Discussing Roy's surfboard designs.

[zaGaffer]

Those are tubercules, which are based on those found on humpback whale fins. There's been extensive research done on them, they greatly increase angle of attack capability, reduce drag and increase lift. On wind turbines they are achieving a 30% increase in overall efficiency ( that's from memory, it might be greater). The tubercules work by introducing vorteces, these prevent flow separation on the low pressure side of the fin. The whale bump fins certainly have a much more powerful feel under load.

A search for Dr Frank Fish will bring up some articles.

Thanks Roy

[LBCrew]

So... what does the "torsion" in "flexible torsion" mean, since you're saying (and I agree) that torsional flex is limited while horizontal flex is desirable? Does causing the board to flex by weighting/unweighting help generate speed through storing and releasing energy?

I disagree that gravitational potential energy provides the vast majority of surfboards' forward kinetic energy. Granted, for longboards it may be greater, and more significant than shortboards, but there's no hard data that I'm aware of to support either argument. Regardless... can you explain how heavier boards/riders accelerate at the same rate as lighter boards/riders? It's my understanding that more energy is required to overcome the inertia of a motionless object if it has greater mass. Also, can you explain how lowering a surfboard's center of gravity will make it ride smoother... particularly if it is of equal weight? I would suggest it is the weight and not the location of it's center of mass.

[Roy Stuart]

So... what does the "torsion" in "flexible torsion" mean,

http://en.wikipedia.org/wiki/Torsion_box

since you're saying (and I agree) that torsional flex is limited while horizontal flex is desirable? Does causing the board to flex by weighting/unweighting help generate speed through storing and releasing energy?

I believe so.

I disagree that gravitational potential energy provides the vast majority of surfboards' forward kinetic energy.

It does though, it's a simple matter of physics.

Granted, for longboards it may be greater, and more significant than shortboards, but there's no hard data that I'm aware of to support either argument.

It can be calculated for any given situation. The amount of physical energy which the rider can apply is a very small percentage of the overall energy equation.

Regardless... can you explain how heavier boards/riders accelerate at the same rate as lighter boards/riders? It's my understanding that more energy is required to overcome the inertia of a motionless object if it has greater mass.

Physics determines that gravitational potential energy is proportional to mass, and it is the main means of propulsion.

Rider energy is not proportional to surfboard mass but is a small part of the equation.

Also, can you explain how lowering a surfboard's center of gravity will make it ride smoother... particularly if it is of equal weight?

I would suggest it is the weight and not the location of it's center of mass.

The magnitude of the mass and its position both have an effect.

A high centre of gravity leads to instability. The centre of gravity is lowered both by increasing the mass of the board and by reducing the thickness of the board where the rider stands.

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[LBCrew]

So "flexible torsion box" does not refer to torsion flex. A little confusing, but ok...

I think flexing robs speed by wasting energy. Boards need to flex for other reasons, but gaining speed is not one of them.

Added weight makes sense to me for some of your design goals... greater momentum to drive through sections being a big one. But what you state as a "simple matter of physics" is, in my opinion, based on my design theories, is an oversimplification. I do not overemphasize gravitational potential energy in design theory based on the idea that the wave itself... the movement of water... determines to a large degree what design features will work best. And here I am referring to boards of light weight and relatively small size when compared to yours. Concaves, fins, rail edges, template... all come together for the purpose of managing wave energy and the movement of water up the face of the wave and toward the beach. Gravity is a constant force, and easily dealt with from a design perspective. All the other factors that relate to energy input into the board/wave/rider "system" (for lack of a better term) mean much more to me than you... or so it seems to me at this point in our conversation. And I agree that rider input, aside from weighting and unweighting, is a relatively small component in the equation.

Where does "lift," in the vernacular of surfboard design, come into play in your designs?

[brewengineer]

So "flexible torsion box" does not refer to torsion flex. A little confusing, but ok...

I think flexing robs speed by wasting energy. Boards need to flex for other reasons, but gaining speed is not one of them.

Added weight makes sense to me for some of your design goals... greater momentum to drive through sections being a big one. But what you state as a "simple matter of physics" is, in my opinion, based on my design theories, is an oversimplification. I do not overemphasize gravitational potential energy in design theory based on the idea that the wave itself... the movement of water... determines to a large degree what design features will work best. And here I am referring to boards of light weight and relatively small size when compared to yours. Concaves, fins, rail edges, template... all come together for the purpose of managing wave energy and the movement of water up the face of the wave and toward the beach. Gravity is a constant force, and easily dealt with from a design perspective. All the other factors that relate to energy input into the board/wave/rider "system" (for lack of a better term) mean much more to me than you... or so it seems to me at this point in our conversation. And I agree that rider input, aside from weighting and unweighting, is a relatively small component in the equation.

Where does "lift," in the vernacular of surfboard design, come into play in your designs?

http://www.exo.net/~pauld/activities...ofsurfing.html

Roy gives gravity too much credit. Hydrodynamic forces are just as important.

[Roy Stuart]

I think flexing robs speed by wasting energy. Boards need to flex for other reasons, but gaining speed is not one of them.

It needs to br done correctly, the main mistake I see is making shortboards flex when it is really the province of long boards which are ridden from a central position. The load positions and fulcrum don't allow it to be effective for shortboards and mals and flex can indeed slow them down.

Added weight makes sense to me for some of your design goals... greater momentum to drive through sections being a big one. But what you state as a "simple matter of physics" is, in my opinion, based on my design theories, is an oversimplification. I do not overemphasize gravitational potential energy in design theory based on the idea that the wave itself... the movement of water... determines to a large degree what design features will work best. And here I am referring to boards of light weight and relatively small size when compared to yours. Concaves, fins, rail edges, template... all come together for the purpose of managing wave energy and the movement of water up the face of the wave and toward the beach. Gravity is a constant force, and easily dealt with from a design perspective. All the other factors that relate to energy input into the board/wave/rider "system" (for lack of a better term) mean much more to me than you... or so it seems to me at this point in our conversation. And I agree that rider input, aside from weighting and unweighting, is a relatively small component in the equation.

Of course surfboard shape and hydrodynamic forces are vitally important, I was merely making the simple but often misunderstood point that the wave imparts energy to board and rider by lifting them, this lifting action imparts gravitational potential energy to the board and rider in proportion to their mass.... the wave does more work when lifting heavier objects. Since the vast majority of the energy which drives board and rider is applied through gravity, there is no acceleration disadvantage for a heavier board and rider.

It's not a matter of gravity OR hydrodynamic forces.

Where does "lift," in the vernacular of surfboard design, come into play in your designs?

That's a huge topic, where would you like to start?

Surfboards use buoyant ( displacement based ) and planing ( dynamic) lift. We go to great lengths to tailor the distribution of both kinds of lift as required. High dynamic lift areas act as fulcrums, this needs to be understood when designing for flex, I haven't seen anyone else ever use this approach, but it is vital.


http://www.roystuart.biz/2009/10/buo...ning-lift.html

http://www.roystuart.biz/2013/01/the...-on-video.html

http://www.roystuart.biz/2010/12/sur...-pressure.html

http://www.roystuart.biz/2010/12/sur...essure_04.html

[Roy Stuart]

http://www.exo.net/~pauld/activities...ofsurfing.html

Roy gives gravity too much credit. Hydrodynamic forces are just as important.

That's a ridiculous comment, and much of the information on the site is below par, for example this old chestnut of a myth:

"You savor the rush of acceleration as tons of moving water push you faster and faster. "

In reality the wave lifts the surfboard and rider, hydrodynamic forces are required for this to happen ( otherwise the board and rider would not lift, the wave would simply move over them) ... this lifting action imparts gravitational potential energy to board and rider, and it is this energy which moves the board as it is transferred into kinetic energy.

When up and riding, the wave can directly push board and rider horizontally only when the rider is on the throwing lip, or when being pushed by whitewater.



.

[brewengineer]

That's a ridiculous comment, and much of the information on the site is below par, for example this old chestnut of a myth:

"You savor the rush of acceleration as tons of moving water push you faster and faster. "

In reality the wave lifts the surfboard and rider, hydrodynamic forces are required for this to happen ( otherwise the board and rider would not lift, the wave would simply move over them) ... this lifting action imparts gravitational potential energy to board and rider, and it is this energy which moves the board as it is transferred into kinetic energy.

When up and riding, the wave can directly push board and rider horizontally only when the rider is on the throwing lip, or when being pushed by whitewater.



.

No, actually you have no concept of physics. There are multiple forces from the wave, and the speed of the wave is important for surfing speed.

http://www.rodndtube.com/surf/info/i...10N3-69-07.pdf

But I am sure you know more than someone with a PhD in physics.

[Koki Barrels]

In the videos you have posted of you surfing, I can see that you do gain a decent amount of speed and the added weight of the board actually looks like it helps to keep that momentum. Have you ever considered linking up with a surf shop on the east coast and maybe having a board there that people could demo, maybe pay like the cost of a board rental for a day, so that some of us could try it out...'cause i highly doubt any of us can afford one.

Here is the website for one of the local shops around here, they would probably be more than happy to store and demo your board...http://www.chaunceyssurfshop.com/Tweets.htm

[LBCrew]

...the wave lifts the surfboard and rider, hydrodynamic forces are required for this to happen ( otherwise the board and rider would not lift, the wave would simply move over them) ... this lifting action imparts gravitational potential energy to board and rider, and it is this energy which moves the board as it is transferred into kinetic energy.

I would say, again, that this is an oversimplification. I believe it is correct in the sense that gravity pulls the board and rider down... wave energy pushes the rider up... and the horizontal motion of the board/rider is, in part, is a play between the two. This seems to be particularly true for your boards, which are clearly lifted at certain planing angles, and dropped at others. But I would argue that typical shortboards, with modern fin configurations and bottom contours, are ridden very differently, relying much less on "climb and drop" forces.

When up and riding, the wave can directly push board and rider horizontally only when the rider is on the throwing lip, or when being pushed by whitewater.

I disagree with this last statement completely. Typical modern surfboards move fastest on the face of the wave where the water is moving the fastest... and they do so because they are able to tap into that kinetic energy with design features I do not believe are present in your boards... nor should they.

Roy... I'm convinced now more than ever, based on just your past few posts... that your boards work exactly the way you want them to, at least for now. I think I understand at least some of the principles upon which your designs are focused, and I think you have a solid understanding about how/why they work the way they do. And anyone who wishes to surf the way you do... the way your designs are intended to be ridden... would find your boards a lot of fun. Personally, I'm not interested. My surfing goals... what [I]feels good[I] to me when I'm up and riding... are very different from what I see in your videos.

Whether your style of surfing... and the performance of your boards... is popular or not matters little to me. What the value of your boards are and who buys them matter even less. (People have spent obscene amounts of money on stranger things than what you have to offer the marketplace.)