SHAPESHIFTER CURVES, FLATS & EDGES
The hard working trio of surfboard design
As innocent as these three words sound, they pretty much sum up what makes a surfboard ride and feel the way it does and why one board goes differently from another. It’s fascinating how these three components present themselves in so many different parts of a surfboard and how they affect the interaction of the water flow from a breaking wave when coupled with the application and placement of weight through the rider’s feet. These three facets are largely responsible for why your surfboard goes great in some waves and not so great in others!
The modern shortboard is made up almost entirely of curves with a small amount of edge. The edge is easy to spot, starting on the rail around the front fins and running back around the tail. More alternative modern shapes will likely feature flats in addition to curves and edges. It’s fair to say that edges always occur between two or more curves or between a flat and a curve. It’s these edges that mostly define the modern surfboard. The presence of edges together with the amount of curve used is often what sets the modern surfboard apart from its older counterpart. Prior to the mid 1970’s you would have to look much harder to find a surfboard with an edge, not so these days.
When it comes to curves, the most apparent to the eye also happens to be the longest; this curve forms the perimeter or plan shape of the board, also known as the outline curve. The outline curve is also the curve with the most variation in its form. The width of the surfboard at given points together with the tail shape determine what form this curve will take. Sometimes it undulates through melted wings, sometimes the outline curve will be intersected by an edge as is the case of a more defined wing. Some surfboards have reverse curves known as side cuts contained as part of their plan shape.
Next longest is the rocker curve with it’s nose lift, flowing into a flatter curve throughout the body of the surfboard and then lifting again as it sweeps off the tail.
The third curve that runs from nose to tail is the deck curve and the shape of this curve is often hidden under layers of wax and deck grip yet provides an incredibly important function. This nose to tail deck curve works mostly as a volume distributor. Running across the deck from rail to rail are also curves which distribute volume as well as forming the rail shape.
All in all, curves are either blending into other curves and flats or stopping at an edge. Therein lays the key: curves give a board its characteristic personality while edges give the board its attitude! As different in concept as curves and edges are, they work together.
"Curves tend to hold onto water and control speed and direction while edges break water, releasing it from the board. If its curve that allows a board to turn into an arc, then its edges that give a clean crisp feel to the entry and exit from that arc."
Curves tend to hold onto water and control speed and direction while edges break water, releasing it from the board. If its curve that allows a board to turn into an arc, then its edges that give a clean crisp feel to the entry and exit from that arc. Edges enhance the speed and provide the spark, accentuating the power in a turn by increasing the drive from it. Shapers may increase the amount of curve in various parts of a surfboard to design in personality to a board and then off set the exaggeration by adding in an edge to counteract or reduce any negatives or residual lag affects. Edges give the ZING!
A big chunk of what we feel coming back to us through the soles of our feet has to do with the contours of the bottom surface of your board. While these can be isolated and defined at any point along the length of the board these curves are usually changing and blending into differing amounts of curve to perform different functions ahead of, directly under, or behind a rider’s foot. We can only really describe these curves when we measure them at a certain point or as an isolated feature: we may see a concave for example or we may see a rolled bottom or a Vee containing double concaves. Now here’s an interesting point: curves are curves even though they may look completely different, say for example the difference between a roll contour and a concave contour, these contours are both made up of curves its just that their respective high or low points are reversed. A stock in trade modern shortboard is likely to have a concave which has it’s lowest points where it dissipates hence defining it’s position rail to rail and fore and aft. With a single concave its lowest points are out towards the rail while its highest point is at the stringer line. This high point defines the depth of the concave and also has the function of flattening out the rocker curve adding planning speed under foot.
An interesting point about concaves is that even though they are in themselves a curve, they can have the affect of flattening out the curve that they are shaped into i.e. the rocker curve. So in this case adding the curve of the concave into the curve of the rocker creates speed. In the opposite scenario where a roll contour is used the opposite will occur. . . . .
Think of the curve in your surfboard a bit like the curve in the waves you ride. If your wave is steep and bowling it will have more energy and be faster moving, there will be a curve in the face more like a concave shape. Waves like this can propel a board with more curves like roll contours and overall rocker curve. This is why boards with accelerated tail rockers light up in steeper waves and take on a lively feel they may lack in waves that are slow moving and fuller faced. A board that’s de- signed for waves like this may feel sluggish in weaker flatter faced waves.
The “sweet spot” in a surfboard is governed by the make up of curves under the rider’s feet: rocker curve plus contour curve equals longer or shorter sweet spot.
What you see when looking at a surfboard is not so much curves, flats or edges in isolation but rather a continuous seamless skin. You are looking at complex compound curves blending and changing to form the surfboard shape as a whole. We shapers however tend to dissect the board at chosen intervals into a series of one dimensional components that we can more easily define. Once assembled the surfboard shape takes on its completed form. You can de-construct your surfboard using a straight edge and your eye to discover curves, flats and edges over the surface of your board. Even in a board made up entirely of curves you will likely find flats that occur at the intersection or overlay of curves running in different directions as they blend together. When a surfer tilts their board into the face of a wave these “secret” flats come into play adding sensations of speed and drive. So, next time you surf, have a think about what you feel and how that relates to what you saw with the straight edge. It may help you to understand and connect with your surfboard in a more meaningful way.