How to surf Foil

Surf-Foil emerged in the 2000s. Among the pioneers were such great names as Laird Hamilton, Dave Kalama and Paolo Rista. Originally, it was just a way of flying over the water in a surf-tow, in large swell waves. In 2016, it was Kai Lenny who made the number of practitioners explode. The discipline immediately conquered Hawaiian, Australian, Californian and Brazilian surfers. Surfing levels soared. Gradually, foil arrived in Europe and France. The advantages of Foil are that it multiplies the number of possible sessions and spots, and offers new sensations. In this article, we’ll explain how a foil works, with its various parts, and we’ll detail the importance of the front wing’s characteristics.

This article explains how a Foil works for the following sports: Surf Foil, SUP FoilDownwind SUP Foil and Tow-in Foil (towed waves).

The operating principle of a foil surfboard is based on fluid dynamics. The front wing is pulled upwards as it moves forward, as water molecules passing over the top surface of the front wing accelerate to catch up with water molecules passing over the bottom surface (which is shorter because it’s flat). The acceleration of the molecules on the upper part of the wing creates negative pressure, while the slowing of those on the lower part creates positive pressure. The result is an upward suction effect. The higher the speed of the Foil, the more the foil is “pulled” upwards (with equal profile and angle).

We can easily compare the operation of a Foil to that of an airplane, which takes up much the same shape if we forget the mast and the board. The speed at which it moves creates lift, enabling it to take off. The difference in angle given to an aircraft’s wings enables it to stabilize in the air. Decreasing displacement speed decreases lift, enabling a plane to land (at a 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 a question of adjusting the pressure on the supports.

To take off, speed must be sufficiently high to create lift on the front wing. Combined with a high angle of incidence (thanks to pressure on the back foot), the board takes off. to stabilize, pressure on the front leg reduces the angle of incidence, thus reducing lift and accelerating.

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

Secondly, the specific shape of the wing for the same surface area affects the speed of Foil. A wing with less chord and therefore more span will be faster. In addition, the wing’s profile (parameters mentioned above) has a major influence on speed and ability to accelerate.

Finally, as mentioned above, the weight of the rider, the size and weight of the board and the power and speed of the swell are external factors that strongly influence the speed of Foil.

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

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

The rear wing (stabilizer) plays a key role in stabilizing the Foil. Its lift is the opposite of that of the front wing, thus countering the lift of the front wing by creating opposing forces to stabilize the whole foil.

The external factors influencing the stability of Foil are of course the rider’s weight and technical ability, but also the type of water on which Foil surfing is practiced. An agitated body of water with current, backwash and breakers will be more unstable, as these elements disrupt the depressions and overpressures that generate the upward pull of the Foil (like an air disturbance when flying).

While a Foil with little lift (i.e. little surface area, angle of incidence and thickness) is faster and indirectly more maneuverable, this is not the only parameter affecting its handling.

The most important aspect of handling is the shape of the front wing, in particular the side curve, which is accentuated to make it easier to turn with the Foil. A high side curve will make the foil more manoeuvrable, but slower, because for the same surface area of lift (shadow cast on the ground) the total surface area will be greater and will brake. Conversely, a flatter side curve will turn less, but faster.

The wingspan also influences handling. The bigger the wingspan, the longer the foil will glide, but the tighter the curves. It’s a bit like a longboard and a shortboard.

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

• The bigger and thicker the wing, and the greater the angle of incidence, the greater the lift and the lower the speed.
• The smaller the wing, the less thickness, angle and chord relative to its wingspan = the faster it is.
• The wider the wing span, the longer it will glide and the more efficient it will be at pumping.

• The bigger and thicker the wing and the longer the chord, the more stable it is.
• The smaller, thinner and more curved a wing is, the more manoeuvrable it is.
• The wider the wing span, the less manoeuvrable it will be.

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

If the choice of accessibility and versatility doesn’t always go hand in hand with performance, we’ve worked on the profile and shape of our wings to find a compromise between easy pumping, long gliding and maneuverability.

By adapting fuselage length and stabilizer size, we can make a foil much more maneuverable, and thus achieve a compromise between glide, pumping ease and foil maneuverability. This is what we’ve done with the UHA range, and combined with shorter fuselages, we get an almost perfect compromise.

Length

Board length will influence your surfing in two ways Foil. A longer board with more volume makes it easier to catch waves and take off. However, a long board reduces the lift of foil once in the air compared to a short board, due to the extra weight at the front.

If the choice of accessibility and versatility doesn’t always go hand in hand with performance, we’ve worked on the profile and shape of our wings to find a compromise between easy pumping, long gliding and maneuverability.

By adapting fuselage length and stabilizer size, we can make a foil much more maneuverable, and thus achieve a compromise between glide, pumping ease and foil maneuverability. This is what we’ve done with the UHA range, and combined with shorter fuselages, we get an almost perfect compromise.

Width

The board’s width, like its length, can make it easier to paddle into waves for take-off. Once in the air, however, the rails of a board that’s too wide are likely to touch the surface of the water during turns, slowing the rider down.

Weight and volume

Board weight has a negative influence on board lift. The heavier the board, the more the lift of foil will be counteracted (opposing force). On the other hand, more volume means better lift off the waves.

Shape

It’s easy to imagine that the board’s shape doesn’t matter much in the air, but there are several details that enhance the flying experience: the rocker at the front and the bevel at the back and sides to keep the board out of the water. Other parameters, such as the rounded shape of the nose and the concave on the deck and under the hull, make for more comfortable rowing and more efficient wave catching.