surfer getting out of the water while showing the bottom contours of their surfboard
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The OMBE Guide to Bottom Contours: Surfboard Concave and Convex

The world of surfboard design might confuse newcomers at first look. Let us help you with our detailed guide on surfboard bottom contours.

The bottom contours of your surfboard(s) are probably quite subtle. If you show them to a layperson, some of them might fail to understand where the difference lies. After all, the bottom deck of your surfboard is where it makes contact with the waves, so shouldn’t it be more nuanced than that?

After a bit of surf knowledge and thanks to the guidance of the OMBE method, you should know that surfing is a very subtle sport, even though we like to show off with grand aerial maneuvers and whatnot. So, no matter how subtle differences there are between the bottom contours of different surfboards, they affect your performance on a certain type of wave and your ability to perform well on different kinds of waves to a huge extent.

As we said, it’s where your surfboard establishes its and, subsequently, your first contact with the wave. Your balance, control, speed, and the ability to pull off turns or engage the rail all depend on the nature of that contact. That’s why they’re important, and that’s also why they are actually much more nuanced than you might think at first look.

Now, let’s learn more about their differences and how they affect your performance on the water.

How the Differences in the Surfboard Concave Affect Your Performance

boards with different surfboard concave on a tractor

More often than not, the bottom contours of a surfboard come as a blend of different concaves and convexes in different parts of your surfboard. A board might have a double concave under its nose and a flat part on its chest. Although you might find only flat-bottom boards on the market as well, they’re mostly reserved for beginners who ride small and mushy waves. Otherwise, if you want more nuanced performances and a heightened sense of responsiveness from your board, how different contours are blended plays an important role.

Why? Well, you want a part of your board to direct the water flow on certain waves. For example, a double concave on the nose will cause the water you’re riding over to move sideways, so your board will have more drag passing through the section. 

A single concave, on the other hand, will ensure that the water flows through and under your board, creating a sense of lift and speed. Depending on your speed, lift, and drag preferences, you can choose between the two.

In addition, most of the surfboard designs include a meticulously placed flat part at the bottom regardless of the surfboard type. The reasoning for that is simple: sometimes, you need to plane on the water, neither desiring any lift nor needing any drag. In those cases, engaging the flat part will help you achieve your target.

Different Types of Bottom Contours

surfboards in different colors leaning on a wall

Nowadays, the world of surfboard design is more expansive, diverse, and free-spirited than ever, so you might see all kinds of bottom contours under surfboards. For example, there’s a variation called “belly,” and it’s exactly what it sounds like: your surfboard drinks lots of beer, and it shows through its belly-shaped bottom.

When you’re a competent board shaper who’s making their own surfboards, we can talk about all that in great detail. However, we are only going to focus on three main types of bottom contours and what they’re good for: flats, concaves, and convexes.

Flat Bottom Contours

a flat bottom surfboard lying on sand

As you probably know by now, beginners start surfing on small and mushy waves—waves that are flat themselves. The reason behind that is quite sensible: you can’t just force a person who doesn’t know how to drive to zoom through the city traffic during rush hour. 

They first need to learn the fundamentals and in relative peace of mind. That’s what mushy and flat waves offer to beginners.

In that sense, the flat-bottom soft-top longboard surfboards happen to be the simple car for beginners. They’re stable, buoyant, catch waves easily, and since the ride of beginners doesn’t need to be as nuanced as that of intermediate or advanced surfers, they don’t need any unnecessary complications in terms of surfboard design.

That being said, flat bottom contours are also employed in many high-performance board designs as well. As we said above, you need some planing ability from your board no matter where and how you surf. So, flats are mostly blended into other sorts of bottom contours in a strategic manner. As a result, you’re able to engage the flat parts of your board and generate some planing speed down the surf line.

Concave Bottom Contours

surfboard with double concave on sand

There are two main types of surfboard concaves: single concaves and double concaves. Look at the bottom of a single concave surfboard that lies on its bottom on a table, and you’ll see that the stringer line is a bit raised but nearing the rail line; the board is concave towards its bottom.

Seen from the same angle, on the other hand, double concave bottoms make the shape of a “V”: there are two concaves on either side of the stringer towards the rail line. That’s why the double concave is also referred to as a “V concave.” In contrast to flats, such concave designs increase the overall surface area of your surfboard, as a rail-to-rail curve is inarguably longer than a straight line and creates more lift.

As we briefly mentioned above, a single concave board will let the water go under the board in a laminar flow because its shape doesn’t create any obstacles or drag. Therefore, with the wave completely beneath you, you’ll have more lift and subsequently more speed. This particular aspect also makes engaging the rail a bit easier. Since the force of the wave is preserved under the board, you’ll find surfing on the rail is no problem at all.

The V-shaped stringer of double concaves causes the water flow to go sideways, and since the stringer is the pivot point of the concave, it creates a bit more drag. Drag isn’t always a bad thing either, as it means more balance and control, especially during turns. With a double concave, you’ll be able to master how to delay turns more comfortably.

You might have seen the phrase “single to double concave” in the product descriptions of online surfboard shops, especially of high-performance ones. As you can guess, that’s the option blending the best of both worlds: it provides a more balanced turning radius, great rail-to-rail transition, and the ability to generate speed down the surf line.

However, we should warn you that none of these concave designs are suitable for riding mushy or choppy waves as they emphasize high-performance.

Convex Bottom Contours

Convex bottoms are the exact opposite of concave bottoms in terms of shape. They decrease the surface area, and the stringer line of your surfboard is buried deep into the wave. However, that doesn’t necessarily mean that their operating principle is also the opposite of the concaves. On the contrary, what they offer is also smooth transitions when you’re on the rail.

Then, what’s the difference? Well, telling you that convex bottoms are also referred to as displacement hulls might help you understand the difference. As displacement hulls are employed for more buoyancy on boat designs, a convex bottom will also make your board more buoyant. That’s also why they’re mostly seen on longboards, be it high-performance, soft top, or hybrid.

In addition to its attributes of buoyancy, a convex bottom also promotes stability, making it all the more suitable for longboarding. However, buoyancy and stability shouldn’t deceive you into thinking that the convexes are strictly beginner-friendly. On the contrary—they’re the best friends of big wave surfers and their gun surfboards as well. Without the drag of convexes, the sheer force of big waves would throw many surfers off balance quite quickly.

How Bottom Contours Are Blended in Different Types of Surfboards

How you blend contours determines the performance of your board. So, let’s see what blends are used in the main surfboard shapes you can easily find on the market.

Traditional Longboards

yellow longboard standing vertically on sand

Beginner longboards are mostly flat, as we said above, but some of the traditional longboards have little contour nuances under their tail, nose, or belly. More often than not, the tail will have a convex to simplify and stabilize back foot control.

The chest area will either have a mild convex or flat contour so that the stability of the board is ensured. Moreover, the nose area will entertain a mild concave, preventing nosedives and giving it a little sense of lift.

High-Performance Shortboards

surfer doing an aerial maneuver on a high-performance shortboard

For a good, stylish, and flowing performance, you need to engage the rail quite a lot, but that doesn’t mean you need to sacrifice stability. That’s the most common thinking behind the designs of high-performance shortboards.

Most of them employ a single to double concave design. A single concave under the chest of the wave helps the surfer generate speed without hassle and have some lift during takeoffs, tricks, and maneuvers. However, it blends into a double concave towards the tail and fins to ensure stability and sideways water flow without losing lift.

Some of them might have a flat nose as well. That’s purely because these boards need some paddling power. Considering that shortboards are used on unbroken waves and that those waves are a bit far from the shore, you can understand why that’s a handy attribute.

Hybrid Surfboards

Hybrids are for days when the surf is not apt for your shortboard, but you still want to perform well and even do some rail-surfing. In other words, they’re for a good ride on small and mushy surf.

To that end, although they entertain a single concave like HPSBs, their tails mostly feature a convex contour to add stability. More importantly, though, the convex tail ensures buoyancy and speed on waves that don’t have the energy that you can channel into your ride.

Wrapping Up…

If you’re feeling confused about all these big strides in surfboard design, we understand. How shouldn't we? There are all these different shapes, questions about the surfboard size (if it’s going to lighten you up, we can tell you that it doesn’t matter), and the problem of volume that might throw even the calmest surf coach into a frenzy. Luckily, we aren’t that type, and we have all the surfboard guides you need:

If you want to purchase a new board under the guidance of the best, we can help on that front as well. OMBE head coach Clayton Nienaber is also an accomplished board shaper who worked with legends like Dane Reynolds and Kelly Slater. So, feel free to enroll in our Get the Right Board program!

Written by
Nico Palacios
surf coaching