fonctionnement d'un foil de surf foil nos explications en images

How a Surf Foil works : our illustrated explanations

The Surf-Foil appeared in the 2000s. Among the precursors, there are great names like Laird Hamilton, Dave Kalama or Paolo Rista. Originally, it was just a way to fly over the water in surf-traction, in large swells. In 2016, it was Kai Lenny who blew away the number of practitioners. The discipline immediately conquered Hawaiian, Australian, Californian and Brazilian surfers. The level is skyrocketing. Progressively, foil surfing is arriving in Europe, and in France. The advantages of the Foil are to multiply the number of possible sessions, of practicable spots, and to offer new sensations. We will explain in this article the functioning of a surf foil with its different parts and we will detail the importance of the characteristics of the front wing.

This article explains how a Foil works for the following sports: Surf Foil, SUP Foil, Downwind SUPFoil and Tow-in Foil.

Composition of a Surfing 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. Thus, the wings are parallel to the board. In this way, it is possible to act on the foil by simply pressing the feet.

The front wing has a curved upper surface and a flatter lower surface. The front wing has a rounded leading edge that quickly increases in thickness, then tapers to a thinner trailing edge. The chord is the width of the front wing (from the center of the leading edge to the center of the trailing edge) and the span is the length (the right/left end) of the wing.

Finally, the stabilizer has a shape quite similar to the front wing, with equivalent properties. However, it has a reduced surface and a different profile.

 

Composition of a Surfing Foil

TheFoil 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. Thus, the wings are parallel to the board. In this way, it is possible to act on the foil by simply pressing the feet.

The front wing has a curved upper part (upper surface) and a flatter lower part (lower surface). The front wing has a rounded leading edge that quickly thickens, then tapers to a thinner trailing edge. The chord is the width of the front wing (from the center of the leading edge to the center of the trailing edge) and the span is the length (the right/left end) of the wing.
Finally, the stabilizer has a shape quite similar to the front wing, with equivalent properties. However, it has a reduced surface and a different profile.

Tutoriel Sroka Company expliquant le fonctionnement d'un Foil

Operation of a physical foil mechanism

Principles of operation of a Foil

The operating principle of a foil surfing is a matter of fluid dynamics. The front wing is pulled upwards as it moves forward, as the water molecules passing over the top surface of the front wing accelerate to catch up with the water molecules passing over the bottom surface (which is shorter because it is flat). The acceleration of the molecules on the upper part of the wing creates a depression and the slowing down of those on the lower part creates an overpressure. The consequence is an upward suction effect. The higher the foil speed, the more the foil is “pulled” upwards (with equal profile and angle).

We can easily compare the functioning of a Foil to that of an airplane, which has more or less the same shape if we forget the mast and the board. The speed of movement believes a lift and allows to take off. The difference in angle given to the wings of an aircraft allows to stabilize in the air. The decrease of the displacement speed allows to decrease the lift and therefore to land an aircraft (at constant angle of incidence). Finally, to change the angle of incidence of the foil, the rider can alternately press the front or rear foot to raise or lower the foil or the stability. It’s all about the right amount of pressure on the supports.

To take off, the speed must be high enough to create a lift force on the front wing. Combined with a high angle of incidence (thanks to a pressure on the back foot) the board takes off. to stabilize, a pressure on the front leg allows to decrease the angle of incidence, thus the lift and to accelerate.

operation incidence angle surf foil

 

The wave as a source of energy

If the plane uses the suction force of air molecules, the foil uses the suction of water molecules which have a much higher density than air. This density will increase the lift (the upward suction effect) of the foil with speed.

We speak in this article of Surf Foil thus of use of the movements of water (wave, swell, hollow, wakes of boat) to fly. In opposition to the wind which allows in kite or windfoil the use of a constant force external to the water, the water movements of waves are variable forces with lift zones
precisely located on the water body.

Operation of a physical foil mechanism

operation surf foil lift mechanism

 

It is thus for the practitioner of Surf Foil to leave lengthened on the board with the foil below and to row to take a wave (in SUP Foil one leaves directly upright and one paddles with the paddle to take the wave). Once on the wave, the accumulation of the speed generated by the slope of this one allows the takeoff.

 

The Surf Foil and Downwind Foil in pictures

 

HOW THE CHARACTERISTICS OF THE FOIL VARIES


When it comes to fluid dynamics, even the smallest detail or change to the foil is important and affects its characteristics. We are interested in 4 major characteristics of a Surf Foil to explain which parameters influence them


(there are many others but we won’t go into them in this article).

 

Lifting capacity

The lift of the Foil, or the upward suction effect, varies primarily with the size of the front wing, its thickness, its airfoil shape, and its angle of incidence. The larger the surface area of a wing with thickness, the more lift it generates. The higher the angle of incidence, the more lift it generates but the more it slows down the foil. On the other hand, the lower these parameters are, the more the lift is reduced.
With equal surfaces, angles, thicknesses, two different profiles will result in different lift and speed. The surface as the only reference parameter is not sufficient to determine if a foil has a lot of lift or not.

Indeed, the specificity of the front wing profile will play on the general lift of the Foil. It can be the upper curve of the upper surface or the lateral curve that goes from one side to the other in the direction of the length.

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

détails de paramètres de portance du foil selon profil

 

Speed

Along with the lift of the foil, the speed of the foil depends on the area and the angle of incidence of the front wing. A front wing with a small area and/or 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 plays on the speed of the Foil. A wing with less chord and therefore more span will be faster. In addition, the profile of the wing (parameters mentioned above) is very influential on the speed and on the ability to accelerate.

envergure du surf Foil

Finally, as previously mentioned: the weight of the rider, the size and the weight of the board 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 (i.e. large surface area, wing thickness and a little angle of incidence) will be more stable than a slower, faster foil.

The main elements allowing the Foil to gain stability are the length (chord) of the front wing, its thickness and the surface and span of the rear wing, also called stabilizer.

The rear wing (stabilizer) plays a full role in stabilizing the Foil. Its lift is opposite to that of the front wing and thus slightly counteracts the lift of the front wing by creating opposing forces to stabilize the whole 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 water on which the Surf Foil is practiced. An agitated body of water with current, backwash and breakers will be more unstable because these elements disturb the depressions and overpressures that generate the upward attraction of the Foil
(like an air disturbance when flying).

 

Maniability

If a foil with little lift (therefore little surface, angle of incidence and thickness) is faster and indirectly more maneuverable, this is not the only parameter that affects its handling.

The most important element concerning the handling is the shape of the front wing, namely the side curve, which is accentuated to make it easier to turn with the foil.
A high side curve will result in a more maneuverable but slower foil because for the same amount of lift (shadow on the ground) the total area will be larger and will brake.
Conversely, a flatter side curve will turn less but will be faster.

 

IN SUMMARY:

The general shape and dimensions of the Foil vary these four characteristics

  • The bigger the wing, the thicker the angle of incidence = the more it carries and the less it goes fast
  • The smaller the wing, with little thickness, little angle and little chord compared to its span = the faster it is
  • The bigger and thicker the wing with more chord length = the more stable it is
  • The smaller, thinner and more curved a wing is, the more manageable it is

 

OUR CHOICES FOR THE DEVELOPMENT OF S-FOIL

When we developed our S-Foil, we spent months of R&D and testing to find the best compromise of accessibility, versatility and performance.

ailette freeride pour foil

Accessibility

Our vision is to democratize board sports by offering easy-to-learn and easy-to-improve products that are affordable on the market and have excellent overall performance. We have particularly worked on our S-Foil with an easy, error-tolerant and stable wing profile to accompany each practitioner as easily as possible.

To achieve this, we have increased the surface area, chord, span and thickness of the front wing compared to our previous models to gain lift and stability. We also reworked the stabilizer by adding surface area, side curve and a better surface thickness curve to maximize glide.

 

POLYVALENCE

With the influx of equipment available today, the choice of versatility was a natural one. 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 is by soliciting our athletes and combining our R&D efforts that we were able to test the S-Foil for more than 6 practices in very different conditions with users who do not have the same size. With 6 interchangeable front wing sizes (M 1250, L 1500, XL 1750 and XXL 2000 and 2 high Aspects) we have developed a hyper versatile foil that adapts: to the practice and the conditions but also to the size and level of each person.

Performance

If the choice of accessibility and versatility does not always go hand in hand with performance, we have worked on the profile of our wings on the details that make the difference in order to obtain exceptional performance qualities for each size of front wing.

To gain speed and maneuverability 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 the main beam back…We twisted the curvature profile of our wings to gain both stability and speed. Finally, we have validated our different sizes (surfaces) of front wings to gain speed and performance when the conditions of practice and the level of each user allow to switch to a smaller size.

Explications sur le fonctionnement d'un Foil de Surf

 

THE INFLUENCE OF THE BOARD ON THE BEHAVIOR OF THE FOIL

 

Length

The length of the board will influence your surfing in two ways. A longer board with volume makes it easier to catch waves and take off. However, a long board decreases the lift of the foil by one time in the air compared to a short board because of the extra weight at the front.

 

Width

The width of the board can, as well as the length, make it easier to take waves with the oar for take-off. On the other hand, once in flight, the rails of a board that is too wide may touch the surface of the water in the turns and slow down the rider.

 

Weight and Volume

The weight of the board has a negative influence on the lift of the board. The heavier the board,
the more the lift of the foil will be countered (opposing force)
. On the other hand, a gain of volume allows to take off better on the waves.

 

Form

One can rightly imagine that the shape of the board doesn’t matter much once in the air, but several details enhance the flying experience: the rocker at the front and the bevel at the back and sides to avoid touching the water once in flight. In addition, 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 in comfort of oar and to be more effective in the catch of wave.

 

OUR CHOICE OF SURFBOARDS/SUP FOIL

planche de foil surf

 

Planche de Surf Foil Fast Flyer

The Fast Flyer is designed for easy and efficient surfing. We opted for comfortable dimensions of 4’6 (140cm) long by 21″ (55cm) wide. With a rounded nose, and a compact overall volume, it is the perfect size compromise to learn, progress and perform in all conditions.

To make rowing easier, we have slightly hollowed out the deck for more comfort with a progressive rocker on the nose. We worked on the hull with a double concave to maximize the glide at low speed in order to start on waves that have not yet broken. The entire deck of the board is covered with pads for added comfort and strength. Once in flight, the bevelled rails and the cut tail allow to not touch the surface during the turns and when the user pumps. Its short length allows it to be very responsive and stable in curves, in addition to reducing inertia when pumping. For those who want to

Comment choisir sa planche de SUP Foil

SUP Foil range Sky Rider and Sroka Air

We have developed the Sky Rider range to combine performance and versatility. Our 7’8×30 allows you to practice up to 6 sports: SUP Foil, Wing Foil, Paddle Surf, Windfoil, Windsurf and Wake Foil. The generous dimensions of the board and its volume of 120 L make it easy for everyone to learn to foil. The Sky Rider 6’3 and 5’8 will convince the more experienced SUP sailors, and will allow the practice of Wing Foil and Wind Foil. Some people also like to travel light. For this we offer inflatable foil boards. The Air 6′ and 6’4 are perfect for both SUP and Wing Foil.

 

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