"The fin system is quite versatile. You can run one, three or four fins if you like. I only run four fins on bigger waves. I find on steeper waves the 4 fin system works better than the 3 fin set-up. Less slip when trying to climb back up on a steeper section. The board has seen quite a bit of use but the three stringers have kept it in one piece."
From http://www.coastalbc.com/surf/boards/309jeffclark.htm