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How to Surf Foil

Louis-Arnaud surf-foil in Mauritius, equipped with the Fast Flyer 4’6 board and the High Aspect 1190 Lift S-foil

  1. Composition of a surf foil
  2. Principles of operation of a foil
  3. How the characteristics of the foil vary
    1. Lift
    2. Speed
    3. Stability
    4. Manoeuvrability
  4. Our S-Foil Development Choices
  5. The influence of the board on the behaviour of the foil
  6. Our surfboards and sup foil

Surf-Foil appeared in the 2000s. Among the pioneers are big names such as Laird Hamilton, Dave Kalama and Paolo Rista. Originally, it was just a way to fly over the water in a surf-towed way, in large waves of swell. In 2016, it was Kai Lenny who made the number of practitioners explode. The discipline immediately conquered surfers from Hawaii, Australia, California and Brazil. The level is skyrocketing. Gradually, surf foil arrives in Europe, and in France. The advantages of Foil are to multiply the number of possible sessions, practicable spots, and offer new sensations. In this article, we will explain how a surf foil works 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 SUP Foil and Tow-in Foil .

Composition of a Surf Foil

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

The mast is attached perpendicular to the plank and 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 fin has a domed upper part (upper surface) and a flatter lower part (lower surface). The front wing has a rounded leading edge that quickly builds thickness and then tapers to a thinner trailing edge. The width of the front wing (the width from the center of the leading edge to the center of the trailing edge) is called “the chord” and the length (the right/left end) of the front wing is called “the chord”.

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

Tutoriel Sroka Company expliquant le fonctionnement d'un Foil

Principles of operation of a foil

The working principle of a surf foil is based on fluid dynamics. The front wing is pulled upwards as it moves forward, because the water molecules that pass over the upper surface of the front wing accelerate to catch up with the water molecules passed over the lower 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 overpressure. The consequence is an upward suction effect. The higher the speed of the foil, the more the foil is “pulled” upwards (at the same profile and angle).

We can easily compare the operation of a foil to that of an airplane which takes on more or less the same shape if we forget the mast and the board. Movement speed grows lift and allows take-off. The difference in angle given to the wings of an airplane Stabilizes in the air. LA decrease in the speed of movement allows you to reduce lift and therefore to land an aircraft (at a constant angle of incidence). Finally, to change the angles of incidence of the foil, the rider can by alternating pressure on the front or rear foot make the foil or the stability go up or down. It’s all about the amount of pressure on the supports.

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

Our best equipment for SURF FOIL

S-Foil High Aspect 1350 Lift Front Wing

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Le foil Hight Aspect très performant pour le surf foil vendu par Sroka Company au meilleur prix

S-Foil High Aspect 1190

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pack surf foil performance

Surf foil pack Fast Flyer + S-Foil High-aspect 1190

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Surf Foil 4'6 Fast Flyer

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Swell as a source of energy

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

In this article, we are talking about Surf Foil and the use of water movements (waves, swells, troughs, boat wakes) to fly. In contrast to wind, which allows the use of a constant force external to the water in kite or windfoil, the water movements of waves such as waves are variable forces with precisely localized lift zones on the water.

It is therefore a question for the Surf Foil practitioner to leave lying on the board with the foil underneath and to paddle to catch a wave (in SUP Foil you go directly standing up and you paddle with the paddle to catch the wave). Once on the wave, the accumulation of speed generated by the slope of the wave allows the wave to take off.

Surf Foil and Downwind Foil in pictures

manoeuvres en surf foil

HOW THE CHARACTERISTICS OF THE FOIL VARY

When it comes to fluid dynamics, every detail or change made to the foil matters and affects its characteristics. We looked at 4 major characteristics of a Surf Foil to explain what parameters influence them (There are many others but we won’t cover them in this article).

Lift

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

Indeed, the specificities of the front wing profile will play on the overall lift of the foil. This can be the upper curve of the upper surface or the lateral curve, i.e. the one that goes from side to side lengthwise.

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

Speed

In addition to the lift of the foil, the speed of the foil depends on the surface area 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 specificities of the shape of the wing for the same surface play on the speed of the foil. A wing with less chord and therefore more wingspan will be faster. In addition, the profile of the wing (parameters mentioned above) has a great influence on speed and acceleration ability.

Finally, as mentioned above: the weight of the rider, the size and weight of the board but also the power and speed of the swell are external factors that 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 bit of angle of incidence) will be more stable than a foil with less weight and a faster one.

The main elements that allow the foil to gain stability are the length (chord) of the front wing, its thickness and the surface area and wingspan of the rear wing, also known as the stabilizer.

The rear wing (stabilizer) plays its full role in stabilizing the foil. Its lift is inverse to that of the front wing and thus makes it possible to slightly counteract the lift of the front wing by creating opposing forces to stabilize the entire foil.

The external factors influencing the stability of the Foil are necessarily the weight of the rider and his technical skills but also the type of body of water on which Surf Foil is practiced. A rough body of water with currents, backwashes and waves will be more unstable because these elements disturb the depressions and overpressures that generate the pull of the foil upwards (like an aerial disturbance when you are in a plane).

Manoeuvrability

If a foil with little lift (i.e. little surface area, angle of incidence and thickness) is faster and indirectly more manoeuvrable, this is not the only parameter that affects its manoeuvrability.

The main element concerning the manoeuvrability remains the shape of the front wing, namely the lateral curve, which accentuated makes it easier to turn with the foil. A high lateral curve will result in a more manoeuvrable but slower foil because for the same lift surface (shadow cast on the ground) the total surface area will be larger and will brake. On the other hand, a flatter side curve will rotate less but will be faster.

IN SHORT

The general shape and dimensions of the foil vary these four characteristics:

  • The bigger a wing is, the thicker with the angle of incidence = the more it carries and the slower it goes
  • The smaller a wing is, with little thickness, angle and chord in relation to its wingspan = the faster it is
  • The larger and thicker a kite is with chord length = the more stable it is
  • The smaller a kite, the thicker it is with curve = the more manoeuvrable it is
Tutoriel et explications sur la manière dont un foil fonctionne

OUR S-FOIL DEVELOPMENT CHOICES

When we developed our S-Foil, we sought over several months of R&D and testing to achieve the best compromise in terms of accessibility, versatility and performance.

Accessibility

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

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

Versatility

Faced with the influx of equipment that can be found nowadays, 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 our S-Foil surf foil for more than 6 practices in very different conditions with users who do not have the same size. With 4 interchangeable front wing sizes (M 1250, L 1500, XL 1750 and XXL 2000) we have developed a hyper versatile foil that adapts: to the practice and the conditions but also to the size and level of each one.

Performance

While the choice of accessibility and versatility does not always go in the direction of 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 manoeuvrability , we have chosen fast, efficient and very stable profiles and we have paid attention to all the details to reduce drag and friction by refining the trailing edges and moving the master handsome 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 as soon as the conditions of practice and the level of each user allow us to switch to a smaller size.

THE INFLUENCE OF THE BOARD ON THE BEHAVIOUR OF THE FOIL

Length

The length of the board will influence your surf foil practice in two ways. A longer board with volume makes it easier to catch the waves to take off. However, a long board decreases the lift of the foil once 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 catch waves when paddling 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 turns and slow down the rider.

Weight & Volume

The weight of the board has a negative impact 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 in volume makes it easier to get off to the waves.

Shape

We can rightly imagine that the shape of the board doesn’t matter once in the air, but several details help to improve the flying experience: the rocker at the front and the bevel at the back and sides so that you don’t touch the water once in flight. In addition, other parameters such as the rounded shape of the nose and the concave on deck and under the hull make it possible to gain in paddling comfort and to be more efficient in catching waves.

OUR CHOICES OF SURFBOARDS/SUP FOIL

Fast Flyer Foil Surfboard

Our Fast Flyer foil surfboard is designed to allow an easy and efficient practice of Surf Foil. 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 compromise to learn, progress and perform in all conditions.

To make paddling easier, we’ve slightly hollowed out the deck for more comfort with a progressive rocker on the nose. We worked the hull with a double concave to maximize the glide at low speeds in order to set off on waves that have not yet broken. The entire deck of the board is lined with pads for comfort and durability. Once in flight, the beveled rails and cut tail ensure that the surface is not touched when turning and when the user is pumping. 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

Sky Rider and Sroka Air SUP Foil range

We have developed the Sky Rider range to combine performance and versatility. Our 7’8×30 board 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 how to foil. The Sky Rider 6’3 and 5’8 will convince the more experienced SUP Foil practitioners, and will allow the practice of Wing Foil and Wind Foil. Some also like to travel light. For this, we offer inflatable foil boards. The Air 6′ and 6’4 will be perfect for SUP Foil as well as Wing Foil.

Sky Rider 5’8 & 6’3

Sroka Air 6′ & 6’4

If you still have questions about this, or for any other request, please do not hesitate to contact us !

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