is some of the added drive given to a board by the flex in the fin lost as it it unloads the energy sideways trying to move the board sideways? i know flexible fins work, but could they be more efficient if the tip of the fin did not move laterally in relation to the base of the fin, and instead the trailing edge flexed side to side, with the most movement being in the middle of the fin.
it seems to me that this might be a more accurate re-creation of how a fish’s fin works/moves.
i imagine (and am probably wrong) that the effect could kind of be achieved by the entire leading edge being unflexible and the rest of the fin very flexible.
my skills and equipment mean i won’t be able to try this, at least in the short term.
i would be honoured by any response to this probably incomprehensible post.
tom,
beginner shaper in south wales (the old south wales)
oh, is that how that halcyon guys weird looking fins work?
do you think that your fins produce the same results as the fin i described, they look pretty intersting.
i can see how side-bites, correctly toed in would help redirect the energy from a normal flex fin. because of the action of the fin on your site, would you say that side fins are unneccesary with such a setup on a long board ( where the side fins have little toe.)
on re-evaluation of my idea i think a twisting fin would eliminate the problems and create the effect i visualise.
The rider affect board drive out of turns much more than any fin config ever possibly could.
And if the fin config gives nice drive, there are moments when the rider needs LESS drive…to go vert, to hit the lip, to snap, so fins that develop great drive are not necessary.
Ok, Here’s the foil/flex picture of my fin concept in a kernel:
As water leaves any surface it tends to spiral, so if water likes to spiral why not go with the flow and shape the fin in a spiral (helical) form from the base/leading edge to the the tip/trailing edge? That’s what I do on rail fins. As a result while the fin is growing out of the board the cant and toe-in both increase subtly. This tends to release water more smoothly during fin loading. It also encourages better engagement with laminar flow, which some surfers who shall go unnamed don’t like. On the high pressure side of the fin the trailing edge has the concave relieved to mimumize drag and maximize release much as keeping the draft (deep part of the loaded side) in a sail more toward the luff than the leech, which produces a more powerful configuration on a given surface area.
As to flex: The thickness in the fin is toward the base of course and tapers toward the tip, thus the flex pattern of the fin is simply one where tip is the springiest part of the fin. Recoil speed figures into fin power big time and the slower the recoil the more the fin will suit a slower responding board. This is addressed by foil thicknesses and composite construction techniques. Quick recoil fins are for high performance fast responding boards. Some boards require completely rigid fins. Depending on board configuration fin flex can either be performance enhancing or destroying ~
Think of it like this: Ballet slippers with steel taps wouldn’t do at all, at the same time taps with rubber soles would be a drag.
In the end it’s all about grip and release and melding the two appropriately for a given craft.
do you think that your fins produce the same results as the fin i described, they look pretty intersting.
i can see how side-bites, correctly toed in would help redirect the energy from a normal flex fin. because of the action of the fin on your site, would you say that side fins are unneccesary with such a setup on a long board ( where the side fins have little toe.)
on re-evaluation of my idea i think a twisting fin would eliminate the problems and create the effect i visualise.
thanks for the reply,
tom
My fins work better in singles designed for use with flex fins than the flex fins do…
But there is a good reason for rail fins…in a turn, the water flow near the inside rail is the fastest of anyplace on the board. You put the fin there to get the most turning power. There is no substitute. The problem with fixed rail fins is that you cannot get rid of the problematic outside rail fin which is quite a drag, especially on longboards where it is tougher to angle hard enough to go into a two fin turn…
Really, a merging of the two concepts is the solution…a fin that rotates in toe-in and toe-out, so that an outside rail fin is not in the way when you turn, and both rail fins are not snowplowing when you want to go straight.
