Thats a cool fin!
I can imagine a simple way to convert an existing Box fin to this idea but keeping the overall foil of the existing fin by cutting the split from the rear of the fin and inserting the pivot rod from the bottom of the base… worth a try…
" I tried the trailing fin in my shortboard behind a 7.5 inch single, with and without side bites, and just couldn’t get it to feel right 80% of the time and just wentback to the thruster with a smaller center fin set up for the open face squirt and big sweet spot, but still think about putting a small trailer behind that smaller center fin and experimenting. "
…do you have a photo of the shortboard and the fin[s] in question , please ? I would be very keen to see that ! cheers ! ben
Ben,
This is the only photo I found on my laptop with the inline single quad or whatever it should be called.
My board was strapped to the ceiling of my van at the time. It kind of looked right with the shadows, which is why I took the photo.
I tried it with a 7" Cutout fin up front with both fins moved forward in the box and adjusting the distance between them, but it just seemed to work better without the trailer and only in certain parts of the wave did I feel that extra squirt that I got used to when on my longboard with the singletwin.
I found the board with a deeper singlefin in the box kept making me want to move up and trim for speed, rather than keep a foot near the fins and squirt water through them for it. The single was good at powering around whitewater sections with speed, but the thruster was more all around fast and predictable. I kept diggin the single fin into the bottom when duck diving too.
This is my cedar HWS longboard with the inline single Old school rails, The bigger fin is Sapele, white ash and Wenge, the trailer is a Fins Unlimited 3" modified to hang off the end of the box, with some of the base width removed too and refoiled. It was the first fin I modified back after seeing that surfer mag about the inline twin/single twin in the mid 90’s. The bigger fin used to have the tab on the front, but I broke it off, and rebuilt it to the rear giving a little more distance between the fins, which I liked the feel of.
The fin box has been reenforced with carbon fiber roving to spread the load as the box was slightly loose within the epoxy and would seep salt afterward. I built this board 10 years ago and it gets used a lot. I’ve tried it again and again without the trailer, doubting its efficacy, and it is looser, but slower, and during a hard frontside cutback, can spin out. With the trailer the tail is locked in and holds speed through the whole turn and I feel way more in control when trimmed 2/3 or more forward. Forehand bottom turns I feel I get about 25% more projection and often find myself more on my backfoot as the extra degree of acceleration can be unexpected sometimes. Very seldom do I feel this board tracking, and while I could blame the fin setup, I blame the rider instead. Usually it happens after a slower turn on my backhand but sometimes I get stuck in a backhand bottom turn, but that can happen with all my boards regardless of fin setup.
thanks very much for that feedback , mate …most HELPful ! And , did you ever ride the board in the first photo with just the inline single fin setup ??
I did but the board felt too squirrelly, like there was a lack of fin. I borrowed a larger front fin and tried it again but it just didn’t have the drive I was used to from it for faster beachbreak type waves. Perhaps for a slower reef, or if I gave it more time.
The side bites are dual foiled, about 70/30 and pretty flexy. Stiffer side bites with flat insides felt slightly more crisp during a turn, but overall slower with more of a delayed rail to rail response. My preferred thruster side fins are also dual foiled but little flex. First FCS fins I made. I have some more flexible dual foiled side fins but they are lacking with this board
Greg, your straight line fin outlines sure look like glider wing stuff:
Linky (to a very intuitive article about wing outline (or planform)
http://www.spieltek.com/SunbirdSoaring/SoaringArticle/SoaringArticles.htm
Another way of describing your fin setup would be foils in tandem. IIRR, tandem setups tend to have less dynamic drag, although not less wetted surface friction drag than a single fin. Same with staggered arrays, like a biplane with one wing forward of the other- which could be looked at as similar to thruster layouts. And then making the leap to dual fins being like a biplane setup is pretty easy: the top fin of the array ( or the front fin in an inline pair) tends to have a greater angle of attack than the back fin in a steady flow, at least, so the lift of the two fins tends to vary, which might explain what wrcsixeight was talking about as far as where he was feeling the pressure move. Might not be the rider. The two fins are influencing each other’s lift, especially as the angle of the flow of the water to the board changes like in turns vs going straight.
The fluid flow crowd likes to call this circulation…
Bump.
I have nothing new to add. Just bumping because there are quite a few newer members who I think will find this thread interesting. (Aside: you’ll also notice wildy used the F3 boxes for adjustable center fins.)