The impact of water pressure forced against a surfboard's surface area which creates acceleration and speed down the line on a wave. This is the most basic way of conveying drive and its instant effect. Examining it more closely, we see that "drive" in surfboard context indicates a couple of variables. First, it's about pressure, more precisely, water pressure operating against a surface. To harness the force, you've got to have a surface for it to work against like a fin. Next, it's about direction and drive is aimed and it's purposeful, not random. Drive doesn't have an complete opposite so much as a corollary, which is drag. Drag is a result of friction between water flow and surface, and it's not completely a bad thing. Without some factors of drag, as without drive, a surfboard would be practically not possible to control. Almost without fail, wherever you create the possibility of drive, you'll also have the possibility of drag. Getting that balance right between the two is the key to great surfboard design. Adding a middle fin brings drive and drag at a central point of a surfboard's tail. The central fins contributes control and direction, providing an core for turns.