Surfboard Rail Design

SURFBOARD RAIL SHAPE INTRO

Fortunately, the basic physics and hydrodynamic principles that apply to rail shape, or rail profile, are simple and straightforward. There is little mystery about how surfboard rails work, and the application of a few basic points of design can yield consistent results. But this simplicity should not be mistaken for an attempt to understate the design feature’s importance. It should be made clear that even small changes in rail shape and volume can have dramatic effects on how a board performs, and something like a miscalculation in volume, or a misplaced edge, can ultimately become a “make or break” design element in what would otherwise be a finely tuned surf craft. With this in mind, the trick for many shapers, particularly novice shapers, is not what kind of rail to apply to a given design, but the execution of that design during the shaping process itself. And while there are many different techniques used among shapers to cut away foam and foil a perfect rail, there are many more ways to screw things up! But like any functional feature of a surfboard, a basic understanding of how water flows under, around, over, and along a rail is the first step in selecting, then shaping, the perfect rail for the intended wave and rider.

Rail/Wave Interactions

Water flows in almost all directions along a surfboard’s rail. First and foremost, water flows along the rail from nose to tail as the board slices through the water’s surface while in trim or during a turn. In fact, while water may flow along only a small portion of the rail at any given time, namely the back half or third of rail leading into the tail, this lateral flow makes up the primary movement of water along the rail/water interface. Water may flow only under this portion of the rail, or may wrap part way, or in some cases, fully around the rail and onto the deck, depending upon the rail’s shape and volume. Still, the flow of water along the rail from where the rail first engages the wave face, until it releases from under the board out the tail area, must be designed so that turbulence, drag, and release are all controlled and manipulated to attain the desired goal.

Surfboard Design - Hydrodynamics of water flow around a surfboard rail shape

Water also flows upward under the bottom of the rail as water molecules rise up the face of the wave, which creates a lifting force under the rail.

This water interacts with the rail at varying vector angles, depending upon the speed of the board and wave. In sailing, the angle of the wind interacting with the sail is changed by the speed of the moving boat. This combination of relative motions produces what is referred to as “apparent wind,” and may be very different from the “true wind” if the boat is traveling fast enough. A similar condition exists between water flowing along the rail, and the speed of the board and wave. If, for the sake of illustration, we hold the speed of the wave constant, we can see how at higher board speeds, the net vector angle of the upward flow into the rail’s bottom is tilted at a greater angle toward the tail, and becomes closer to parallel with the plane of the rail. At lower board speeds, the net flow is closer to vertical, or more perpendicular to the plane of the rail. However, if we hold board speed constant, we will see an opposite effect when we look at wave speed. At higher wave speeds, the net flow vector upward into the bottom of the rail is more vertical and perpendicular to the plane of the rail – faster wave speeds require water to rise up the face more rapidly. But at lower wave speeds, the net flow is more horizontal along the rail while the board trims, as slower waves require water molecules in the face of the wave to rise more slowly.

Surfboard Design - Speed of a surf board and water wrapping around the rail

Water also flows into the rail, from apex toward the stringer. If the path of a single water molecule is followed as it first interacts with the rail apex, it leads from that point to some other point on the deckside of the rail if it rises, or some other point below the rail apex if it sinks, until it is released. Again, the water flows at some angle along the rail, but still moves inward from the rail apex. Here, the shape of the rail, particularly on the deck side, helps determine the path water will follow as it travels at some angle inward and back along the rail. Water also travels inward from the rail apex as a board moves laterally, or slides, particularly ahead of the widepoint as the tail is pushed ahead of the nose, and the nose is forced to slide into the wave face laterally as the board pivots under the rider’s front foot. During these types of snaps or tail slides, the nose rail is abruptly forced into the wave face, and both the shape and volume of the rail determines, at least to some degree, what happens next – rail shape may force the nose to rise or drop as it slips into the wave face, while rail volume determines the amount of resistance the nose will incur, as a larger volume rail along the nose will not allow the nose to sink as deeply as a thinly foiled nose rail. Similarly, a thicker nose rail will tend to pop back out of the face easier than a thinly foiled nose rail, as the added volume translates into added buoyant force.

The flow of water along, into, and up under the rail, combined with the varying speeds of the wave and board, creates a complicated and dynamic condition that is for all practical purposes in constant flux. Still, among all of this seeming chaos, there can be order. The challenge of the designer-shaper is to create a sense of “equilibrium within the chaos” for the rider, where water flowing in a multitude of directions around the rail can be used deliberately to achieve a desired result… to make the board rise, fall, trim, change speed, release, slide, or even fly. Therefore, when designing a rail for a given board, the shaper must keep in mind the type of wave – is it a thick, ledgy peak, or a thin, peeling wall? Is it a slow, mushy sandbar wave, or firing pointbreak? The shaper also needs to consider the goals of the rider - does the rider want a board that is stable and catches waves easily, or one that is more loose, and suited more for vertical, aerial-oriented surfing? Does the rider want to set a line and walk to the tip, or do hard, driving turns out on the open face?

Surfboard Rail Shape and Water Flow

It is helpful to view rail shapes on a continuum, from hard – having a distinct, hard turn or corner at the bottom of the rail, either created by the shape of the rail, or a bead of resin that is carefully sanded to a sharp edge along the bottom of the rail (or both), to soft – completely rounded, having no edge or corner at all. These two extremes are at the ends of the spectrum for most modern rail shapes, and in the middle there is an infinite continuum of shapes and combinations of shapes that gives the designer/shaper a lot of ideas to play with. To clarify, a rail’s shape can be hard or soft, just as a rail’s edge can be hard or soft – confusing terminology. But it should be understood that a rail can either be hard or soft, depending on its shape (more on this topic in the next few sections), and may or may not have an edge… and that edge may be hard or soft itself.

In addition to hard or soft rail shapes, and hard or soft edges, there is also the matter of rail volume, which becomes another determining factor in a rail’s overall shape and performance. Because of the fact that all rail shapes fit somewhere along an endless continuum of design, it is difficult to draw artificial lines along the spectrum and begin to categorize rail shapes into separate and distinct rail types. Still, it is useful to have some common language to discuss rail shapes, because each change in shape comes with a subsequent change in performance. It’s helpful to recognize that when talking to another shaper or surfer about rail shapes, the conversation is really about rail affect more than about rail shape. But because affects are often relative and hard to quantify, and shapes are easily observable and measurable, most discussion about rail performance defaults to a discussion about rail shape. There are exceptions to this rule, however. Australian surfer/shaper Tom Wegener, who’s work with finless, wooden alaias has made him a master on the topic of rail design (in the absence of fins, the rail becomes the major control feature of the alaia), speaks about rails in less common terms – “suction rails,” “acceleration rails,” and “release rails,” are all terms or phrases of affect that surface when he talks about rail design. While this may be a more accurate way to talk about rail shape and function, most of us need to be able to translate shape into affect in our heads, while we communicate with our language the same concepts but in more quantifiable.

Edged Rails

It’s pretty safe to say that all performance shortboards on the rack today use edges to some degree or another. Even most high performance longboards and retro boards have edges along the bottom of the rail, either in the tail only, or extending up toward the middle of the board, or beyond. By contrast, traditional longboards and noseriders rarely use edges. The function of the hard edge is simple – it releases water, and in doing so, reduces drag and allows the board to plane higher. As stated earlier, flowing water likes to stay attached to curved surfaces due to the coanda effect. The gentler the curve, the longer the flow will stay attached, and the more the water and the surface it is flowing around will pull on each other, holding each other in place. Conversely, edges break the curve, and give the flow of water a point from which to release, rather than hold on.

Surfboard Design - Surfboard Rail Tuck Suction, Control, and water release

If the edge is very hard and sharp the water will release cleanly off the edge, and little if any water will remain attached to the rail above the edge. If the edge is soft (not the rail shape being soft, but the edge itself) and tucked under the apex of the rail, water will release off the edge only if the flow of water is fast enough. The softer the edge, the faster the water must flow to break from the form.

At very low speeds, only a small portion of the water (some would call it the “boundary layer”) will attempt to release from a soft edge, while most of the water will not be disturbed and continue to wrap around the rail. This partial diversion and recombination of flow layers creates a significant degree of turbulent drag along the rail, making this rail profile inefficient in terms of hydrodynamic shape at very slow speeds. Whether this drag is a positive or negative attribute depends on rider preference and the application of the design element. In either case, it takes only a small increase in speed to get to the point where the edge allows the board to plane on the surface of the water. Once up and planing, water ceases to wrap around the rail at all, and the turbulent drag is eliminated. By reducing drag, the edge along the bottom of the rail creates a sort of “lift” (though not in the Bernoullian sense) that results in the board planing faster and higher. In fact, extending an edge further forward will lower the minimum planing speed of any board. All other variables held constant, the board that gets up and planing the fastest will have an edge that extends the furthest toward the nose. If extended all the way to the tip of the nose, an edge will provide a similar kind of “lift,” not only helping to get the board up on plane faster, but preventing the nose rail from catching on boards with lowered entry rocker. The highly influential Mark Richards Twin Fin of the late 1970’s used this extended edge design, and the results were nothing short of a wake-up call for backyard board designers everywhere. From that point on, the use of nose-to-tail edges and hard, down rails (we’ll discuss this in a minute) became a new avenue for experimentation.

50/50 Rails

The term “50/50” refers to the location of the rail apex and the proportion of rail curve above and below the point of the apex. In this type of rail, the apex is in the middle of the rail radius, making the rail very round, gently curved, and its profile nearly symmetrical above and below the apex. This does not mean that the apex is always half way between the plane of the deck and the plane of the bottom, but rather the midpoint of the rail radius itself. Except for some longboards and hull-type shapes, the apex of the 50/50 rail is usually below the halfway point of the deck and bottom planes. This is because the top of the rail radius is smoothly blended into the gradually rising dome of the deck contour, while the bottom of the rail radius flows directly into the flatter bottom of the board. On many longboards and hulls, however, the bottom of the board is also “domed” (more accurately termed rolled or bellied), and so the bottom of the rail must be blended into that convex shape as well, pushing the apex of the rail very close to the midpoint between the planes of the deck and bottom.

In the absence of any edge along the bottom of the 50/50 rail, water has a tendency to flow smoothly and with minimal turbulence around the rail from bottom to top, and along the rail from nose to tail. Full volumed, gently curving, soft 50/50 rails create an exaggerated coanda effect around the rail, giving the rider a sense of amplified “suction.” Lower volumed rails with the same profile generate less of the effect, as the radius is smaller and the turn of the rail harder. Still, with much of the water rising up from under the board finding its way around the rail apex and onto the deck side of the rail, this rail shape becomes very stable, as the symmetrical shape allows the rail to sink deeply into the surface of the water without much resistance. The propensity of this rail shape to find its way deep into the wave face is what causes this sensation of “suction.” Although there is little true suction involved in this scenario, only the water and the rail pulling on each other, it is understandable that the effect can be interpreted as suction, as the rider can get the sensation that the rail is being pulled into the water by some force, and held there until deliberately lifted out as the board is turned.

But this stability does not come without a tradeoff. At higher speeds, this rail shape, whether hard or soft, and in the absence of any discernable edge, has a tendency to continue to “suck” water around the apex, and creates a considerable amount of drag in doing so. Without any release feature to shed water off the rail’s bottom, the round, symmetrical 50/50 rail lowers the top end speed of all boards it is used on, making the application of the rail shape an interesting one – great on boards designed for noseriding, even in the smallest of surf, and on boards designed for the very largest and most powerful surf. The first application helps hold the board firmly in the wave face while trimming from the nose, while the second provides the necessary control through the drag and stability inherent in the design.

Surfboard Down Rails

The term “down rails” refers to rails that have more of the rail’s curve above the apex than below the apex. Many shapers refer to these types of rails as “60/40” rails (60% of the curve above the apex, 40% below), “70/30,” or even “80/20,” depending on how low the apex is. This gives down rails a very different shape than the 50/50 rail. As the apex is lowered, it shortens the amount of bottom rail curve flowing into the plane of the bottom, making a harder rail shape, and elongates the amount of upper rail curve flowing into the deck. This change in proportion makes the rail very asymmetrical, and changes the path of water flowing along and around the rail significantly. Instead of flowing smoothly around the apex and onto the deck as it does around the 50/50 rail, down rails tend to release at least some water from the bottom of the rail as the bottom radius of the rail curve is shortened and tightened. This is due to the fact that rails that have a low apex have a narrower tuck under the rail.

In terms of a rail’s shape, a rail that has a very low apex, and very tight, narrow tuck, would be considered a hard, down rail. In this case, “hard” does not refer to the edge, which may be present or absent on any rail shape, hard or soft, but the actual shape of the rail itself. A narrow tuck means a “harder” turn in the bottom rail profile, and a harder turn for water flowing up from the bottom of the board toward the apex. Some water, particularly at higher speeds, will not be able to remain attached to curve of the narrow-tucked rail, and will release off of the bottom of the rail, reducing both the amount of water flowing around the apex and onto the deck, and its associated drag. This attribute makes the down rail a faster rail, but also less stable in terms of the amount of “suction” it creates. In addition, the narrower tuck of the down rail also makes the effective bottom of the board wider, as less tuck means less foam is taken away in an effort to blend the rail apex into the bottom. For example, lowering the apex of the rail ¼ inch makes the tuck narrower, and the effective bottom planing surface of the board wider, by about the same amount. In this case, lowering the apex and narrowing the tuck on both sides by ¼ inch makes the effective bottom planing surface of the board a total of about ½ wider. The down railed board therefore may have the ride of a board that is lightly wider than it would feel otherwise, making it plane easier, go down the line faster, but be a bit stiffer, than the same board with softer, more symmetrical 50/50 rails.

Eggy, Pinched, and Knifey Surfboard Rails

Rail shapes are not only modified by the location of the apex, but also by their volume. While changing the volume of the rail alone without changing the rail’s shape can be accomplished by simply scaling an existing shape down to the desired volume, a shaper can manipulate both volume and shape using a variety of basic, tried and true rail designs. “Egg” rails, “pinched” rails, and “knife” rails are three commonly used terms to describe a sequence of rail profiles that effectively reduce volume and manipulate release without the use of hard edges. Egg rails have the most volume and least release of the three, and knife rails have the least volume and most release. Pinched rails are a happy medium within the group. All three designs are found mostly on longboards or retro boards, but may also be found on a number of hybrid or specialty boards, and often in combination with other rail shapes and complementary bottom contours, particularly convex bottom designs.

Egg rails resemble the smaller end of an egg, with a soft, tapered profile and round apex. While most egg rails are 50/50 rails, it is not uncommon to see versions of down egg rails on some funboards and retro boards designed for little better performance than their first generation ancestors. The somewhat elliptical shape of the egg rail allows the rail’s profile to blend smoothly into any rounded bottom contour, and gives the board a smooth, gliding ride that is stable at low speeds, but tends to release a bit of water at higher speeds, offering less drag than a completely rounded rail. The reduced volume of this rail also increases rail-to-rail sensitivity to some degree, as the rail is sunk below the water’s surface with greater ease, but the shape still maintains enough volume to be useful in smaller surf. One advantage of the egg rail is its ability to maintain stability in the soup. This is commonly seen with noseriders, who are able to maintain nose trim even through sections of whitewater. Here, the soft, tapered profile if the egg rail offers little resistance to turbulent water flowing into the rail sideways and across the deck. A rail with more volume, even with the apex lowered, would offer much more resistance, and lose stability more easily than the more elliptical shape of the egg rail.

but with even less volume. The pinched rail is used almost exclusively in combination with domed decks, hiding the majority of the board’s volume through the middle. This makes boards with pinched rails much more sensitive than boards with fuller rail profiles, as the reduced volume of the rail, combined with maximized volume along the stringer, creates an imbalance of buoyant forces across the board from rail to rail. In small or slow surf, these low volume rails have a tendency to bog on turns, but in faster, more punchy surf, help release water, and at even higher speeds, when combined with bellied bottoms and the right rocker combinations, give the rider the feeling that the board is actually planing higher along the middle of the board’s length. Planing higher reduces wetted surface area and the drag it creates, making for a very fast board in the right kind of surf. Many hull designs utilize the pinched rail at least at some point along the rail line, if not the whole way, but always in combination with some form of displacement bottom. The pinched rail can be a down rail, a 50/50, or even an “up” rail, with the apex higher than the center of the rail radius. Chined nose rails in the front of many noseriders can be considered a pinched up rail, and create a slightly rounded, yet beveled surface that helps prevent pearling by adding a touch of additional lift directly under the toes. Another distinct advantage the pinched rail offers is its ability to hold a very high line on steep portions of the wave face. Under these conditions, the low volume of the pinched rail penetrates the wave face easily, providing excellent hold and speed, which makes it perform well in the barrel in good sized surf, and hold a high, speedy nose trim line in fast little peelers for those who like the feeling of flying or floating above the surface of the water while out on the tip.

True, traditional knife rails are seldom used today, but were popular during the early years of the shortboard revolution, when the goal of most experimentation was to make a board that was more responsive, could be turned harder, and be maneuvered easily into more critical parts of the wave. Today’s “knife rails” are a much tamer version of the original design, and the term is often used (or misused) to describe any thin rail. But those who know the authentic design will attest to the fact that a true knife rail has an extremely flattened elliptical profile, and was designed with release in mind – and it works well. Water literally jumps off the bottom of a knife rail, as it does a hard edge, but because the rail is so thin, there is little buoyancy to help rebound out of turns. If used through the middle of the board, a design that uses knifey rails when put on a rail must do so with sufficient speed, and must be brought back down on a flat plane coming out of the turn quickly in order to prevent the rail from catching, digging, and completely bogging down. Most shapes that use the knife rail use it only along certain sections of rail, like in the nose or tail, and transition to a rail with a bit more volume through the middle. Effective use of the knife rail is also accompanied by adjustments in rocker, foil and fin configuration that help prevent rail digging, particularly when this thinnest of rail designs is used in the front third of the board.

Beveled or Chined Surfboard Rails

The use of chines – flat or nearly flat bevels along the bottom of the rail – has waxed and waned over the years. And although they are still seen today, particularly around the nose rail of noseriders where they help create lift, they are certainly not the norm, their function either poorly understood or not easily sold to the public. In spite of this, however, they are a proven design element that is still a vital option for those willing to think just a little outside the box, and experiment with something different.

Whether they are flat or slightly rounded… have hard and crisp edges or softly blended ones, all chines do two things: thin the rail’s radius, and raise its apex, both without having to modify the desired bottom or deck contours and general volume of the board. In other words, you don’t have to dome the deck to thin the rail, or belly the bottom to get a high rail apex. This is why most boards with chined rails apply the design feature only through the widest and thickest part of the board. On shortboards, chines usually start a foot or two back from the nose, run through the middle of the board, and fade out toward the tail where the rail has no tuck. On thicker board designs, and on some longboards, the thickness of the board, if carried all the way out to the rail, can create some performance issues as the added volume along the rail increases the rail’s buoyancy and resists being deeply driven into the wave face. On these designs, chines can help loosen up the board, and are sometimes run the entire length of the rail, thinning it from nose to tail, allowing the board’s rail to penetrate the water a little more easily on a hard rail turn. But the shape and width of the chine has to be balanced with all the other design elements, particularly the shape of the rest of the rail, bottom contours, and widepoint location, due to the fact that if the chine is excessively steep and/or wide, the face of the chine ahead of the widepoint will create a planing surface that induces an unbalanced sense of lift along the rail. The chine will actually begin to force the nose of the board out of the water laterally, effectively undoing what was chine was intended to do – create a thinner rail that will allow the rail to sink more deeply into the water. However, some will argue that this phenomenon will have the added benefit of drawing the tail rail deeper, if the rail aft of the widepoint is designed to accommodate that effect – soft and thin.

Finally, if the chine is flat and the edges are hard and crisp, the chine will also create release points for water, preventing it from wrapping around the rail. Along the edge of the chine that meets the bottom of the board, the chine can also help reduce the planning surface of the bottom at higher speeds. But at lower speeds, the two edges add twice the turbulence of a single, tucked edge. If the edges are soft and muted, or the chine itself is slightly rounded, water will flow around the rail a little better, even at moderate speeds, and will require much higher speeds before any release effect is felt, reducing wetted surface. This type of chine thins the rail, and produces less turbulence at lower speeds than the hard-edged chine.

Surfboard Rail Foil and Transitions

For the most part, the foil of the rail – its change in volume as you go nose to tail – should be smooth to minimize turbulent drag and create the feeling of balance and predictability for the rider. Abrupt shape or volume changes along the rail greatly increase drag as the laminar flow along the rail is disrupted and deflected. Viewed from the side, the thickness of the rail should flow, gradually thicker, then gradually thinner, without noticeable transitions between changes in rail volume, apex location, edge, etc., except for the deliberate introduction of bumps, wings or the like, as discussed earlier.

The modern performance shortboard rail is a perfect example of how different rail profiles can be combined along different lengths of rail to achieve a very complex final result that allows the rider to use different sections of rail for different purposes at different times. Particular attention should be paid to the smooth, seamless, nearly unnoticeable transitions between rail profiles as the rail is dissected from tail to nose. This is perhaps one of the greatest tests of a master shaper – the ability to blend dynamic contours that are sometimes very different from one another into a graceful combination of design features that all fit seamlessly together.

While every shaper and surfer has their personal preference and tweak to the “modern railed surfboard,” most modern performance shortboards use the following combinations of rail types and profiles: A hard down or nearly square rail with a crisp, hard, untucked edge from the tip of the tail to the trailing edge of the side fins, where the rail apex begins to gradually bulge from the outside face of the rail. The purpose of this part of the rail is to maximize release and minimize suction and drag. The top of the rail around the tail can be rounded, or for an additional release point along the deck side of the rail and a few more cubic inches of volume, it can be kept square, with a softly rounded top corner.

From there, the bottom edge begins to roll under and become a tucked, hard-edged down rail as it passes the side fins. As the foil of the board begins to thicken, the tucked edge continues to roll under the apex at the same, smooth rate. The hard, tucked edge begins to soften, but still remains defined, ahead of the leading edge of the side fins for about 4” to 6”, where it then begins to become much softer. This is generally a transition area, where incoming water from the widepoint back on the wave-facing side of the board is being cleaved by the edge, some being held below the apex, and some being shed by the thinning rail radius itself. On the opposite side of the board, water is still being released cleanly off the bottom edge, particularly on a turn, where this section of rail may be partly below the water surface, and partly above. This is what makes this transitional area critical to the performance of the board – it must serve several functions at once (and on opposite sides of the board), and must be tuned to work in concert with several other design elements, especially fin setup, foil, and rocker.

Eventually the edge fades into a soft 60/40, then 50/50 rail through the middle and toward the front third of the board, respectively. Through this planing section of the bottom, the rail must be designed for speed and trim, yet still be forgiving enough be driven into any section of the wave, at almost any angle, in a fraction of a second, then recover in the same short period of time. Reaching the entry rocker section of the board, the rail has transitioned into a soft, thin, round radius rail through to the nose’s tip. The foil of the rail can become extremely thin, even pinched toward the tip, as this part of the nose only touches the water when paddling, or during super critical maneuvers that slip the nose into the wave face laterally.

Surfboard Rail Channels

With the rise in popularity and performance of aerial surfing, the addition of rail channels has helped riders hold on to their boards with greater ease. The channel is usually placed along the top of the rail, where the curve of the rail transitions into the deck. When deciding how far in off the rail you would like to place the channel, it is advisable to grab the board by the rails once they are finish shaped, and see where the thumb falls. The channel is usually ¾ to 1 inch wide, and about 3/8 deep. Appropriately placed, the thumb should fit firmly into the groove of the channel, giving the rider a better grip of the board while in the air, often flipping or spinning, which has a tendency to pull the board out of the rider’s hand.

But rail channels are not only for aerialists. In addition, the two grooves add a degree of stiffness and snap resistance to the final product, as the deck, and channels, are most often double glassed, providing greater structural integrity to the board overall. If you don’t see how channels can add to stiffness, try holding a piece of paper straight out by only two corners - the paper droops. Now put a slight curve in the paper and try it again – the paper sticks straight out. The compound curves created by the convex shape deck, plus the concave channel imbedded into it, provide added stiffness and strength, without the addition of any appreciable weight at all.

Surfboard Rail Bands

The first step in designing a surfboard’s rail is to decide what shape and volume of rail will be needed to meet the requirements of the intended rider and wave. As mentioned earlier, there are an infinite number of rail shapes and volumes, and combinations of the two that the shaper can choose from. Yet, there are a few basic rail shapes that can be attained with consistency by measuring and cutting the rail bands to general specifications. However, rail band dimensions change as the thickness of the board changes, so it becomes problematic to prescribe specific dimensions for different rail types. Similarly, the volume and shape of the rail change along the length of any given board, following the foil and rocker of the board, so the dimensions of the rail bands may, and should, change even within a linear inch of rail.

Still, it may be helpful to get an idea of what the relative dimensions are of various rail bands and combinations of bands that, when put together, yield certain basic rail shapes. The following definitions and chart show the dimensions of various rail bands, and the typical rail shapes they produce. For simplicity, the dimensions provided would be the dimensions at the widepoint of a surfboard, assuming a thickness of 2 1/2" at the widepoint. The bands created by the dimensions listed are approximated, and require fine-tuning and modification based on the thickness of the board being shaped, and rider preference. The blending of rail bands and fine-tuning of rail shape and volume is easily done with the electric planer, surform, and coarse sheet abrasives (paper and/or screen), typically in that order. Care should be taken not to tuck the rail along lengths of the rail where a hard edge is desired.

Definitions

Tuck – round or nearly round radius of the bottom of the rail, measured both up from the bottom of the corner of the blank and in from the bottom corner of the blank. The tuck of the rail is the curve from the apex down to where the bottom of the rail blends into the bottom of the board.

Rail Mark – Mark made on the outside, vertical surface of the blank, measured up from the bottom corner of the blank with the blank on the rack, deck side up. Keep in mind where you want your rail apex to be when deciding where to make your marks. It may be helpful to mark your apex first, then shape your tuck, then make your rail and deck marks. This will help you visualize your rail shape and volume a little easier before you make your first rail band cuts.

Deck Marks – Marks made on the deck, measured in from the top corner of the blank and perpendicular to the rail line.

Primary Rail Band - shaped by creating a flat plane connecting the Rail Mark with Deck Mark 1.

Secondary Rail Band – created by connecting the midpoint of the primary band with Deck Mark 2.

Tertiary Rail Band – created by connecting the midpoint of the secondary band with Deck Mark 3. Many rail shapes do not require a tertiary band.

*True 50/50 rails, like those on many classic longboards, require rail bands on the bottom of the board, rather than a simple, curved tuck. For 50/50 rails, flip the blank over, and repeat the same marks and rail band patterns on the bottom of the board as you did on the deck.

**Egg rails require one bottom rail band. To shape this band, make a rail mark 1/2" up from the bottom corner of the rail, and a bottom mark 7/8” in from the bottom corner of the rail. Connect the two marks to create a single flat plane to become your bottom rail band. Blend this band into the curves of the rail and bottom as you do the other bands.

***Pinched or Knifey rails require one bottom rail band. To shape this band, make a rail mark 5/8” up from the bottom corner of the rail, and a bottom mark 1” in from the bottom corner of the rail. Connect the two marks to create a single flat plane to become your bottom rail band. Blend this band into the curves of the rail and bottom as you do the other bands.

One final note on rail bands: For the most part, the vertical surface that remains along the outside of the rail once the tuck is shaped and primary band is cut, determines the overall volume of the rail. It is important that this “band,” which will become the rail apex once the rail is finish shaped, is widest at the widepoint, and tapers smoothly toward the nose and tail. This taper will determine the “foil” of the rail – how the volume of the rail flows from nose to tail.

Continue to Learn More About:

Surfboard Rail Design - Greenlight Surfboard Design Guide