The Bottom of the Surfboard

The underside of the Surfboard. Sounds seedy! There are two parts to note when looking at the reverse side of the board. These are the Bottom Contour of the board and also the Fins (or Fin Boxes for a board with removable fins - don't panic, we will cover this in a bit). There are several different bottom contours to look at, each giving the board different characteristics.

Surfboard Bottom Contours

Here are the main Bottom Contours that you will see on a surfboard, we'll ignore the more experimental shapes. The images below represent a cross-section of the board.

Flat Bottom
As you might guess there is no concave in this type of bottom shape - it is just flat. This type of surfboard bottom contour works well on all types of surfboard and is particularly useful for a 'heavier' surfer.

Single Concave
The Single Concave runs the length of the board and channels water from tip cleanly through the fins. This contour is designed for speed and works well in fast, large clean surf. This shape is does not perform well in messy, lumpy surf and as such is not a good choice for a surfboard you want to use in all round conditions.

Double Concave
The Double Concave is seen on the majority of modern mainstream surfboards and is most likely the bottom concave your board has if you bought it straight off the rack at a surf shop. Generally the board will have a single concave from the nose which will gradually fade into a double concave towards the tail. The single concave towards the nose provides a good planing surface, giving the board drive. The double concave splits the water into two channels through the fins and creates a much looser ride - great for those flowing maneuvers.

Vee
You can see from the image that the lowest point of the board in the water is by the stringer. This low point provides a pivot point and creates easy rail to rail surfing. This shape is normally used towards the tail of the board only - a board with a Vee contour will more than likely have one of the other concaves elsewhere. This is the popular choice for larger wave boards.

Channels
Channels are more of an experimental bottom contour and like the Vee are employed towards the tail of the surfboard. Channels work best in clean surf and are designed to create extra speed.

Fins

The other main feature on the bottom of the board are the fins or fin boxes. Some surfboards have fins permanently glassed on and some will have fin boxes into which fins can be slotted in and secured. Fins are a topic on their own and we look at them separately here.