil and Surf Foil. This 5’2 × 20 has a good compromise of length, width and volume to take waves and take off easily. We worked the hull with a double concave.

The beveled rails also prevent you from touching the water once in flight. Finally, the progressive rocker and the slightly hollowed bridge at the front (under the thorax) allow you to row comfortably and efficiently. It’s a board that goes fast on the waves and handles well once in the air.

SUP FOIL SKY RIDER RANGE

We have developed the SKY RIDER range in order to bring even more versatility and accessibility. Our 7’8×30 is a Swiss army knife board allowing you to practice up to 6 board sports from the same board: SUP Foil, Wing Foil, Paddle Surf, Windfoil, Windsurf and Wake Foil. The generous dimensions of the board and its volume of 120 L allow riders  of all levels to learn Foil easily regardless of the practice and to stand on the board with a perfect stability no matter the conditions.

For 2020, we have developed two new SKY RIDER sizes dedicated to WING Foil and SUP Foil: the 6’3 x 29 ″ (120 L) ideal for getting started and progressing quickly, and the 5’9 x 26 ″ (90 L) for performing and reaching the highest level.

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