Ive been doing a bit of reading on the bonzer concept, but cant seem to find an explination as to how the fins (in a 3 fin) assist in the venturi effect of the concaves.
Does the toe in and cant assist in guiding the water through the channels ?
the fins and the concaves have to work together…and im just wondering how exaclty they help eachother in producing thrust.
…anyone?
I had “The Bonzer Experience” a little while ago and on a classic Mike Eaton model.
The way the rail fins are canted and towed in the seem and extension of the bottom concaves and make the board ride higher in the water than anything I’ve been on before. The fins on this board were the old clear lexan type a had almost a cushioning effect on the tail. The board had a high & mighty feel to it. I don’t think I could have slowed it down if I’d wanted too.
So simply put – The fins do what you seem to think they do by the questions you ask.
The design is here to stay IMHO. It has a feel unlike anything else.
Mahalo, Rich
Ive been doing a bit of reading on the bonzer concept, but cant seem to find an explination as to how the fins (in a 3 fin) assist in the venturi effect of the concaves.Does the toe in and cant assist in guiding the water through the channels ?
the fins and the concaves have to work together…and im just wondering how exaclty they help eachother in producing thrust.
…anyone?
I’m with Halcyon - the effect is real and pronounced.
The water under a surfboard naturally pushes out to the side. It has a choice - go down or to the side, and the pressure is greater lower (hydrostatic), so the water likes to go to the side. On a turn, the rail fins on the bonzer re-direct water that is headed towards the rail - it is re-directed down and towards the tail. The result is a little bitty bit of thrust and a whole lot of vertical lift.
Concaves play a similar role in keeping water that would otherwise prefer to go across the rail - the concave traps it and pushes it towards the tail instead - more vertical lift.
hth
I thought I would spark the resurgence of this thread because it is a topic that I go over in my mind on a daily basis.
For me, it all started after I met Bill Thrailkill. I had been hanging out with Skip Frye at church, out in the water, and in his shop, taking in every last bit of his knowledge about shaping and theory. I had never ridden a board that I liked as much as my Frye’s. I used to just sit there with my mouth shut and watch every pass, every move, every detail. At one point, he made a comment to me about being the “inspector” because I was nearly eyeball-to-foam from tip to tail on every square inch of a fish he was shaping for someone. Needless to say, I found no flaws… not even a scratch that didn’t match perfectly with the other side. Anyhow, we got to talking about Greenough, flex, Lis, Fish, Geppy, Pendarvis, Pleskunas, and where the “Fish” surfboard was going. At the time he mentioned that the surface hadn’t even been scratched as far as the possibilities of where the design could go. Later, I “inspected” the Frye/Pleskunas “wings” glassed onto the rails of his experimental fish designs, tucked into the quiver of boards on the south wall (left hand wall) of his shop. I thought that the fish was the ultimate in board design and surfing. Then I met Bill Thrailkill. It was like Yin had met Yang, going from Frye to Thrailkill in my mind’s eye of board and fin design theory. Frye was all about flex and all about having those Geppy fins lined up on the pins right at the butt crack. Thrailkill was anti-flex, all about speed out of rigidity, and swore upon a fish design with no butt crack cut out of the tail, but more of a wide square tail, arc tail, or broom tail, driven by two symmetrically foiled fins in Fins Unlimited boxes, glassed 2" off center (the stringer being the center), and working best with rigid high aspect fins foiled on the insides, flat on the outsides, and 6" bases (Thrailkill or Brewer Templates). My mind has been doing flips ever since. I had been lucky enough to spend time learning from masters of both worlds.
I guess I am a sucker for extremes, because I can’t put down my 5’10" and 6’9" Frye Fish that Skip and my wife Melissa surprised me with (one on my birthday, and one at Christmas). Nor can I ever part with my collection of Skip Frye foiled flex fins. And I have shaped more Frye, Lis, Pendarvis, and Pleskunas inspired fish/fish-quad style boards that I can shake a stick at. Yet, I have been taking in everything Bill Thrailkill says (especially after 3 seminars at the Surfing Heritage Foundation and trips to Jim Phillips’ shop) about design, theory, rigid vs. flex, thicker foils vs. thinner foils, hard edges, down rails, venturi effect, etc. and I have gravitated toward trying to find the ultimate speed board for the upper third of the wave face. I have templated out Bill’s “New Shape” Template, the 7’10", the “one board quiver”, the modified Phil Edwards template, the gun curve template, Bills rocker template for the one board quiver, and I have combined what I have learned from him into a 5’10", a 6’0", and a 6’8" with down rails, a hard tail sharp enough to slice yer nuts off, and twin fins in boxes 2" off center (each fin 1" off center)… just like the man taught me. Bill and I worked on these recently and I picked up 4 sets of his custom fins for these boards. I think the man knows what he is talking about. Bill says there is a Venturi effect that occurs between those fins at that precise distance, and I intend to find out exactly what it is that he has discovered.
Hey Dave - I had a similar conversation with Bill. I too have been thinking about trying what you are about to experience. So, please, as The Chipah would say, please, please, please, share your report.
One thing to clarify - from my understanding, and looking at the pictures of Bill’s board - I would say the fins are two inches apart, thus each is one inch off center. Not sure if we are saying the same thing - my read of what you wrote suggests the fins are four inches apart.
Thanks for posting… Anxiously awaiting the ride report in Oregon…
Each fin, one inch off center. Total, two inches apart.
Thanks Bill - Thought I had good notes from our talk, on my end, on a stormy Oregon afternoon.
Still waiting to read the report!
Hey Bill - Do you think it would work somewhat - my current “plan” - with smaller fins? I’ve thought about using my RedX boxes and customizing/making some fins (Side fins have can’t built in, so wouldn’t work well to put 'em facing each other… or would it… make like a steep pyramid “tunnel”…)
Taylor O,
The Red X side fins have 4 degrees of cant built into the root. Since I've only seen Bill's Venturi fin setup once at Cerritos College, I'm not an expert. But, as I recall he had two center fins parallel to and 1" off the stringer. So, if you wanted top see how his setup scales down to a shortboard with Red X you have two options. Use center fins and set the boxes with zero cant. Or, use side fins and cant the boxes in towards the stringer by 4 degrees.
I’m supposed to get the 5’10" back this afternoon… then it’s off to my place for some resin pinlines and my kids’ footprints in acrylic… and finally off to the glosser/polisher…
Then you’ll get your report…