Bottom contour
Ask a thousand shapers how the bottom of a surfboard works, and it’s likely you’ll get a thousand different answers. There is perhaps no other part of surfboard design theory that is both more complex and poorly understood than how various types of bottom designs work. The reason for the confusion is twofold. First, few details are known about how water actually flows along the bottom of a board, because the wetted bottom of the board is constantly changing speed and direction in relation to the moving medium of water that makes up the wave. Meanwhile, the water in the wave itself is constantly changing speed, direction and shape, while water molecules on the surface of the wave behave differently than water below the surface. This creates a highly dynamic, variable and complex condition that makes it difficult, if not impossible, to replicate in a laboratory in the hope of collecting hard data that has any significant theoretical implications.
The second reason why bottom design is poorly understood has to do with rider perception and style (or lack of it!). Two different riders may ride the same board, and get two different ideas of how the design works, based on what their expectations are, and the body mechanics of how they actually ride a surfboard – how far apart their feet are, how they distribute their weight on a turn, where their center of gravity is, where they stand on the board in relation to bottom contours, etc. Add to this all the other variables a surfboard brings to the table (rail shape and volume, foil, flex, fin setup, etc.) and you have very little hope of sorting out what effects should be attributed to the bottom design, and what should be attributed to other elements of design.
Still, there is some general agreement about the performance characteristics of some of the most basic bottom contours typically seen on today’s surfboards, as they have been used successfully for decades. But whether certain bottom contours and combinations of contours work is a different question than how they work, and so much of what we know about bottom design is based largely on anecdotal evidence from riders who’s feedback is considered reliable and respected, and not on hard physical data. This chapter will discuss bottom contours from both perspectives – the physical and theoretical principles of how bottom designs work, along with the cumulative anecdotal feedback from respected surfers and shapers over generations.
Bottom Design Basics
Most shapers divide all bottom design features into three theoretical categories: flat, concave and convex. Each bottom shape gets its name from how the bottom would appear if you were to look at a cross section of the board. Some people may have a tendency to imagine a flat or concaved bottom as being flat or concaved both from nose to tail and rail to rail. This is not so. Due to the rocker of the board, the “flat” or “concaved” bottom is really only flat or concaved in one dimension – rail to rail. Therefore, concaves create a bottom with a compound curve – a curved surface within a curved surface – while flat bottoms create simple curves – a flat surface on a curved surface. So… flat bottom features are simply flat areas of the bottom of the board that run across the cross section, perpendicular to the rail. Concave bottom features are those features that raise the bottom of the board above the bottom of the rail, creating concaved area(s) of the bottom shape perpendicular to the stringer. Convex bottom features are those that lower the bottom of the board below the bottom of the rail. Both concave and convex design features, when compared to simple flat bottoms, slightly increase the distance of the line that stretches from rail to rail (the shortest distance between two points is a straight line), but do not necessarily increase wetted surface. But, because convex bottom features add volume to the bottom of the board, they tend to displace water at low speeds, and are commonly referred to as displacement features, whether or not they cause the bottom of the board to increase or decrease wetted surface.
Flat, concave and convex bottom design features are not mutually exclusive, but are commonly used in combination with each other on a single board to fine tune performance. Like most design features, simple designs yield simple results. In some cases, simple performance features are most desirable, and the bottom of the board may be completely flat, completely convex, or completely concaved. In other cases, more complex design strategies are required in order to meet the demands of the intended rider and wave, and the bottom of the board includes combinations of contours that may be blended together smoothly, or distinctly separated with defined edges. It should be made clear that one design approach is not superior to the other. Rather, it is the astute designer/shaper that understands what design elements are called for under what conditions, and uses any and all available design options to optimize performance.
Flat Bottoms
Excluding the effect of fins, a board that has a completely flat bottom from rail to rail the length of the board relies only on rocker and, to a very limited degree, template features, for lift. Water flows across the bottom of the board along the path of least resistance, until it reaches the rail, where rail shape and volume determine how that water is released out from under the board. The faster the board goes, the higher it planes, and the more release the rails will facilitate. The angle of the plane of the bottom of the board relative to the plane of the water’s surface determines the directions of lift, and rail rocker, being identical to the rocker of the stringer through the middle of the board, is the greatest determining factor of the board’s turning radius, all other design features taken out of the equation (ie. tail width/shape, foil, flex, etc.). The bottom of the board banking against the water through a turn provides some directional stability, but the fin(s) provide the majority of control, preventing the board from spinning out, and redirecting outward centrifugal force into forward motion.
While driving down the line, the path of water along the bottom of the board is, for the most part, from nose to tail, nearly parallel to the stringer. The forward motion of the board as it moves across the face of the wave is responsible for this relative motion of water. But when the plane of the bottom is banked against the water through a turn, the path of water changes… rather than parallel to the stringer, water is deflected diagonally across the bottom of the board. If the bottom of the board is flat, water moves across the board with little disruption or redirection, conserving a great deal of energy, as little is converted into turbulence and drag. In this sense, flat bottoms function in a very predictable and balanced manner, particularly at moderate speeds in medium sized surf. Many shapers agree that flat-bottomed boards are the most efficient and fastest of all bottom designs under certain conditions.
However, flat-bottomed boards can create a bogging sensation at low speeds, as this design lacks any lifting features that can help capture the upward flow of water up the face of the wave and turn that energy into forward speed. Conversely, at high speeds, flat bottom boards can become “slappy,” particularly in choppy conditions. With nothing to cleave through the chop or ventilate the water under the board, the flat bottom runs headlong into surface texture, and at the high speeds generated by large surf, can lead to a sense of uncontrolled bouncing or excessive vibration. Under glassy conditions, this is not an issue, but the design still lacks any control features to help handle high speeds, as the board has a tendency to want to skim across the water’s surface.
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Convex Bottoms
As stated earlier, convex bottoms include a variety of displacement features, all of which lower the stringer relative to the bottom of the rail. Used mostly on longboards, funboards, retro designs, and guns, these features increase bottom rocker along the stringer compared to rail rocker, and lengthen the bottom of the board through the middle. Because nearly all convex bottom features allow the board to sink down deeper into the water than a flat bottom, as the weight of the rider forces the center of the board to settle more deeply into the water, convex bottom features are used sparingly on performance shortboards, where the emphasis is on lift and speed, and responsiveness. The reason why convex bottoms create no lift has to do with the fact that very little of the plane of the bottom is parallel to the plane of the deck, so the opposing force of lift is not straight up under the feet of the rider. Instead, the planes of the bottom on either side of the stringer are angled toward the opposite side of the stringer on the deck side, and so the lifting force is at a tangent to the force of the rider’s weight pushing down on the deck. Working on both sides of the stringer, these opposing tangential forces add a greater sense of stability to these designs than either flat or concaved bottom designs. On many boards, convex features run the length of the board from nose to tail, and these bottoms are sometimes referred to as “hull” bottoms. But more often than not, they are used in combination with other flat and/or concave features to add an element of stability, control, directional projection, or to manipulate rocker.
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Obviously, not all convex bottom features are alike. There are a number of different types of displacement features, and each brings with it its own set of characteristics. The problem with discussing these different features is the fact that different shapers from different eras, or different parts of the world, have different names for the same features. This confusion is due in large part to the culture of surfboard design throughout history (but particularly in the mid to late ‘60s, when design ideas were freely shared within shaping circles), and the tendency of shapers in different parts of the world to simultaneously start working on similar design elements at the same time, but start referring to them by different names, or in some cases, using the same names to describe different designs. For example, vee bottoms have several different varieties – panel, rolled, reverse, spiral, inverted, concaved… and most of them can’t easily be traced back to a single inventor. Such is the case with many design features - there is great debate over who invented what, when, where, and the name it was given at the time. This is exactly the case with the various forms of vee bottoms – shapers in Hawaii, California, Florida and Australia all started working on variations of the vee bottom at about the same time, in an effort to push the performance envelope of boards at the time. Researching the history of the evolution of the vee bottom reveals numerous names like McTavish, Catri, Barnfield, Cole, Hynson, Takayama, Brewer, and others, all arising from a fog of innovation at about the same time.
Panel Vee
The "panel" in the vee refers to the flat sides of the vee which taper down from the stringer, usually all the way to the edge of the rail, in a flat plane. Panel vee is most commonly used in the back third or front third of a board, but may also be used through the middle on some designs. When used in the entry rocker section of the board, the vee helps the board slice through chop much like the hull of a boat. Vee in the entry section also provides some directional stability when current may be in issue, and raises the nose rails slightly. This shortens the length of wetted rail at lower speeds, adds some entry rail rocker for tighter full rail turns, and helps prevent the nose rail from catching when coming around on a top turn. When used in the back third, the vee provides some directional stability and adds rail rocker. The longer and/or deeper the vee, the greater directional stability the board has, and the more rail rocker is added to the tail section of the board. Many people believe that a heavy vee facilitates easy rail-to-rail surfing. However, if the vee in the tail section of the board is deep enough, it adds so much directional stability that the ride becomes sticky and tracky, and the board actually becomes harder to get up onto a rail. Once on a rail, the board will have a tighter turning radius, but there is a considerable loss of sensitivity, particularly on wide-tailed boards, and those that are flat through the middle. Retro fish are perfect examples.
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Panel vee is used extensively on boards designed for large surf, as the vee in the tail brings added control, as the feature brings no lift. Rather, it does the opposite, allowing the tail to penetrate the water deeply, even at speed. Vee usually (but not always) fades to flat behind the trailing fin, blending into the kick of the tail, for release and forgiveness. Vee used through the middle of the board that fades to flat in the tail is commonly referred to by another name...
Reverse Vee
Today, the term "reverse vee" is used very loosely, but generally refers to vee that peaks somewhere between where the entry rocker ends and the leading edge of the front fin(s), and fades to flat in the tail. This forward vee accomplishes many of the same things vee does in other areas of the board, but it is mainly utilized to provide stability and control in boards designed for very large surf. Vee used through the middle of the board flattens the rail rocker through the mid section, but maintains rocker through the middle. Therefore, this design element is not utilized with hard, tight turns in mind. Instead, the focus is on smoothing out turns, maintaining control at high speeds, and providing manageable steerage on an otherwise lengthy and bulky surfboard. Reverse vee is also used in designs ridden by “front footed” surfers – those who put a disproportionate amount of weight on the front, rather than the back foot, and on drive-oriented designs with their wide points forward of center, like retro single fins or boards designed to provide a smooth ride in the tube.
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Spiral Vee
Perhaps the most confusing term in the vee bottom category, the term "spiral vee" most commonly refers to a vee bottom that deepens from around the wide point back, through the fin area, deepening all the way through the end of the board. Shapers experimenting with this "accelerating" vee design were trying to keep the center stringer straighter in the aft section, while adding rocker along the rail starting much further forward that the tail area… closer to the front foot. The design achieved the desired result, and tightened the turning arch, while maintaining down the line speed and drive. When viewed from the side, pintails, diamond tails and other tail shapes with the stringer’s end protruding from the tail block, that were shaped with spiral vee bottoms, would have a rail line who’s bottom edge would have to curve back down to the stringer to meet at the peak of the vee at the board’s end. This re-curved area at the pod made the bottom edge of the rail begin to “spiral” as it move downward and inward toward the stringer, hence the name, "spiral vee."
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Belly
Bellied, or rolled, bottoms are generally rounded convex features. They can be subtly rolled, or highly domed. What sets bellied bottoms apart from other convex bottom shapes are their ability, under certain conditions, to generate a combination of lift and reduced wetted surface, and as a result, higher speeds. Due to the fact that a small region of the dome – it’s peak along the stringer – is nearly flat and parallel to the deck, the lifting force it creates is straight upward, in direct opposition to the force of the rider’s feet pushing down. As the entry rocker of the bottom lifts the board up onto plane, it begins to plane higher and higher, on a narrower and narrower planing surface, eventually planing only on the elongated, narrow peak of the dome down the center of the board… but only if the board is able to reach a high enough speed to do so. This is because a significant amount of lifting force, generated only by entry rocker, is required to hoist the board and rider up and out of the water to plane on the peak of the dome, and this degree of force can only be reached at high speeds. However, once up and planing on the peak of the dome, the reduced wetted surface allows the board to reach even higher speeds, and is the trademark design element of the “hull” shapes perfected by Greg Liddle. His boards are said by devotees to have a “fifth gear” that is only reached in long, fast point surf, where these designs excel and can be exploited.
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This type of bellied dome should not be confused with another specialty design, invented and perfected by Geoff McCoy, called a “loaded dome.” McCoy’s loaded dome design is a softly rounded, pyramid shaped dome, with flattened panels on the sides, front and back. Although it is technically a displacement feature, the front panel actually creates a considerable amount of lift, and a high pressure “pivot point” at the top of the dome for turning. How this loaded dome is blended with rocker, rail, tail width, and other design elements is highly detailed, and a quite sophisticated feature of design.
Rolled Vee
As the name implies, a rolled vee bottom is a vee bottom with some belly curve added to the panels of what would otherwise be a simple panel vee. The roll helps soften the peak of the vee, and brings an added degree of forgiveness to the design. Instead of the panels of the vee acting like the keel of a sailboat, giving the board added directional stability, the roll of the veed panels adds surface area to the bottom, adding drag and allowing slightly more lateral drift. It also softens the bottom edge of the rail, as the bottom of the board is rolled up to the rail’s bottom, facilitating the wrapping of water around the rail. Combined with the ideal fin and rocker setup, the rolled vee bottom becomes ideal for application in the back third or so of noserider longboards. On shorter boards, like fish or retro singles, the rolled vee makes for a smoother ride. Turns seem to have less of a “hard banking” feel to them, common with panel vee bottoms, and instead feel more like a gliding or soaring turn, with less abrupt transitions when going rail to rail.
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Concaved Vee
Imagine a rolled vee with the curves of the rolled panels inverted, and you have a concaved vee. Usually, a panel vee is shaped first, and the desired rail rocker is achieved. Then the panels are gently scoured out to create two concaves, one on either side of the stringer, within the vee. The concaves of the vee change the path of water flowing under the board, particularly along the rail. Instead of spreading water out from the stringer at an angle toward the rail, shedding water out from under the board and releasing it consistently along the raised rail edge, the concaves give the path of water a more nose-to-tail orientation. Water is held longer under the bottom of the board, and the tail planes slightly higher than it would with a simple panel vee. The end result is a bottom shape that has a flatter stringer rocker, curvier rail rocker, and a harder, more drive oriented bottom rail edge created by the higher angle of the bottom as the outside of the concave connects with the rail edge.
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Concave Bottoms
The most definitive and conclusive statement ever made about concave bottoms is this: “Make no generalizations about concaves!” Concaves are likely the most complicated, questioned and debated element of surfboard design theory, yet they are probably the most commonly utilized design feature on modern surfboard bottoms. Concaves come in many shapes and sizes, have a number of effects on performance, and are used on most surfboard types in different variations and combinations. Unfortunately, most shapers have little idea about how concaves work, their knowledge of the design element restricted to feedback from riders, other shapers, personal perceptions, and the utter void of scientific research on the topic that is available, applicable, and comprehendible by general surfing public. With this in mind, most of what we assume can be attributable to concaves has been deduced from what we have indeed learned as a shaping community over the years.
Redirection of Flow
As mentioned earlier, bottoms that incorporate concave designs change the direction of laminar flow of water under the board from angular, diffused flow back and toward the rail away from the stringer, to more channeled flow following the path of the concave. If the perimeter of the concave narrows and curves toward the stringer, as it would from the wide point back, water will encounter resistance against the aft section of the concave, creating a force against the downturned rail edge which pushes not only up (lift), but back and out as well, inducing a degree of drag. But this phenomenon is what gives some riders a sense “bite” or added hold in steep faces or hard turns.
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If water is coming in from both sides of the board, the flow would have to converge, creating an area of high pressure and turbulence in the area of convergence. This convergence of flow is mitigated by the acceleration of tail rocker, but carefully manipulated, can also produce a sense of added lift and projection. In large surf, however, this added lift can become problematic, and can lead to a lack of control some riders refer to as “slippery” or “squirrely.” The likely cause of this sensation is the area of turbulence under the board, somewhere between the rider’s feet. To minimize flow convergence, shapers often turn to the use of double concaves in the aft section, which helps keep the flow from both sides of the template separate. A double concave is simply two parallel concaves on either side of the stringer.
Most modern performance thrusters use some kind of single to double concave setup, where the single concave is shaped first, and the double is shaped within the single. This puts the bottom rail edge lower than the stringer throughout the entire concave array. Typically, the single concave starts 12-18 inches from the tip of the nose, gradually deepening until it reaches its maximum depth somewhere between the wide point of the board and the midpoint between the wide point and the leading edge of the rail fins. The single then gradually fades out to flat or vee behind the trailing edge of the center fin. The double concaves can begin anywhere, but typically begin to fade in at the point where the single concave is deepest. The double concaves are usually deepest near the leading edge of the rail fins, then either quickly fade to flat or vee at the trailing edge of the center fin, or are run right out the tail block, the latter being more common on fish type boards. Many riders report that changing the length of the double concaves changes the feel of the board – lengthening the doubles gives a greater sense of control at speed and added drive. Shortening the doubles gives a greater sense of lift and responsiveness, but a lesser degree of control at speed. This might be explained by the fact that the further forward the doubles extend, the more the flow of water coming through the single concave is kept separated, reducing the turbulence caused by flow convergence as the template narrows.
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Rocker Alterations
Because concaves remove material from the bottom of the board, but leave the rail line untouched, all concaves flatten areas of the bottom of the board, either along the stringer, in the case of single concaves, or on either side of the stringer, in the case of double concaves. Flattening the bottom rocker of the board reduces bottom curvature, creating flatter planing area(s) that can help the board plane earlier at lower speeds, and reach higher top end velocities. The deeper and longer the concave(s), the generally flatter the bottom planing areas will become, relative to rail rocker. Obviously, a deep single concave flattens more area than a double concave alone. The single-to-double concave can add even more flattened area than either the single or the double, if the double concave is shaped into a pre-existing single, further flattening an already flattened curve. In any case, this relative increase in rail rocker line allows the board to maintain its turning radius, while providing flatter planing bottom areas, giving the rider a greater sense of both speed and maneuverability.
Rail Presentation
Often overlooked, and sometimes considered insignificant, concaves change the way the rail is presented to oncoming water flow. The downturned bottom rail edge is considered by some to be more responsive to rail-to-rail pressure changes, as the edge “bites” or “grabs” sooner when the rail is weighted. Compared to flat or convex bottoms, which facilitate release, concaved bottoms help contain flow, conserve energy, and provide a harder rail curve along the bottom of the board that drives the rail deeper into the water due to the change of the plane of the bottom of the board near the rail. Proficient surfers use this feature, along with the concave’s ability to capture flow, as they pump the board for speed, driving off the downturned rail, and projecting off the flex of the board, the flex of the fins, and as they weight and unweight the board. Flat and convex bottoms generally lack the ability to create speed and drive through pumping, so the effect is limited to whatever the rider can get out of flex and fins.
How a concave design changes the plane of the bottom, and how the rail is presented while in trim, during a turn, or while pumping, also affects the water line along the bottom. Due to the curvature of a board’s rocker, there is a water line, usually at some angle, from the inside rail, across the bottom of the board, to the outside rail, that separates the “wetted bottom” from the “un-wetted bottom” under the entry rocker section of the board. Concaves cause this water line to shift slightly back through the concaved areas, as the bottom is lifted compared to the rail. Whether this shift is significant or not is unclear. However, even subtle changes should be considered to have possible affects on board performance when attempting to factor in all possible variables contributing to a more complete and comprehensive theory of bottom design.
Ventilation
A more likely effect of the aft-shifted water line is an increase in ventilation – the introduction of air beneath the board. This concept is widely used in boat hull design to reduce hydrodynamic resistance and to increase speed and efficiency. It is sometimes referred to as “artificial cavitation,” “bottom ventilation,” or “air lubrication,” and commonly seen in boats designed for speed. Because the concaved areas under surfboard bottoms are raised relative to the rail, air entering under the entry rocker section of the board does not quickly diffuse outward toward the rail. Instead, it is held under the board longer as it is funneled through the concaved areas, where it can create a lack of stability, but also may increase speed as the cushioning effect of the air reduces the drag that would otherwise be caused by water. But too much of a good thing can lead to problems, particularly with today’s lightly glassed boards with their ultra-light cores, and particularly if the deeper part of the concave is forward, under or near the rider’s front foot. At high speeds, these highly concaved boards lack the smooth, controlled directional stability of flat bottomed boards, and you can see this in modern performance surfing. Rather than drawing smooth lines, modern performance shortboards, with concaved bottoms, tend to bounce and jitter, even when ridden by some of the world’s best surfers, particularly in large and/or choppy surf. Older shortboards, with heavier cores, heavier glass, or flat-to-vee bottoms, looked and felt much smoother when ridden in the same conditions.
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Channel Bottoms
Like concaves, channel bottoms are designed, in theory, to direct water flow from nose to tail and in doing so, generate more drive and speed. They may also facilitate some ventilation or introduce some boundary layer turbulence, depending on their shape and length. But unlike concaves, channels do not alter rocker in any significant manner. Rather, channels are simply wedge shaped grooves shaped into the existing bottom of the board, whether it be flat, concave or (rarely) convex. The channels are most often toed in at the same angle as the rail fins, and may be uniform in width, or flared slightly from entry to exit. Typically 4 to 8 grooves are shaped into the bottom of the board through the tail section only, although some channel bottoms can begin to fade in at about the middle of the board. The long and deeper the channels, the more their effects are felt. The channels may fade out behind the trailing fin, or may run right off the tail rails and out the tail block. The trailing fin most often sits on the peak created by the two centermost channels, and the rail fins may sit within a channel, or on the edge of a channel.
Most commonly used on boards for small to medium surf, channel bottoms are effective in creating more hold and drive, but at speed have a tendency to become tracky. To compensate for this trackiness would require accelerated rocker, smaller fins, or a narrower tail, all of which would effectively undo what small wave boards are designed to do – plane higher, flatter and faster in weak or small surf. Still, channels do provide excellent hold on steep sections, conserve speed through turns, and add heaps of drive, and so modest accommodations can be made: smaller fins and (because bottom channels, like rail channels, tend to stiffen a board) a touch more rocker are common combinations with this design.
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Bonzer Bottoms
Around 1970, in Oxnard, California, two brothers, Malcolm and Duncan Campbell began to experiment with what they called the Bonzer. It may come as a surprise to many that the Bonzer was a predecessor to both the modern single to double concave and the three-finned thruster with toed and canted side fins. Years before either of those designs arose to popular status, the Campbell brothers were taking the short, wide-tailed, single fin boards of the era, and adding two more side fins, ahead of the center fin. The first Bonzers had flat-to-vee bottoms, but soon evolved into having a shallow single concave forward and two dramatically deep concaves through the tail. The single concave started in the entry rocker section of the board, and narrowed as it approached the wide point, where the double concaves began to fade in. The width of the double concaves did not run all the way out to the rail, but only gently flared from about 3½-4 inches wide along the stringer, to about 4½-5 inches wide through the tail. This gave the entire concave array an hourglass shape. Glassed onto the outside edges of the double concaves sat two long, low aspect, triangular shaped, highly canted fins (about 20 degrees), which essentially become an extension of the concave. These fins were commonly called “side runners.” Because the fins sat on the edge of the Bonzer concaves, they were toed in at the same angle as the concaves’ flared outer edges. The original three fin Bonzer’s triangular side runners had about a 10-inch base.
More than ten years later later, in the early 1980s, the Campbells introduced the Bonzer 5 Fin, which split the single side runners into two smaller, more elliptical or keel shaped fins, which were separated by a narrow channel, or “flute,” with the trailing edge of the outside lead fin slightly overlapping the leading edge of the inside trailing fin. Typically, the 5 Fin version used less cant on the side runners – about 18 degrees or less. The center fins were typically 6-7 inch center box fins. The side runners were about 4¾ and 5¼ inches along the base, with the front set of fins being the larger of the two. This updated version met with great success for more than another ten years, when the addition of the elevated wing was introduced to the design. Part bottom design, part rail design, the wing began low on the rail, but as the tail slowly pulled in, the wing elevated off the bottom edge of the rail, becoming slightly fluted, ending around the trailing edge on the rear side runner. The wind added lift at low speed, bite and hold on steep sections, and pulled the tail template in when on a flatter, faster plane.
Although today’s Bonzers incorporate a number of finely tuned revision, and include a wide array of variations, the purpose of the design remains largely the same. By the Campbells’ own account, the Bonzer was, and remains, “a simple, low tech approach to getting high tech results.” The concaves manage the flow of water under the board very efficiently, channeling water out the back of the board in an effort to create greater speed and drive. The low aspect side runners dip in and out of the water easily, limiting turbulence and drag, while providing superior edge control, increased drive through turns, and blazing down-the-line speed. In addition, the designers contend, the side runners help harness wasted energy by deflecting water coming off the outside rail back, toward the tail, when the board is put on a rail. This rearward deflection water theoretically adds forward momentum to the board, helping the board hold speed through turns. The Campbell brothers contend that, overall, the design is geared toward minimizing entropy – loss of wasted energy that could potentially be conserved and changed into forward motion.
Combination Bottoms
Refinements of traditional bottom designs over the years has resulted in the glaring realization that performance surfing, more often than not, requires the strategic and artful application of a combination of design elements. Outside of personal preference for a “purist” approach, or the design of a specific board for a specific set of conditions, most modern board designs use a variety of design elements that combine concaves with both displacement features and flat sections, that together, allow the rider to put to use a number of features even on a single turn on a single wave. For example, a single board may use a bit of vee in the entry rocker section of the board and single forward concave to help cut through chop and help paddle into a wave. The rider may then drive off a double concave under the back foot through a bottom turn, then set up for a speedy tube section by weighting the front foot over the flattened rocker of forward concave. Coming out of the section, the rider might then pump a few times, building speed by using the concaves together to channel water out the back, then rely on the quick, forgiving release of a flat section behind the trailing fin when coming off the top to finish the ride.
Only through trial and error, continual refinement, and enough water time, can a shaper/surfer begin to get a feel for what element of design does what, and how to combine design features to achieve a desired result.
And that’s what it’s all about.