Here's another person who hasn't given up on flex fins...although I've taken a few years off from them.
John Mel and I were experiementing with 12' flex fins back in the early 1970's. My little 5'0" were so thin and narrow that there was little float and I had to rely on the twang off my bottom turns for speed. I switched over to thrusters in 1980 or so and hung up the flex fin.
But now, after a winter on my 6'0" quad, Ive dropped in a 10" centre box and brought out my collection of flex fins (6" to 12") and am set to start experiementing with various set ups.
Thats why this site is so valuable.......it keeps everyone thinking and pondering on the latest (or oldest) set up. And everyone is an individual with their own particular style.
Hell of a great reason to get up every morning.
20 interesting statemente re quad v tri
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Bryan Jackson
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Willi, everything you’ve said supports the idea of a flex fin returning (at least of some of) its energy to the board 
. Once again, a diver on a spring board is a great example.
Another example from nature, if you will: the cheetah
.
Why is it so damn fast (it can hit 60 miles per hour in a matter of seconds!)? Because when it is running full out its spine acts like spring (or torsion bar if you prefer) which stores and returns the energy that would otherwise be lost to the animal
.
True, if one end of a spring (or torsion bar, which is more or less the same thing in our discussion) is held in a vice that will change the equation, but only in terms of the amount of energy available to be recaptured, not in the overall dynamics of the situation
.
Once again, only one of two things can happen when a flexed fin “springs” back to its original shape. The energy can be used to:
1 - displace the surrounding water (in which case I would imagine the board would do a noticeable side slip), or
2 - be returned to the board, causing it to accelerate.
There are obviously other factors at work with fin dynamics. That is why they are so complex, little understood, and the reason for that 2 million dollar research project you mentioned
.
BTW, changing the analogy to a "bow and arrow" and then trying to discredit me (all that "relative masses" and bodies at rest and motion BS, talk about rambling obfuscation) was a blatant distortion of what I said
. The relevant example I gave was of a tuna fish fin, not a bow and arrow.
In addition, it is a well-known fact that the entire board actually flexes to a certain extent (a hard bottom turn, for example), and this adds to the dynamics of modern surfing as well . Each time a board is stressed the fibers break down just a little bit more. When the fiberglass/resin skin composite eventually breaks down all the way, it loses its 'memory' and the board feels dead 
.
One last thing, you refer to the "continuous acceleration" of multi fin set-ups. Perhaps you would like to expound upon your theories as to how this phenomenon works since, in the Universe according to Willi (no stinkin' superstring theory allowed) and remember flex fins cannot possibly enter into the equation.
. Once again, a diver on a spring board is a great example. Another example from nature, if you will: the cheetah
.Why is it so damn fast (it can hit 60 miles per hour in a matter of seconds!)? Because when it is running full out its spine acts like spring (or torsion bar if you prefer) which stores and returns the energy that would otherwise be lost to the animal
. True, if one end of a spring (or torsion bar, which is more or less the same thing in our discussion) is held in a vice that will change the equation, but only in terms of the amount of energy available to be recaptured, not in the overall dynamics of the situation
.Once again, only one of two things can happen when a flexed fin “springs” back to its original shape. The energy can be used to:
1 - displace the surrounding water (in which case I would imagine the board would do a noticeable side slip), or
2 - be returned to the board, causing it to accelerate.
There are obviously other factors at work with fin dynamics. That is why they are so complex, little understood, and the reason for that 2 million dollar research project you mentioned
. BTW, changing the analogy to a "bow and arrow" and then trying to discredit me (all that "relative masses" and bodies at rest and motion BS, talk about rambling obfuscation) was a blatant distortion of what I said
. The relevant example I gave was of a tuna fish fin, not a bow and arrow. In addition, it is a well-known fact that the entire board actually flexes to a certain extent (a hard bottom turn, for example), and this adds to the dynamics of modern surfing as well
. Each time a board is stressed the fibers break down just a little bit more. When the fiberglass/resin skin composite eventually breaks down all the way, it loses its 'memory' and the board feels dead .One last thing, you refer to the "continuous acceleration" of multi fin set-ups. Perhaps you would like to expound upon your theories as to how this phenomenon works since, in the Universe according to Willi (no stinkin' superstring theory allowed) and remember flex fins cannot possibly enter into the equation.
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willli
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Guess I'll start here:
Displacement: any submerged object displaces water so the fin is already doing that continuously, but you throw in side-slip, a complete herring that presupposes some sort of massive cavitation at the fin creating a pocket of air for it to slip into. we can throw that out cause it makes absolutely no sense.
Leaving the preferred choice: acceleration. So that's how a board accelerates? By flexing its fin? Glad we solved that! But i know you mean ADDED acceleration, boost, twang, rush, jolt of java! Entirely subjective feelings. The skeg didn't relax as the forces on it decreased, it stored em up waiting to kick the board in the tail, as you have postulated. That's why I wanted to know what part of the turn this release happened cos if it wasn't progressive giving back and always achieving optimum balance with the forces on it there's something going on that maybe Scully and Mulder should know about.
As to Thrusters, Quads, Twinfins with say 5deg of toe, yes by definition they are always experiencing some form of angular acceleration while moving through the water, even in a straight line. This creates an inherent instability which when harnessed by the rider permits far greater responsiveness than the long skeg. They are continuously accelerating, even though you can't feel it. Did I mention flex?
Ah HW, Morgans and... trampolines (sung to the tune fromOZ "lions and tigers and bears.. OH MY!") Now thats a treatise to sink yer teeth into! where DO you find the time?
So the diver, in using his weight to deflect the fiberglass board, has no energy imparted to him, the board simply deflects and when he jumps off the cantilever board it vibrates till it uses up the stored energy, which it must give back to gravity and heat. But if the diver walks out to the end, deflecting the board, turns around and walks back, what then? And thats what you're not seeing. The skeg flexes with the force of the water and remains flexed till the force lets up, giving back continuously, like the diver walking back off the board. The preferred state of things in nature is harmony, not hoarding, so the fin doesn't store anything, it continually adjusts to the forces placed on it ie. its flexibleeverything you’ve said supports the idea of a flex fin returning (at least of some of) its energy to the board Surprised . Once again, a diver on a spring board is a great example.
well you've put yourself in a box here, creating a tautology where neither statement is true but you expect the reader to choose ONE and make your argument.Once again, only one of two things can happen when a flexed fin “springs” back to its original shape. The energy can be used to:
1 - displace the surrounding water (in which case I would imagine the board would do a noticeable side slip), or
2 - be returned to the board, causing it to accelerate.
Displacement: any submerged object displaces water so the fin is already doing that continuously, but you throw in side-slip, a complete herring that presupposes some sort of massive cavitation at the fin creating a pocket of air for it to slip into. we can throw that out cause it makes absolutely no sense.
Leaving the preferred choice: acceleration. So that's how a board accelerates? By flexing its fin? Glad we solved that! But i know you mean ADDED acceleration, boost, twang, rush, jolt of java! Entirely subjective feelings. The skeg didn't relax as the forces on it decreased, it stored em up waiting to kick the board in the tail, as you have postulated. That's why I wanted to know what part of the turn this release happened cos if it wasn't progressive giving back and always achieving optimum balance with the forces on it there's something going on that maybe Scully and Mulder should know about.
As to Thrusters, Quads, Twinfins with say 5deg of toe, yes by definition they are always experiencing some form of angular acceleration while moving through the water, even in a straight line. This creates an inherent instability which when harnessed by the rider permits far greater responsiveness than the long skeg. They are continuously accelerating, even though you can't feel it. Did I mention flex?
Ah HW, Morgans and... trampolines (sung to the tune fromOZ "lions and tigers and bears.. OH MY!") Now thats a treatise to sink yer teeth into! where DO you find the time?
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Eric Carson
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Bryan Jackson
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Well, Willi, there you go again (to steal a qoute from a recently deceased statesman 
). You claim that I've put myself "in a box...creating a tautology where neither statement is true..."
Then pray tell, dear Willi, exactly where does the energy stored in the flexed fin go to (of course, that is assuming you even agree that there is energy stored in that flexed fin ). Talk about a case for Scully and Mulder. It could be titled: 'The Mysterious Case of the Disappearing Fin Energy!' (OK, the title could use some work, but the question remains). So please fill us in on the details .
And regarding your "continuous acceleration", do you mean that the board would accelerate without limit, to an infinite speed perhaps
? Impossible! In fact, the fastest a (paddled-in) board can possibly go is in a free fall down the face of the wave (which is, of course, usually not too much fun) !
A board with toed-in fins must be constantly turned, otherwise it decelerates due to the drag created by the toed-in fins. This is a well-known fact
. (Note one exception: in a powerful, hollow wave where the wave has more than enough juice to drive the board in a straight line, the prime consideration is the rider's ability to maintain his or her position in the power pocket ).
As for the diver on a springboard, the diver on the board jumps onto the end, thereby temporarily increasing his or her weight upon that board, which then flexes and returns the energy to the diver "springing" (there's that pesky word again which seems to cause you so much consternation) back up into the air
.
The same thing happens with a flex fin. When the board hits the bottom turn the force upon the board (it's "weight" also known as G forces) is increased. This is harnessed, in part, and returned by the flexed fin .
I have attempted to give a cogent explanation of (some) of the forces involved in fin dynamics, whereas it seems that you continue on yet another rambling rant attempting to obfuscate and confuse the issue, but which only serves to reinforce my thesis (which I admit could be wrong, but at least it makes sense ).
I can see why this debate is giving others headaches .
P.S. Sorry, I didn't mean to ignore you, Surfhorn. Your post was a nice contribution to the discussion. I would very much like to hear some more of your thoughts on this subject and/or the results of your experiments. What forces do you think are at play with the single flex fin?
). You claim that I've put myself "in a box...creating a tautology where neither statement is true..."Then pray tell, dear Willi, exactly where does the energy stored in the flexed fin go to (of course, that is assuming you even agree that there is energy stored in that flexed fin
). Talk about a case for Scully and Mulder. It could be titled: 'The Mysterious Case of the Disappearing Fin Energy!' (OK, the title could use some work, but the question remains). So please fill us in on the details .And regarding your "continuous acceleration", do you mean that the board would accelerate without limit, to an infinite speed perhaps
? Impossible! In fact, the fastest a (paddled-in) board can possibly go is in a free fall down the face of the wave (which is, of course, usually not too much fun) ! A board with toed-in fins must be constantly turned, otherwise it decelerates due to the drag created by the toed-in fins. This is a well-known fact
. (Note one exception: in a powerful, hollow wave where the wave has more than enough juice to drive the board in a straight line, the prime consideration is the rider's ability to maintain his or her position in the power pocket ).As for the diver on a springboard, the diver on the board jumps onto the end, thereby temporarily increasing his or her weight upon that board, which then flexes and returns the energy to the diver "springing" (there's that pesky word again which seems to cause you so much consternation) back up into the air
.The same thing happens with a flex fin. When the board hits the bottom turn the force upon the board (it's "weight" also known as G forces) is increased. This is harnessed, in part, and returned by the flexed fin
. I have attempted to give a cogent explanation of (some) of the forces involved in fin dynamics, whereas it seems that you continue on yet another rambling rant attempting to obfuscate and confuse the issue, but which only serves to reinforce my thesis (which I admit could be wrong, but at least it makes sense
).I can see why this debate is giving others headaches
.P.S. Sorry, I didn't mean to ignore you, Surfhorn. Your post was a nice contribution to the discussion. I would very much like to hear some more of your thoughts on this subject and/or the results of your experiments. What forces do you think are at play with the single flex fin?
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Beeline2.0
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willli
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This will be my last post on this subject. Bryan you get the last word.
Now I see the problem. you're confused about acceleration. If you can digest the mini-lesson by Beeline above then
here's a good problem to get you started on the right path:
A satellite in geosync orbit always appears to be in the same place in relation to the rotating earth. It is moving at a fixed speed yet always accelerating. It has somehow balanced the acceleration of gravity while at the same time, appears to the observer on earth to never move. How is this possible if by definition (Brian's) acceleration means your speed must ever increase? And your senses ( sight, good TV reception) tell you it never moves?
Ocean waves are far more complicated than simple gravity. You have this curved energy surface moving through a gravity field and viscous medium and you have this object (surfer and board) moving along with it, yet at the same time dashing about, and all the energy must be conserved (accounted for) including that added by the surfer himself.
This genius comes along, (call him Greenough), seeking harmony with the forces at work so he introduces flex into the equation. He wants a craft that fits itself to the wave and has the capacity to constantly adjust. His thinking eventually takes him away from semi-rigid plastics toward even more pliable surfaces: mats.
You took one maneuver in surfing (bottom turn), added in a flexible fin (part of the very board its supposedly trading energy with) and made all sorts of suppositions based on grade school science, then tried to sell it as fact. I'm not buying. But I can imagine the original conversations that took place over 30 years ago. Why? Cause I heard them.
“Dude ya gotta try this new fin! Like wow man! Ya hit the bottom and BOING ! Board springs ahead Dude. Its like ALIVE man. Totally freaky! Must tap into the cosmic karma of the wave Dude! Guy that made it rides a board you can seethru! How freaky is that Dude! Gotta go man. My lady scored some righteous stuff!”
IF FCS releases what it learns I'll try and understand the way they framed the problem, work the equations,see what variables they included. Maybe the senses will be vindicated. Going retro is always fun. Some of us need nostalgia to verify ourselves. Hell for 99.99% of the surfing world kneeboarding itself is retro. My guess is that deep flexible glass-on is only going to deliver on a nice long point wave. I’d steer clear of fast shorebreak. But I can ride my thruster anywhere. And over 30 years ago fresh out of college physics class and up to my mazuza in head spinning math the dude says:
"Dude ya can't QUESTION this stuff. Its not like what's goin on is ROCKET science. It don't matter HOW it works. Just go surf. If ya like it, cool! Just don't mess with it man. Ya gotta have someplace to RELAX and have a good time. Look at it man. Its GOING OFF! I"M STOKED! Lets surf"
Thank god one thing never changes.
Now I see the problem. you're confused about acceleration. If you can digest the mini-lesson by Beeline above then
here's a good problem to get you started on the right path:
A satellite in geosync orbit always appears to be in the same place in relation to the rotating earth. It is moving at a fixed speed yet always accelerating. It has somehow balanced the acceleration of gravity while at the same time, appears to the observer on earth to never move. How is this possible if by definition (Brian's) acceleration means your speed must ever increase? And your senses ( sight, good TV reception) tell you it never moves?
Ocean waves are far more complicated than simple gravity. You have this curved energy surface moving through a gravity field and viscous medium and you have this object (surfer and board) moving along with it, yet at the same time dashing about, and all the energy must be conserved (accounted for) including that added by the surfer himself.
This genius comes along, (call him Greenough), seeking harmony with the forces at work so he introduces flex into the equation. He wants a craft that fits itself to the wave and has the capacity to constantly adjust. His thinking eventually takes him away from semi-rigid plastics toward even more pliable surfaces: mats.
You took one maneuver in surfing (bottom turn), added in a flexible fin (part of the very board its supposedly trading energy with) and made all sorts of suppositions based on grade school science, then tried to sell it as fact. I'm not buying. But I can imagine the original conversations that took place over 30 years ago. Why? Cause I heard them.
“Dude ya gotta try this new fin! Like wow man! Ya hit the bottom and BOING ! Board springs ahead Dude. Its like ALIVE man. Totally freaky! Must tap into the cosmic karma of the wave Dude! Guy that made it rides a board you can seethru! How freaky is that Dude! Gotta go man. My lady scored some righteous stuff!”
IF FCS releases what it learns I'll try and understand the way they framed the problem, work the equations,see what variables they included. Maybe the senses will be vindicated. Going retro is always fun. Some of us need nostalgia to verify ourselves. Hell for 99.99% of the surfing world kneeboarding itself is retro. My guess is that deep flexible glass-on is only going to deliver on a nice long point wave. I’d steer clear of fast shorebreak. But I can ride my thruster anywhere. And over 30 years ago fresh out of college physics class and up to my mazuza in head spinning math the dude says:
"Dude ya can't QUESTION this stuff. Its not like what's goin on is ROCKET science. It don't matter HOW it works. Just go surf. If ya like it, cool! Just don't mess with it man. Ya gotta have someplace to RELAX and have a good time. Look at it man. Its GOING OFF! I"M STOKED! Lets surf"
Thank god one thing never changes.
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Bryan Jackson
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Beeline,
Tanks for the physics lesson but I was already well aware of the difference between the everyday meaning of "acceleration" and the more precise scientific definition . And you really haven't solved the conundrum other than stating the obvious, that is that all surfboards experience acceleration (and deceleration), albeit under different circumstances 
.
Regardless, my statement that a (paddle-in) surfboard cannot go any faster than it would in a freefall down the face of the wave is 100% correct, since (once the wave has been caught) gravity and, of course the energy (e.g., forward motion) of the wave (which is still slower than a body in freefall through the air) are the only outside forces acting to propel the board and rider (who can, of course, take advantage of these forces but add nothing to them) . Period! End of story!
You can do all the fancy turns you want and it may seem like you are going faster but that is an illusion . The fastest speed possibly attained will still be in a straight line minimizing drag (can I get a round of applause for the single fin ). You may "snap" a turn but all you have done is change direction, not increase your speed . Hence the need to "pump" thrusters et al other toed-in multifin set-ups to, among other things, minimize the drag they would otherwise induce when traveling in a straight line . Of course, surfing is not just about traveling as fast as possible in a straight line, but sometimes that is an extremely critical factor .
You also mention the problem with single/twin fins losing their speed after a manuever
. That may be true if you are trying to do a thruster-like manuever. Therefore, the thing to do is to surf them as a single/twin fin, not a thruster. Duh!
Willi,
You asked for a specific instance when the force of the flex fin might come into play and I gave you one (hard bottom turn), then you turn around and dismiss my example because it is a limited circumstance . No way to win the argument when up against such disingenuousness .
You also seem to be hung up the drug addled 60's and use that as a way to put down my ideas. How sad Since you say you were there perhaps you have suffered permanent brain damage as a result !
Tanks for the physics lesson but I was already well aware of the difference between the everyday meaning of "acceleration" and the more precise scientific definition
. And you really haven't solved the conundrum other than stating the obvious, that is that all surfboards experience acceleration (and deceleration), albeit under different circumstances .Regardless, my statement that a (paddle-in) surfboard cannot go any faster than it would in a freefall down the face of the wave is 100% correct, since (once the wave has been caught) gravity and, of course the energy (e.g., forward motion) of the wave (which is still slower than a body in freefall through the air) are the only outside forces acting to propel the board and rider (who can, of course, take advantage of these forces but add nothing to them)
. Period! End of story! You can do all the fancy turns you want and it may seem like you are going faster but that is an illusion
. The fastest speed possibly attained will still be in a straight line minimizing drag (can I get a round of applause for the single fin ). You may "snap" a turn but all you have done is change direction, not increase your speed . Hence the need to "pump" thrusters et al other toed-in multifin set-ups to, among other things, minimize the drag they would otherwise induce when traveling in a straight line . Of course, surfing is not just about traveling as fast as possible in a straight line, but sometimes that is an extremely critical factor . You also mention the problem with single/twin fins losing their speed after a manuever
. That may be true if you are trying to do a thruster-like manuever. Therefore, the thing to do is to surf them as a single/twin fin, not a thruster. Duh! Willi,
You asked for a specific instance when the force of the flex fin might come into play and I gave you one (hard bottom turn), then you turn around and dismiss my example because it is a limited circumstance
. No way to win the argument when up against such disingenuousness .You also seem to be hung up the drug addled 60's and use that as a way to put down my ideas. How sad
Since you say you were there perhaps you have suffered permanent brain damage as a result !-
fooj
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I am no physicist, but what if you return to the top of a wave already with speed (ie, up and riding) then drop back down, the acceleration of gravity would apply to the velocity which you already have and increase it, = faster than freefall. Correct? This is assuming that no wave is large enough to allow anyone to achieve terminal velocity during freefall.Regardless, my statement that a (paddle-in) surfboard cannot go any faster than it would in a freefall down the face of the wave is 100% correct, since (once the wave has been caught) gravity and, of course the energy (e.g., forward motion) of the wave (which is still slower than a body in freefall through the air) are the only outside forces acting to propel the board and rider (who can, of course, take advantage of these forces but add nothing to them) Surprised . Period! End of story!
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Bryan Jackson
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. Once you reach the top of your trajectory up the wave (zenith) your vertical velocity (speed) is exactly zero.-
fooj
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Bryan, told you I wasn't a physicist. I still believe you can go faster than freefall on a wave, just don't have the scholastic backing to explain it. Perhaps it has something to do with the fact that most of us don't ride straight up/straight down? I'm sidelined on this one, should have kept my damn mouth shut!
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Bryan Jackson
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Jfooj, no problem. Hope you didn't take my response as unwarranted criticism . Only trying to explain why your idea didn't "fly".
The feeling that you are going faster than than it would be possible to go in a freefall situation is purely a psychological phenomenon .
Without going into too much detail (and at the risk of exposing myself to a scathing rebuttal by the likes of Beeline or Willi ), an open ocean swell rises up when it feels the drag of the sea bottom upon entering shallower water. When the height of the wave exceeds that which can be supported by the energy of the swell, it falls forward . Whether it is a gentle spilling wave or a critically hollow wave (or something in between) depends upon how fast the open ocean swell is traveling and how abruptly shallow the bottom doth become (offshore/onshore winds can also play an important role in either holding up or blowing over the wave) .
Bottom line: Even the awesome falling lip of a wave as hollow and throwing as Pipeline or Te'ahupo'o is in a freefall situation .
. Only trying to explain why your idea didn't "fly".The feeling that you are going faster than than it would be possible to go in a freefall situation is purely a psychological phenomenon
.Without going into too much detail (and at the risk of exposing myself to a scathing rebuttal by the likes of Beeline or Willi
), an open ocean swell rises up when it feels the drag of the sea bottom upon entering shallower water. When the height of the wave exceeds that which can be supported by the energy of the swell, it falls forward . Whether it is a gentle spilling wave or a critically hollow wave (or something in between) depends upon how fast the open ocean swell is traveling and how abruptly shallow the bottom doth become (offshore/onshore winds can also play an important role in either holding up or blowing over the wave) .Bottom line: Even the awesome falling lip of a wave as hollow and throwing as Pipeline or Te'ahupo'o is in a freefall situation
.