I was recently given an old 80’s Kennedy thruster, about 6’9" and pretty thick. It is basically a “big guy” shortboard more than a funboard. Looking at the fin setup, the backs of the bases of the front two (4.75" length) fins are a little less than 2.5" from the front of the base of the trailing fin, measured along the stringer. Front two fins are 4.5" base length, trailer 4" base, trailer rear base is 4" from tail. Just looking at the fin setup, the front two fins look like they are too close to the trailing fin. Surfing this board for the second time ever in small, fun waves yesterday, I had an extremely difficult time finding the sweet spot on the board. I could barely pump the board down the line to get speed even with ample wall in front of me. The board surfed really slow. It could be that I am used to more modern bottom contours or something, or maybe that I just can’t surf this board, but I couldnt get any speed at all. I am a total design neophyte, but would moving the two front fins forward help make the sweet spot bigger, or do anything to help me surf it better? If it helps, I surf more off my front foot than my back foot. Any help is appreciated. Thanks, Ian
I’m no expert on tri’s. Your thrusters are 10.5" from the stern. Shouldn’t they be about 13.5" from the stern? I’ve mostly ridden tri fin setups installed by others. My thrusters were farther forward and operated well. The literature I’ve read say that bunching thrusters and center fins causes problems, that bunched tri setups cause boards to bog down, just like you describe. I would re-set the thrusters with their rear bases 13.5" from the stern, measured along the stringer. The rear bases should be 1.25" off the rails. The fins should be be toed in 1/8" to 1/4" each, front to back, and canted 2 to 4 degrees from vertical. More toe-in and cant mean tighter turns, but greater drag. So you choose your ride characteristics. If you want to do the work yourself, I’m sure you can get plenty of advice here at Swaylock’s. Good luck.
I’m no expert on tri’s. Your thrusters are 10.5" from the stern. > Shouldn’t they be about 13.5" from the stern? I’ve mostly ridden tri > fin setups installed by others. My thrusters were farther forward and > operated well. The literature I’ve read say that bunching thrusters and > center fins causes problems, that bunched tri setups cause boards to bog > down, just like you describe.>>> I would re-set the thrusters with their rear bases 13.5" from the > stern, measured along the stringer. The rear bases should be 1.25" > off the rails. The fins should be be toed in 1/8" to 1/4" each, > front to back, and canted 2 to 4 degrees from vertical.>>> More toe-in and cant mean tighter turns, but greater drag. So you choose > your ride characteristics.>>> If you want to do the work yourself, I’m sure you can get plenty of advice > here at Swaylock’s.>>> Good luck. Thanks Noodle Yeah I’m planning on doing the work myself, but Ive never glassed fins on before. Should I use a grinder to cut around fins to get them out, then grind away glass for new position and glass them in? Also, I’m not familiar with fin rope, should I use it or can I just use normal glass around the base. Thank you for any assistance.
Ian - If they are glass fins (not wood or foam core) you might consider leaving em where they are and grinding away some area. I would start with the trailing edges of the forward fins and the leading edge of the back fin. Keep the foil clean and you may be surprised at the results. Too much fin for the conditions makes any board seem slow and sticky.
Yeah I’m planning on doing the work myself, but Ive never glassed fins on > before. Should I use a grinder to cut around fins to get them out, then > grind away glass for new position and glass them in? Also, I’m not > familiar with fin rope, should I use it or can I just use normal glass > around the base.>>> Thank you for any assistance. I’ve only done this one time. I studied up first. It worked. You should use glass rope, but you can pull strands out of glass fabric to make it. Undercut the thrusters with a grinder or hobby tool, leaving the board laminate intact. Grind and sand the old fin locations. Tape the removed fins together. Flatten and equalize the bases. Sand the new fin locations in about 4" x 6" ovals, down to the board glass. Mark and glue the new fins in their new places. I cut styrofoam blocks with the cant angle in place. I taped the fins to the foam, resined the fin bases, and taped the foam to the board while the resin cured. Other Sway posters have posted the value of other fin glues. I ran glass rope down each side of the fins. I flared the rope and taped it to the board where I wanted to cut it when dried. I cut 2" strips and 4" strips of glass, 4 inches longer than the fin bases for laminating the fillets. Lots of glassers use more glass area, even covering the entire fin. I like cut lam edges, so I taped around the oval perimeters before glassing. I layed the glass strips and rope up in one resin pour, but I had trouble working out bubbles. You might want to stage the pours… dope the rope and sand, then dope the fabric. Oh, and the larger cloth should cover the smaller cloth. As the resin kicks, cut the glass fabric perimeter as you pull up the tape. Sand, resin, sand …and you’re done. I may have left something out, if anybody wants to pitch in, feel free. Good luck.
sounds like they are too close together. try your trailer fin at about 3.25" - 3.5" from the tail(trailing edge) and about 11.25- 11.5" from the tail for the trailing edge of your side fins(13.5" up for sides sounds a little too far for a shortboard and more like a longboard thruster measurement, but thats just my op). good luck
sounds like they are too close together. try your trailer fin at about > 3.25" - 3.5" from the tail(trailing edge) and about 11.25- > 11.5" from the tail for the trailing edge of your side > fins(13.5" up for sides sounds a little too far for a shortboard and > more like a longboard thruster measurement, but thats just my op). good > luck Busted! Well then, here’s the reason for my lack of experience with most tri fin setups, DRAG! I like side bites, but not giant thrusters like Ian’s, especially how most builders mount them with 1/4" toe in and 5 degrees of cant. I don’t know how these extemely draggy tri fin setups became accepted as “normal” in the surfboard industry. To me they’re slow. They ALL surf just like Ian describes, screwey! After trying a few thruster setups, I started cutting them down where they were mounted, like John Mellor describes. The one which I remounted, I did so to reset the cant and toe-in to reasonable dimensions. That’s when my boards and my surfing took off. My side bites max out at 3.5", although I’m sure bigger surfers could use bigger thrusters. I still think that 11.5" forward thrusters bunch the fins too tight, even if the whole industry is doing it. Surfing is supposed to be fun, not some trial to see who can overcome their equipment… just my opinion