what's the advantage to the small fin in the middle (trailer? seems like you guys call it) I got my first twinnie about 3 years ago and have been riding it almost exclusively this past spring, but am having an odd relationship with it. There are days when I love it, but recently I've been a bit frustrated and wanting to go back to my retro single fin
The trailer fin acts as a stabilizer to give you a little bit of that thruster feel with the speed and easy turning of a twin. Essentially the board can be ridden as both a thruster and twin finner. As a twin finner you can change the size of the center fin to accommodate the conditions. Included with the board is the shark tooth trailer. You can drop in a slightly larger FCS GS trailer when the surf picks up. Or surf it with a thruster set when the waves get critical. As a twin finner it surfs very different than a thruster. Loose, but not too loose. The larger side fins will hold on your bottom turns, but without the big trailer they will release easy off the top. I surfed the first one I made into the ground in just about every swell this winter. Just changing up the center fin for the conditions.