On a 10'6": The short 6 inch fin was just the thing Bill was looking for to increase the performance on what he calls his stand up paddle surfboard longboard. Coming from a background of shortboard and thruster fin setups, he felt somewhat restrained leaning the ins and outs of a 2+1 setup with a longer center fin. Thinking it could be the board, he was on verge of putting it up for sale, until he came across a shorty center fin at a local surf shop. After he started running the 6 incher, all thoughts of selling that board quickly vanished leaving Bill stoked. 

On a 9'4": Swapping out a longer center fin for the shorter one made this board loose and faster down the line. In the testing we did stalling on min-bottom turns and cutbacks were almost non-existent as the fin allowed the board to carry the speed through the turns. Although we were only able to test the fin in medium sized surf, we are told that the same holds true in the big waves as well. 

Should everyone swap out their 8" fin for a 5 or 6 inch center fin? We don't think so. With a small center fin, both the longboard and shortboard stand up paddleboards would turn and respond more like a traditional shortboard does, making more use of the rails and surfing off the tail, whereas keeping a longer center fin in there causes the boards to respond more like a traditional longboard with fluid and more pivoting. Is one better that the other or is one going to outperform the other in all circumstances? No way. It all depends on what you're accustomed to as well as your style of surfing. Could it be the answer to your search for increased performance? Yes, but there's only one way to find out, screw on it a try it out. Peace.