What’s Actually Happening Under Your Board

Bottom Contours Explained

If you've ever looked at the underside of a surfboard and noticed it isn't flat, that's the bottom contour. It's the shape built into the surfboard and it has a direct effect on how water moves underneath you when you're riding a wave.

Most bottom contours involve some version of a concave: a scooped-out shape that curves inward. The purpose of a concave is to take water flowing in from the nose and direct it along the length of the board’s underside and through the fins at the tail. Done right, this channeling effect creates lift and speed. Additionally, it also affects how your rails grip the wave face and how the board responds when you turn.

It's one of those design elements that most surfers don't think about until they ride a board that feels noticeably different, and then they want to know why.

How a Concave Actually Works

Water flowing under a flat surface just spreads out in all directions whilst a concave channels it. Think of it like a funnel: the scoop collects water coming in from the nose and pushes it out through a more controlled path toward the fins and tail. That directed flow creates lift, which keeps the board riding higher in the water, and speed, which comes from water moving faster through the channel.

Concaves also affect your rail engagement. A well-designed concave helps keep the rail in contact with the wave face when you're turning, which is what gives you grip and control rather than that sliding-around feeling.

Furthermore, the bottom contour isn't always the same from nose to tail. Through the entry and nose it creates early lift, which lets the nose sit flatter without diving when you drop in. Under your feet, in the center, is where the concave is usually deepest. This is the engine of the board, where most of the lift and drive gets generated. Through the tail and fins, the shape controls how your turns feel, whether they're loose and free or locked in and driving.

The Main Types

A single concave is one central channel running down the middle of the board. It maximises lift and down the line speed by creating what shapers call laminar flow; water moving clean and direct from nose to tail. It's the go-to for high-performance surfing and works especially well in smaller, faster waves where you want to get the most drive out of less powerful surf.

A double concave splits the bottom contour into two channels with a raised spine running between them. This concave is mostly used through the tail section of a board. The double concave makes rail-to-rail transitions easier than a single, and gives you more control in turns while still generating some lift, however it's not as fast in a straight line as a single concave board.

The single-to-double is the most common setup on modern performance shortboards. It starts as a single concave under the front foot for speed and drive, then transitions to a double under the back foot for control through turns. It works well across most wave types and conditions, which is why you see it on so many boards. If you're riding a performance shortboard and haven't looked at the bottom, there's a good chance this is what's there.

A vee or convex bottom is the opposite of a concave. This is a raised V shape, usually through the tail section. It doesn't generate lift the same way as a concave, but instead it makes it easier to roll from rail to rail. A vee bottom contour is best used on powerful waves where you don’t need to generate speed but instead easily control it. 

What it Means for the Waves You Surf

For small, punchy beach breaks where you want speed, a single concave does the job well. It's direct and fast, and it gets the most out of weaker waves. If you want a board that can turn hard and handle a range of conditions, from head-high beach break to overhead reef, a single-to-double is where most performance shortboards land. You get the speed through the middle and the control you need when you're driving hard through turns around the back.

The vee is less common in pure performance shapes, but you'll find it more on higher-volume boards or in the tail where a shaper wants to soften the turning feel and make the board more forgiving rail to rail.

Just One Part of the Picture

The bottom contour works alongside rocker, fin setup, tail shape, and rail profile to dictate how a board moves and rides in different kinds of surf. Change one and it affects how all the others feel. 

Most surfers won't need to specify their bottom contour when ordering a board, but knowing what's there and what it's doing helps you understand why one board feels fast and locked in and another feels loose and skatey. 

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