In 2000, the Surf-Foil was created. Many names such as Laird Hamilton and Dave Kalama are among the forerunners. Originally, it was a means of sliding on the water in surf-traction in large swell waves. It was Kai Lenny who blew up the number of surfers in 2016. The discipline quickly won over surfers from Hawaii, California, Australia, California and Brazil. THE level of this sport has increased dramatically. Foil surfing was eventually introduced in Europe and France. THE foil surfing offers new sensations and increases the number of sessions. This article will describe the operation of a foil of surf and its different parts. We will also discuss the importance of the features present on the front fender.
This article will explain how a foil works for the following sports: Surf Foil (SUP Foil), Downwind SUP Foil (Downwind SUP Foil) and Tow-in Foil.
Composition of a surf foil
THE Foil consists of the following elements: fuselage, mast, front wing, rear wing and stabilizer.
THE mast attaches perpendicular to the fuselage and the board. The wings are therefore parallel to the board. This allows you to control the foil simply by pressing down on your feet.
The front fender has a flat bottom surface and a curved top section (upper surface). The front wing has an elongated leading edge that gradually increases in thickness and tapers off at the rear end. The width of the front wing (from the center line of the leading edge to the center of the trailing edge) and its length (right/left end) is called “chord”.
The horizontal stabilizer is similar in shape to the front fenders and has the same properties. It has a smaller surface and a different profile.
Principles of operation of a foil
Fluid dynamics is the basis of how the foil works. As the front wing moves forward, it is pulled up by fluid dynamics. The water molecules on its upper surface accelerate to catch up with those on its lower surface (which is shorter because it is flat). The depression is caused by the acceleration of molecules in the upper part of the wing. The slowing of those of the lower part creates an overpressure. This creates an upward suction effect. The foil is “pulled” upwards at a faster speed (with the same profile and the same angle).
It is easy to compare the operation of the Foil to that of an airplane. The shape of the Foil is almost identical if we forget the mast or the board. The speed of movement creates lift, which allows take-off. The wings of the plane have an angle that allows it to stabilize in the air. A decrease in the speed of movement allows a decrease in lift, which makes it possible to land an aircraft (at a constant angle of incidence). To change the angle of attack, the pilot can use alternating pressure on the front or back foot to raise or lower the foil, or stabilize it. Everything depends on the pressure applied to the supports.
The speed should be enough to lift the front wing enough to allow the board to take off. The board takes off when there is a high angle of attack due to pressure on the back foot. To stabilize the board, the pressure on the front leg makes it possible to obtain a lower angle of incidence. This allows the board to lift and accelerate.
The swell is a source of energy
The suction force of air molecules is used by the plane to lift the board. However, water molecules have a higher density than air and the foil therefore uses them. This density increases the lift of the foil (the upward suction action) and its speed.
Surf foil consists of using the movements of the water (wave, swell and trough, wake of the boat) to fly. Unlike the wind, which allows the kite and the windfoil to use a constant force out of the water, the movements of the waves are variable forces with precise areas of lift on the water.
The practitioners of Surf Foil must leave the foil on the ground on the board and row to ride the wave. In SUP Foil, we leave the straight board and we row with a paddle to surf on the wave. Once on the wave, the speed generated by the slope of it will allow you to take off.
HOW CHARACTERISTICS AFFECT FOIL VARIATION
It’s all about fluid dynamics. Every little detail or modification of the foil can have an impact on its characteristics and its importance. We are going to focus on 4 main characteristics of a Foil of surf to show how they are affected (there are many other parameters, but we won’t discuss them here).
The lift of the foil, or upward suction, is largely dependent on the size and shape of the front wings, their thickness and their angle of incidence. The more lift a thick wing generates, the greater its surface area. The foil will slow down if it has a higher angle of incidence. However, it generates more lift if it has a larger surface area. The lift is lower if these parameters are lower. Two airfoils with identical surfaces, angles and thicknesses will produce different lift and speeds. There only way to determine if a profile is heavy or light is to use the surface as a reference parameter.
The lift of the foil will depend on the specificity of the profile of its front wing. It can be the top curve or the side curve. One that goes lengthwise from side to side.
Other external factors, such as rider weight, board size and wave power, also affect the overall lift of the foil.