Hydrodynamics of surf fins

The hydrodynamics of surfing is a huge topic, see:: HYDRODYNAMICS OF SURFING,We will focus here on the role of surfboard fins and fins.

The dynamic surf fins ADAC™ system are a step forward technology which radically modifies the hydrodynamic approach of fins which equip the surfboards.

"This evolution of the active principle of the surf fin, mark a real revolution in hydrodynamics of surf fins by providing exceptional fluidity and the feeling of a board that sticks to the feet by responding instinctively to the slightest movement !."

" This technology of fins profiles with variable geometry brings in the maneuverability and acceleration provided by the fins in a new era !"

Let's sharpen our intuition of sliding, with a zest of technical and scientific argument...

So let's back up the description of this biomimetic fin technology, leaving the precise and quantified arguments of the designers, specialists in hydrodynamics, to establish the usefulness and innovative character of the ADAC patents.. (Adaptive Dynamics Attack & Camber US patent14859193/ 2015 & FR 1402226/2014 appliqué au surf par Fyn https://fynsurf.com/)

We will use the concept of static weight and "dynamic weight" to approach the hydrodynamic quality of a surf fin, The rigor would require us to use the concept of force rather than weight, but it is more intuitive to evaluate 1 kg earlier than 10 newtons, we therefore temporarily allow ourselves this popularization (using quotation marks), to keep an intuitive dimension when reading what follows:

• Static weight is easy to gauge, with a scale for example. This weight presents a widely used argument but it has a low impact on surfing performance: a glass of water drunk before (or during) the session is heavier than the maximum noticeable difference between 2 carbon or classic technology fins!
• The "dynamic weight" is visible only in action: it represents the resistance to progress which slows down the board. Thus a fin which presents an unsuitable angle, or which generates a stall, causes a drag and therefore a "dynamic weight" much more annoying and sensitive than its static weight:

We will see later in detail how the "dynamic weight" of a fin can go from 70 grams to 900 grams, in the same wave phases, if its camber and incidence do not adapt correctly to the direction of the fluid. ! A board equipped with 3 fins can therefore go from 0.2 to 2.7 kilograms of "dynamic weight"! To make matters worse, this increase in "dynamic weight" is often accompanied by a loss of lift performance.

The static weight variation between 2 types of fins, whose order of magnitude rarely exceeds 0.1 kg, therefore seems secondary because they represent around 30 times less than the "dynamic weight" variations. It is this type of analysis hydrodynamics who initiated the system ADAC .

This surf fin technology is the result of 3 areas of research & development that we will summarize here:

1. Historical study of the evolution of the fin in the practice of surfing: the genes to be preserved.

2. Theoretical study of the hydrodynamics, kinematics and mechanics of the fin problem.

• Advantages of the ADAC system.
• Analogy with the types of turns in Skiing or Snowboarding
• Influences of camber parameters and attack angles of hydrodynamic profiles.
• Influence ADAC on the drag of resistance to the advancement of surfboard fins.
• influence ADAC on the drag of resistance to the advancement of surfboard fins
• Influence ADAC on efficiency range and stalle.
• Influence ADAC on the acceleration of surfing.
• Influence ADAC sur l'accroche du rail par limitation de l'effet de dévers. 
• Influence ADAC sur la réduction on the reduction vortex losses (winglet effect).
• Influence ADAC sur la sécurité (ailerons anti coupures)

3. Intuitive prototype experience, and natural sensation seeking.

1:Study of evolution fins in surfing history:

les 11 Genes de base :

Before going further in the description of the system of fins and fins ADAC System™, and demonstrate the real contribution that it offers to the state of technique, check if this system integrates the best of what has been done in its genes .

Since 1934 (Tom Blake), fin designers have shown various forms with varied objectives. We will only mention 11 basic "genes" in the genealogy of the fin, because dozens of models deserve to be mentioned for their participation in this evolution. We have put aside the purely aesthetic factor, which remains an important argument in a medium where the effect of fashion has solid anchors. For a more in-depth study of the history of the fin, I invite you to consult the page:Since 1934 (Tom Blake), fin designers have shown various forms with varied objectives. We will only mention 11 basic "genes" in the genealogy of the fin, because dozens of models deserve to be mentioned for their participation in this evolution. We have put aside the purely aesthetic factor, which remains an important argument in a medium where the effect of fashion has solid anchors. For a more in-depth study of the history of the fin, I invite you to consult the page::https://www.surfresearch.com.au/f.html

Gene n°1:Continuous variation of the shape of the fin according to the conditions.

In the beginning, there were... waves and instinct:

Need creates the function of the fin instinctively, by varying the shapes of our hands to direct us in the wave. No historical trace of the inventor, we should look at the prehistoric level and certainly beyond in our genetic memory... or closer to us, in the sensation of the present moment.Need creates the function of the fin instinctively, by varying the shapes of our hands to direct us in the wave. No historical trace of the inventor, we should look at the prehistoric level and certainly beyond in our genetic memory... or closer to us, in the sensation of the present moment..

 

Gene n°2: The variations of the wing's incidence according to the need

In history, every sinner civilization has developed its own experience of waves and a way of sliding over them. We will not discuss here the anteriority of the discovery because the instinct of sliding is universal. Tales of travels in West Africa (1600) tell the agility of the boatmen in the waves, in this case, the oar serves as a drift that is oriented to steer the pirogue in the wave.:

 

Gene n°3: Here we will remember that hanging on the rail in speed, straight line, without transverse skid, our fin should not slow us down and only be forgotten.

The first surfboards observed during Cook's trips (1769) to the Sandwich islands describe finless long boards, and the first photography of surfers (1890 - Sandwich surfers, surf type alaia without fins) show us a finless Alaia shape.

nous montrent un shape Alaia sans dérive.

Surfboards will remain finless for long time, the rail is the only way to hang the wave.

 

Gene n°4:The fulcrum and the pivot allow the turn, but we will also remember that a technological advance must include security and ease of integration to be shared

But the need to take support to modify the trajectory without slipping (Slide) is real, and move their longboards without fin, old time surfers (1930-1940) briefly dive the foot in the water to turn the board... We attribute the invention of the surf fin to Tom Blake in 1934, salute to this genius surfer who embodies the creative spirit of the shaper/surfer. The implantation of this fin revolutionizes surfing by allowing new possibilities of tricks and movements. It stabilizes the trajectory and creates a support on a rear pivot to turn and change direction. But despite its undoubted effectiveness, this innovation proposed by Blake in 1934, takes time to be adopted, because of a relative difficulty of establishment and the danger which it represents in the eyes of the surfers, the fin will remain hidden for some years.

Photo and caption handwritten by Tom Blake. Surfer Magazine, March 1981

Gene n°5: The importance of the surface in the 1960s

From 1935 to 1960 the height of the fin continues to increase, the fulcrum is more and more efficient and allows more and more tight turns, the radicality of the cut back and the bottom turn are linked to this evolution.

1935-1960:

Gene n°6: What about security

n the 60's, the evolution of new materials allowed greater lengthening, and safety became an argument, we note in 1960 the POPOUT system which is expected the fin to be removed during a shock.

Gene n°7: One good fin is better than two opposites

Around 1964 while the Twin (2 fins) spreads, Greenought tests Twin fins and systematically bring closer, as long as it gains efficiency, it ends up bringing them closer so much that it finds that only one well sized fin is more efficient! No, the twin is not dead and the multi fin has a bright future ahead, but let's remember that less is more!

Gene n°8: Variable geometry depending on forces!

In the 70's, Greenought developed single fin, with a high elongation: to allow accumulated maneuverability, it decreases the width (chord of the profile) which induces a rail effect, and it increases the height (reduction in vortex losses) to maintain the surface which generates a support closer to the nose of the board. At the same time, it introduces the Rake (rearward angle) and the flexibility, the combination of which allows the geometry to change under constraint. The principle of Greenought: it lengthens, thins and gives rake to bend the tip of the fin in the direction of flow. A feeling of flexibility and fluidity in the maneuvers is introduced. This drive effect is proportional to the length of the fin, its rake and its flexibility (today we can find S-Wings fins working on this principle).

Warning, the exaggeration of this principle generates:

• Long, thin cutting sabers increasing the risk of injuries.
• Lift centers offset from the board, producing tilting and overturning effects, reducing the grip of the rail.
• A reversal of curvature of the upper surface which can induce the stalling of the leading edge.

 

Gene n°9 : Structure work

In 1977, Cundith worked on a structure combined with a material allowing flexibility of the surf fin.

Gene n°10: The importance of incidence and its adaptation to conditions

In 1998 Swivel Fin introduced an adjustable incidence concept which is certainly the result of a more scientific hydrodynamic approach to the performance of foils according to their incidence.

 

Now let's see how these genes reflecting the creativity of the shapers who preceded FYN surf, have been revisited! Let us also see how certain problematic aspects, revealed by the hydrodynamic analysis of the fin, were solved by the innovative genes of ADAC system: (Adaptive Attack & Camber System).

2: Theoretical hydrodynamic, kinematic and mechanical approach to the problem of the surf fin :

The specifications of a surf fin are particularly complex because it varies depending on the surfer, the board and the wave in constant transformation. The conditions encountered in the trajectory of a single wave: speed gain, grip, dynamic turns, curves, revival, pumping ... are all specific moments, where the functions of the surf drift vary and even oppose sometimes. We will see for example, that the dynamic weight (drag of resistance to advancement) of a single fin can pass, from 70 grams for a correctly oriented fin, to 900 grams if its camber and its incidence do not adapt to the direction of the fluid!

This dynamic evolution of the specifications of the surfboard drift, highlights the necessity and the major asset of the dynamic system with reactive biomecanic structure of ADAC system. Theoretical analysis and careful experimentation, combined with an uncompromising design strategy, led to the following exceptional results:

Advantages ADAC (Adaptive Attack Camber System):

• Automatic variation of the incidence and the camber generating a constant optimization of the finesse (lift / drag ratio) and the reduction of the "dynamic weight".
• Dynamic parallelism of the fins limiting drag and "dynamic weight" by providing permanent synchronization of the performance of each opposite fin.
• Ultra-fast lift from low angles of attack (120 newtons from 10 degrees for a speed of 14m/s - 31mph).
• Maximum grip only on demand due to variable camber controlled by forces generated by the surfer (progressive (negative and positive) camber variation range from 0 to 35%).
• Horizontal pumping, maximum speed gain due to a conversion of transversal movements in acceleration (Bilateral orientation of 45 ° of the projection of lift transforming all lateral components into propulsive force).
• Generation of thrust due to the undulating movements of the paddle phases.
• High position of the aileron lift centers favoring the grip of the rail by limiting the cant effect.
• Total erasure of the camber and the incidence in the rectilinear trajectories of the acceleration phases offering a residual drag ("dynamic weight") almost zero (0.7 newtons at 4m/s - 9mph).
• Multi-material biomechanical structure ensuring solidity, elasticity and safety due to the flexibility making cuts impossible.
• A "fusible" part calculated to deform when a force 2 times greater than the water can produce in the most radical maneuvers, is applied to the system. This fuse protects from knocking shocks and ruptured boxes.
• 5 different materials combined in an aeronautical technology structure composed an articulated kinematic chain allowing controlled elasticity and winglet effect.
• Advance of the axis of rotation at the level of the spine generated by the automatic incidence variation. This positioning of the fictitious axis of rotation allows a more balanced surfing position and engaged in maneuvers, inducing a more horizontal board glide favoring speed conservation.
• A new and instinctive feeling of the action of the ailerons thanks to their dynamic response to impulses and the alignment of the center of rotation on the spine which provides a real experience of intuitive and natural trajectories.

Analogy with the types of turns in Skiing or Snowboarding:

We can compare the turns with static fin and FYN surf fins, with skid or cut ski turns:

• At a higher technical level, the skidding turn has major drawbacks :
• It is not suitable for cornering at high speeds. Indeed, the centrifugal force is such that the surfer cannot stay in his trajectory.
• It does not allow a sufficiently precise control of the board.
• It does not allow you to rotate in a limited space.
• It is an important source of speed loss.
• It positions the body too far back to perform a quick raise.
• The cornering cut allows precise cornering at high speeds. The speed loss is very low. In addition, the support remains centered throughout the driving phase of the turn and control can be very effective and intuitive. The position of the body remaining centered and the recovery is immediate

Let's be more precise (if you still follow...) in the description, and let's get to the heart of the hydrodynamic problem of surfboards:

(>fig 1)

• Influence of camber parameters and incidence of hydrodynamic profiles:

The theoretical performances of the best hydrodynamic profiles are known and listed by specialists in databases (See Heliciel database), and we know how the performances of drag and lift vary according to the incidences, camber, and speeds.

• Symmetrical surf fin profiles:

There are effective profiles at low angles of incidence, but which suddenly drop off at the largest angles and this produces, for example, a loss of cornering support (stall or spin out) due to the increase in incidence caused by the curved trajectory. We will take for example here (fig 2.1) a symmetrical profile the NACA 0008.

(fig 2.1 : Profiles of fins_symmetrical surf fins)

Of which here (fig 2.2) is the curve of drag lift and glide ratio (lift/drag) as a function of the variation in incidence at a given speed for an aileron having this profile:

(fig 2.2: performances of symmetrical surf fins_fins)

• Profiles of cambered surf fins :

There are effective profiles at large angles of incidence, but which generate significant drag even when they have zero incidence, this is harmful for the acceleration phases. We will take for example here (fig 2.3) a cambered profile the NACA 9505.

(>fig 2.3:Profiles cambered surf fins)

Here is (fig 2.4) the curve of lift and glide ratio as a function of the variation in incidence at a given speed for an aileron having this profile::

(>fig 2.4: performance of cambered surf fins_fins)

Presentation of the curves (fig 2.2 and 2.4); in green the drag (Newtons), in blue the lift (Newton) in black the glide ratio (lift/drag ratio), with the horizontal axis varying the relative incidence from 0 to 90 degrees

• Influence of the ADAC system on the forward resistance drag of surfboard fins:

The comparison of the curves of these 2 profiles (fig 2.1 and 2.3) show a very low drag force (green curves) (0.7 newtons) at zero incidence for the symmetrical profile (fig 2.2 ). Whereas a cambered profile (curve fig 2.4) generates 8 newtons of resistance to progress.

In a straight trajectory there is therefore an obvious interest in using a symmetrical profile. To have an element of judgment, take the 2 opposite fins of a twin, with an angle of 4 degrees of incidence fixed by the shaper: 9+9=18 newtons of resistance, i.e. almost 2 kilos to push at the end of the legs :

The ADAC system aligns the fin at zero incidence and removes the camber when the trajectory is parallel to the axis of the board (it also retains the parallelism of the ailerons whatever the angle), therefore a delta of 18 -1.4 = 16.6 newtons of trail removed:

                

• Influence of the ADAC system on the lift:    

An arched profile therefore generates a significant lift force even at low angles of incidence (fig 2.4). The slightest slippage, or lateral displacement component, transforms the profile of the ADAC system into a cambered profile which generates more lift, therefore more camber, therefore more lift ...

The feedback effect of this grip loop generates an almost immediate recovery of the trajectory, which makes the system very reactive and reduces the time spent adjusting direction.

In our example a symmetrical fin (curve fig 2.2) must be placed at 40 degrees of incidence to generate 120 newtons of lift while the fin with variable camber of the ADAC systm already offers 120 newtons at 10 degrees (curve fig 2.4 ) and rises to 160 Newton at 15 degrees, i.e. an involuntary sliding amplitude at the rear of the board 4 times less for the ADAC system.

The variation in camber of the ADAC system therefore makes it possible to combine the performance of a symmetrical profile, which is optimal during straight paths or at very low incidence, with the performance of various profiles whose camber evolves to generate maximum liftings at from 5 degrees of relative incidence up to 25 degrees without sudden stall.

• Influence of ADAC system on the efficiency range and dropoutInfluence of ADAC system on the efficiency range and dropout:

Beyond about 30 degrees of incidence, whatever the shape of the profile, a phenomenon of hydrodynamic stalling more or less suddenly degrades the lift of a conventional fin (see curves fig 2.2 and 2.4).

The adaptability of the angle of incidence of the ADAC system (fig 1) maintain an optimal angle of incidence by pivoting the profile following the path of the fluid, maintaining effective relative incidences repelling the stall effect even in the tightest curves.

• Influence of ADAC system on acceleration:

The variation of the incidence and camber is programmed "mechanically" by a controlled elastic structure (aeronautical technology patented by FYN surf) forming an articulated kinematic loop: the kinematic chain of the ADAC system reacts lateral constraints when the trajectory incorporates a drift component. The kinematics of the ADAC system causes the tilting direction of the fin to tilt forward, generating a propulsion and acceleration. This lift projection generated by the ADAC system brings two major advantages:

• Creation of a natural ability to produce speed during particularly instinctive alternative lateral movements (pumping) comparable to a dolphin or fish tail movement.
• Accelerations during turns providing a dynamic trajectory opening up perspectives of figures that would be impossible without this technology.

• Influence of ADAC system on rail grip by limiting the cant effect

A center of thrust close to the board, limits its cant and the effort required to stick the rail in the wave. Long drifts unfortunately increase the tilting effect which tends to overturn the board when there is a lot of weight applied. The ADAC system provides drive and 70% more thrust thanks to its dynamic leading edge and camber, while keeping a center of thrust very close to the board in order to reduce the slope.

• Influence of the ADAC system on the reduction of vortex losses (winglet effect) :

Short wings with high lift emit marginal vortices which can degrade lift performance (vortex losses). Some birds, like eagles, have feathers at the end of their wings, forming an inclined surface exploiting and limiting these vortices. These flexible and profiled surface is integrated at the end of the ADAC fin structure to deform naturally under the effort of lift while respecting this principle.

• Influence of ADAC system on safety (anti-cut fins):

One of the major advantages of the ADAC system is that it increased performances and security. The observation from the analysis of the hydrodynamics of the fin is that high performance is not synonym of rigid and sharp structures. The fin profiles of dolphins or whales are proof of this. Their flexible structure generate optimal hydrodynamic forms adapting to the various propulsive phases:

The biomimetics (technology inspired by the biological study) of the ADAC system results from a detailed analysis of these ultra-efficient dolphins fins.

The elasticity of the materials forming the slender parts of the structure of the ADAC system, were exposed to "crash tests" showing the advantage of the flexible zones combined with the twisting of the structures to protect the body of the surfer in case of impacts with the fin.

Slow motion videos impact fuse protection tests copyright fynsurf.com:

the designers of the ADAC system opted for a controlled break, damaging the fin instead of the surfer or his board.

• Anti cut thanks to the flexibility of the slender parts..

• Protection against knocking impact and ruptured boxes:: a "fusible" part deforms at violent impact with solid bodies.

3:Intuitive prototype experimentation: The search for natural instinctive surf sensations:

• The biomechanical structure of the ADAC system generates an intuitive hydrodynamic surf experience with organic logic in impulse in phases.
• The addictive reactivity resulting of the patented the ADAC system and all tests sessions have optimized the acceleration pulses and sequences of trajectories.
• The fluidity of the body's instinctive movements in the curves generates the expression of the natural human marine instinct.

To share with surfers who are interested in the hydrodynamic approach and its arguments, I invite you to send your comments to

_contact@fynsurf.com_ JF Iglesias, Research and development - FYN surf.

Kenny Dorion, Design and communication -

FYN surf. ADAC Licensing & Patents Legal Contacts:

Europe patent attorney : Cabinet Gasquet 74000 Annecy France

USA patent attorney: CIONCA Law Group P.C. Irvine, CALIFORNIE 92614

To obtain ADAC system licenses in various hydrodynamic / aerodynamic branches, you can contact the owners of the Patents via _contact@fynsurf.com_

• website: FYN (https://fynsurf.com/)