20 interesting statemente re quad v tri

[K-man]

surf-h

Way ta go Make waves,create jobs[ding repair]Bet ya send them to freeline

K

[Bryan Jackson]

Willi you are correct in your discussion of how a fin’s flex (whether single, tri or quad) helps create a better hydrodynamic flow and thus aids in turning the board . I was well aware of this fact but in my earlier post I was focusing on that aspect of fin design which contributes to the acceleration felt when coming out of a turn (since that seemed to the focus of the discussion), and it is in this area that I believe you are sadly mistaken .

A flexed fin does indeed impart energy to a board when coming out of a turn and that imparted energy is significant enough to be felt . If you stop to think about it, you will realize that it merely involves basic physics , not mythology .

As I said in my previous post, and as you must no doubt agree, the fin(s) does indeed act like a spring. To flex the fin it takes energy (akin to compressing a spring) and that energy is stored in the fin. When the board comes out of the turn, the fin returns to its natural unflexed state and the stored energy is thus released. There are only two things that can happen to that energy. It can be either:

1) imparted to the surrounding water (i.e., the water is displaced), or

2) imparted to the board, which then accelerates out of the turn.

Regarding the flex characteristics of the shorter wider base tri and quad fins as opposed to a GG style single fin with a longer aspect and a narrower base, all else being equal (that is, they are all composed of the same materials), the shorter fins will be stiffer and not as capable of flexing as much as the single GG style fin (although the combined flex of all three or four fins taken together might be equivalent to that of the GG single fin) .

The limited flexure of the shorter fins (i.e., a multiple fin set-up) as compared to the single fin would thus definitely affect both the way they redirect the water flow and the amount of energy they can impart to the board when coming out the turn .

In addition, when considering drag, the multiple fin set-up will create as much as or possibly even more drag than the single fin, since the combined total surface area and leading/trailing edges of the fins are equal to or greater than the single fin.

Without question a Greenough style single fin is the fastest possible fin set-up possible. The reason why multiple fin set-ups are so popular and prevalent has to do more with the modern style of surfing (call it tricks or maneuvers) which multiple fin set-ups facilitate than with their speed .

Of course, my ideas regarding the different fin flexure capabilities of multi v. single fins are only theoretical speculation on my part but are based upon both physics and personal experimentation. This experimentation involved flexing, by hand, different fin set-ups on different boards and trying to get a feel for how much force was involved and how far I could flex each fin (without damaging the boards involved, of course).

As I suggested in my previous post, it would be quite interesting to do a controlled experiment in a laboratory setting comparing the different fin set-ups for this flex factor and the amount of energy required and/or released . (If someone were to perform this experiment and come up with some hard data that were to disprove my thesis, then and only then would I be willing to change my mind in this regards. )

Also it is hydrodynamics, not aerodynamics, which is the relevant consideration here . I was only referring to airplane wings to illustrate how redirecting the water flow would change the direction of the board (a more apt example might have been the rudder on a boat) and thus aid in turning/maneuvering the board. Although airplane wings can and do flex and impart their energy back into the airplane‘s body, they are not designed with that idea in mind (that is, that it will aid in the airplane‘s performance). Quite the opposite, they are designed to withstand and minimize such stresses .

On the other hand, the Greenough fin was designed with exactly that performance characteristic in mind . It was modeled after the fin of one of the fastest fish in the ocean - the tuna - and the dynamics I discussed (i.e., flexion and the release/imparting of energy) are a well known and studied phenomenon .

And as everyone knows, “You can’t fool Mother Nature” .

[john -]

HEADWAX

the idea of down the line and unweighting put together is perhaps the most straight foward explanation of the feeling in oposition to what ever it is others dont understand about the perception of unweighting

as we read about that DP statement - let it run - it makes sense particulaly if your on a DP board - its working for me

nothin esoteric here mate (im not that clever) - just read the sign and proceed - i'll ground anything into a simple view of the ordinary


yours


dorje

[hart]

For Prof Please consider this possible reality:

The equation goes: Too much rocker gives an easy low risk ride. But too much rocker gives two (and more) things: A more restricted sweet spot and, secondly, fin placement further forward. Fin placement further forward channels us to a tendency to Rail only turns. Having (1) a restricted sweet spot and (2) being restricted to rail turns leads us to the inabilty to change our weight balance longitudinally during the turn and still have drive in our turns.

Being unable to transfer our weight from front to back of the board and maintain drive during the turn (because of too much rocker and it's resulting problems) gives us the unfortunate inability to unweight and harness its bountiful delights. ... and the consequent question mark when someone mentions the concept: unweight.

Dear Wax,

Just as I was getting my head around the feline analogy, you take me to rocker design and fin position. And you know how factual I am when we are describing actualities in board design.

It may be my wrong assumption here, but it seems you are indicating that too much rocker..and a subsequent (too far) forward positioning of the fins will not allow one to "harness bountiful delights...."

1. Rocker

I'm sure you are aware that all professional kneeboard shapers have their blanks glued-up to their own rockers. If you are interested and next time you are in Sydney, I will show you some rocker templates used by such professionals.

Since the 2002 World's my rocker has been straightened on two occasions. I know that it is now flatter than all other contemporary curves in the glue-up section of Dion Chemicals.

2. Fin position

As I know you are talking about David's shapes (and in particularly your newie)..the last time I looked, David's fins are in fact positioned further forward than mine.

Now, as I am loathed to use another question mark here, I must make comment.

Do you believe that fin position and rocker are responsible for "unweighting"..or the subsequent lack of it?

And if Dorje has now mentioned to me that "unweighting" is a perceived idea..then isn't it up to the individual as to whether this action is a desireable one or not?

You see the concept itself isn't the issue here..to me it is a matter of choice. Or in some people's equipment..perhaps a matter of necessity.

Regards as always,

hart

[john -]

good post Hart - clarity is comming on this topic - my fins are foward so i have some considering to do re the latest posts

perception or actuality v design requirements and where does the weight go when unweighting - these are my questions and the difference between letting a board run and driving, based on design/fin placement/roker

is the difference between letting a board run (unweighting) and driving, a perception based on the design

d

[surfhorn]

K-man- Astute observation! In fact, I used to do all of Freeline's repair work at one time! Ah, yes, nothing like a sharp 12" flex fin..........

[hart]

is the difference between letting a board run (unweighting) and driving, a perception based on the design

dorje,

I am not necessarily of the opinion that "letting a board run" can be simply described as 'unweighting'..it means many more things to me. No board should be tethered too tightly by the rider.

And no board should as equally tether the surfer.

That aside, I do agree with the last portion of your post..

Design WILL perceive a style of surfing..and this is a wonderful thing for kneeboarding.

Just as the surfers themselves are highly individualistic..so are the shapers.

Look around and follow the styles and designs that suit the way you want to surf.

DP has a distinctive style..so does Baden. Just as their styles are not that dissimilar..neither is their equipment.

Farrer has a different approach to these guys..and so do I..and I believe that the equipment I surf is different to DP's for that exact reason.

My approach to surfing and shaping is determined by my perception of low / drivey, full-tilt kneeboarding.

And what a wonderful example of that style of surfing is Simon..and not that long ago, Nov..and not that long before him, Crawford.

Am I seeing some kind of trend here?

hart

[willli]

Bryan you have given a good summary of the mythology of flex including tuna and spring loading and conservation of energy. You don't state the most important point which is the greenough fin had high aspect continuous curves as opposed to the 'rudder" designs of the sixties. That skegs have moved away from the deep scythe to more efficient shapes doesn't change the fact that they still use the continuous curves pioneered by GG, and these curves are manipulated to create different responses.
If the deep flexible GG fin was in fact the fastest in the water then tow boards would all be using them but these guys have gone to aluminum to cut down on flex. Of course with them its speed beyond paddle in but the comparison holds. Can't argue with your beliefs so we'll have to hope FCS releases the results of its two million dollar research project on fin dynamics being done in conjunction with the Aus Gov't.
The engineers involved have hinted at breakthroughs already, comparing the current state of fin technology as equivalent to airplanes in the 1930's.
Note this picture of technology also borrowed from tuna:
http://gosurfgear.com/gosurfgearcom/images/mvg2.jpg
Seems there's much more to the fastest swimming fish than the shape of its tail. and I remember skegs copied from the dorsal fins of dolfins, thinking evolution must have gotten nature's surfers right.
So think through what you're saying, that the flexed fin is the bow string and the surfboard the arrow. The relative masses involved argue against that comparison but we're assuming bodies in motion and not at rest. So at what part of the turn does this twang happen? How does it compare to the continuous acceleration of a multi fin setup? Are you riding GG fins exclusively?

[surfhorn]

Hart - Indeed! Kneeboarding is FULL-TILT!!! Its the only way to go!

[K-man]

From hart,

My approach to surfing and shaping is determined by my perception of low / drivey, full-tilt kneeboarding
Very clear,this is ''my style''-No waffling here


from headwax,

And yet some people grasp the unweighting concept easily because it's so much a part of their surfing. This leads us to the corollary: some surfers don't (grasp unweighting idea as easily) because they must have a different way of surfing.
Well said

No value judgements here,just trying to pick through the noodles for that juicy chunk of meat

cheers.

[willli]

Rail turn, aka full on rail turn: a turn initiated at speed by driving into the turn off the front rail and continuing to drive the board through the turn using the front rail as control surface. differs from skeg and tail turn in that there is no weight shift to the rear of the board and no pivot off the skegs or rearward lean. Definitely a "front footed" maneuver and well suited to kneeboarders who use a forward lean driving style and big sweeping turns as the board continues to accelerate without pause.

That should do for a start. The key is the turn is initiated by burying the forward rail and not backing off, often resulting in the rider extended over the water, his face inches away from the surface.

[stemple]

When doing that full rail turn make sure you close your mouth so you will not scoop up some water, Willi!!!

[hart]

To Bill and Syd..

Make sure to keep your minds open..yet your mouths closed.

Otherwise everyone will want to know.

Or at least, learn to swallow.

Special K..

You become more interesting EVERY post you make.

Thanks..

me

[willli]

I figured by trying to define something powerful yet sublime I was going to get a mouthful of criticism. So rather than sink myself deeper, regarding rail turns, think Larry Bertleman.

Edited the rest, too far off topic.