Descripton and presentation of

We are free to invent our trajectories, but guided by our perception of the world, we surf it as we are, different in our certainties, our doubts, our culture, and fortunately, our imagination. To "shape" a board is to carve the tool of this freedom, to imagine the vessel that propels us into the wave. This tool gives us a grip in the present, fluid.. When it naturally serves our intentions, a board is intuitive. And if it inspires our trajectories, then it becomes magical! How do we objectively describe the qualities, or defects, of a shape if they depend on our subjective perception? How can we express our feeling of sliding, in useful diagnostics, and perfect the tool for our next trajectories? This software exposes detailed hydrodynamic arguments, applied to surfing, which can underpin the exchange of experience between the moment of surfing and the moment of shaping.

The analyzes of the functioning of surfboards differ according to the angles of observation and the tools of each one. These discrepancies are reduced by defining together the benchmark and the method of analysis. Hydrodynamics, applied here, establishes a benchmark relating to the surfer, and explains his method: the physical quantification of forces by variation of the quantity of movements, Cartesian analysis of the hydrodynamic elements of the surf, and the systemic analysis of the imbalance and return (or not) in balance, of the surfer in motion.

From ancient Greek: "water" húdrios and "powerful", "efficient" dynamikos, hydrodynamics teaches the art of efficient movement in water. By describing planing, this science offers the surfer a vision of the energy flowing around them. The mastery of this art is also exercised by sculpting the fluid lines of our shapes: a shape is beautiful when it is effective, because it guides or cuts the fluid smoothly, without unnecessary turbulence. The instinct of the shaper is expressed naturally, because capturing the energy of the water, or of the air, it is to imagine the flow approaching our wing, to adjust the angle, to adapt the curvature, while seeking the smoothness of the flight. The hydrodynamicist, the child shaper, or the surfer, strokes the river. He lives the intimate experience of a particle carried in the flow and a bird soaring in the invisible ascending flow. Immersed in the movement of the present, our instinct observes, experiences and argues our knowledge of the world.

But without memory, the study of fluids is a maze of parameters that cannot be mapped out in a single lifetime of experimentation. Fortunately, there are benchmarks that direct us beyond our individual experience. Let us observe the wave of knowledge, experimental and instinctive, propagated by Archimedes, Reynolds, Bernoulli, Lindsay Lord, Stavisky, Tom Blake, Bob Simmons and other beach encounters, like so many lives of curious children, having fun on the shore . The visions they breathe in us constitute our collective memory, it guides us in the timeless physics of the movement of water. Let's go through a few equations if necessary, but don't miss this swell of memory, this giant's shoulder of which we are all the humble heirs.

We naturally communicate our sensations by using images, even to describe abstract physical concepts: The surfer mimes acceleration by projecting his pelvis forward, he thus translates his desire to accelerate, rather than the result of an acceleration which would cause him to fall back. He speaks of a stretched water surface by striking his palm, to express the hardening induced by the dynamic pressure of the relative speed, at the moment of impact. To describe the curves, he poses, his arms swinging, and draws the trajectories by moving his center of gravity in space. In his mime, the surfer expresses balances and supports, which must be formulated precisely when analyzing the maneuverability of a board. But above all, this gesture reveals the objective that the surfer's gaze designates in the wave: A beautiful trajectory always begins with the direction of the gaze. This vector points to the origin of the reference, the reference that the hydrodynamicist must integrate, to match his analysis with the reality of the surfer: The Still-point.

The surfer and his board gravitate around the “Still-point”, so the path proposed here does the same. We will draw on this concept of surf culture, to extract from its mythology, a concrete physical reality establishing our landmark in the wave. Relative velocities in waves are discussed in some references [(Bascon), (Hendricks), (Kinstle) (Anderson, Brewer, Lis, & Mctavish), (N. Lavery), (PAINE)], which express the importance of the chosen frame of reference. By observing the Still-point in motion, the dynamic description of the surf offers useful insights for the surfer and the shaper.

In the raking light of this landmark, we will understand how a board translates our intentions into trajectories. We will describe the intuitive nature of a board by listing the maneuverability parameters that govern its dynamics. We will propose numerical methods, arguing the hydrodynamic phenomena of the active elements characterizing a board. We will also propose avenues for optimization, applied to the rails, nose and fins.

Here is a surf analysis toolbox. It results from hydrodynamic works, surf sessions, Wakesurf experiences, exchanges, reading, and the development of fluid software integrating the intuitive logic of surfing. This is the workshop notebook of an apprentice surfer-shaper developing and refining his method of designing and analyzing surfing. Certain redundancies and turns of phrase will prove to the reader that the author is a technician without literary pretensions. But a benevolent and curious reading, will perhaps find in these notes, the inspiration of beautiful trajectories. If you find there some methods clarifying your vision, sharp arguments to express your intuition, or simply a lever favoring your creativity, the objective of this synthesis will be achieved. If you find my little lath plane there, in the middle of a pile of shavings, please bring it back to me.

JF Iglesias

Experimental shaping session “Hydroactive Project” Photo: Nd Surf Guéthary France