Throughout your search, you come across the term “concave”. In reference to what it means in this sense, we really need to clarify what a double concave design is (as it is a step above a single concave design). With a board that sports this type of design, the water will be channeled into two streams throughout the tail and the fins. Not only does this result in faster rides and a looser feel but it also reduces the tracking of a single concave.