Okay, if you choose a bat tail, a bat tail usually runs on a four fin design. That's what's the first design with the bat tail. Basically, it's very similar to your swallow tail outline, with the straighter line in the tail, which is giving you projection. And then, it curves down and then back up, which gives you another, it gives you release and then another little bit of projection in your turn. The water flow will come down, giving you projection, releasing and then, giving you another little bit of projection in holding into the wave.
Again now, bat tails are usually run with the four fin set up because of the straighter rail lines and the turning behind it. The bat tail, is great for small surf, in medium surf and again, in the bigger surf with the four fin design. That's your bat tail.