Surfboard Rail Shapes Explained
There are basically three types of rail shapes: boxy, medium round, or knifey. The shape of the rail, along with its volume, is a major factor in the performance of a board. As water flows around the rail of the board it will follow the contours and create suction or release - or a balance of both. We can determine how a surfboard rail will perform by creating smooth curves for suction and hold into the wave face or abrupt, hard edges for the water to release.
Boxy Rails - a boxy rail is a full volume rail that provides extra floatation and does not penetrate deeply into the wave face. It is somewhat square in shape and therefore forces water to release quickly over the transitions. This can help a board to be looser and feel more “skatey” when used along the middle (front foot area) of the board. Almost all standard shortboards have a very boxy rail toward the tail area around the fin cluster to get quick response and release in the primary turning area of the board. Small wave boards like fish, grovelers, and longboards usually incorporate a boxy rail along the middle to the tail to provide extra floatation for traversing flat sections of a wave.
Medium Round Rails - round, soft, rails are full in shape and provide resistance in turns, but dig into the wave face deeper than boxy rails and creates a nice balance of suction and release in most wave types. Medium round rails have a smooth fluid feel and are the most popular rail shape for most every-day boards. Round rails are great for most types of surf and allow for smooth rail-to-rail surfing, improved control and forgiveness.
Knifey Rails - heavily tapered or pinched rails are more sensitive and easy to sink into a turn. There is less volume in a knifey rail and they can dig deep into a vertical wave face (think Pipeline) and provide a ton of hold and suction as the water wraps and holds the rail contour. A knifey rail is a bit less forgiving than a round rail, but add that extra degree of sensitivity.