A headwind, alone, is what makes a sailboat move upwind. Therefore it is not analogous to surfing and they should abandon trying to think of surfing in the same way.
Slim,
it’s comments like this that lead me to believe that you don’t understand the concept of ‘lift’, whether it be aerodynamic or hydrodynamic.
I cannot see how any analysis of surfing can exclude the force of hydrodynamic lift. And I feel that the only reason your description of surfing excludes hydrodynamic lift is that you simply don’t understand it.
Even if you don’t get the physics, perhaps just looking at boards would show you that they are designed to provide lift and ‘hold’ (among other things). Rail shapes and outlines (and fins) effect ‘hold’ in the wave. But why would we need ‘hold’ if gravity is just accelerating us down a slope? Are we just on the wave or are we slightly in it?
Disclaimer: please don’t take this personally, I’m not trying to annoy anyone here. And this should go for all my posts. I’m not interested in personal slagging off of people and their views.
My shortr comment on gravity was only to point out the difference of the physics involved throughout the ride within the crest. Gravity is not involved in the underwater-ride because it doesn´t generate a force on a rider, who´s specific weight ( shortly: weight compared to equal volume of water) is “1”, meaning “no sinking or rising within water”.
That is,as Janklow pointed out, completely different from the ride on the water-surface.
So it must be clear by itself, that the dolphins do not need to generate lift for their ride in any way. But they surely need to overcome drag, as you`ve put it, for which they make use of different waterspeed-layers and -directions within the moving crest.
A headwind, alone, is what makes a sailboat move upwind. Therefore it is not analogous to surfing and they should abandon trying to think of surfing in the same way.
Slim,
it’s comments like this that lead me to believe that you don’t understand the concept of ‘lift’, whether it be aerodynamic or hydrodynamic.
I understand it fine. If you are going to tell me that it is hydrodynamic lift and not the wind is the force that moves the sailboat, then I’ll understand why you think it’s lift and not gravity that moves the surfboard. But I’ll still think it’s a silly way to look at things. Next you’ll be telling me that it is friction that is the main force behind me walking. Just because something is present (lift, friction, etc.), even necessarily so, it does not mean it is the force behind an action.
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Even if you don't get the physics, perhaps just looking at boards would show you that they are designed to provide lift and 'hold' (among other things). Rail shapes and outlines (and fins) effect 'hold' in the wave. But why would we need 'hold' if gravity is just accelerating us down a slope? Are we just on the wave or are we slightly in it?
We need hold so that we can position ourselves at various angles to the wave. We are at times on the wave and at times in the wave. I don’t think this paragraph is relevant to the discussion about gravity.
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Disclaimer: please don't take this personally, I'm not trying to annoy anyone here. And this should go for all my posts. I'm not interested in personal slagging off of people and their views.
Please knock off all the “i have plenty of black friends,” type disclaimers. If you really don’t want to do those things, just don’t do them. It’s crazy to do them and then explain it away by disclaimers or preface them with “don’t take this the wrong way, but…” type comments. All you have to do is stick to writing about the topic, and not the people in this thread. What’s so hard about that? Just eliminate all the comments that refer to another person in a judgmental way, and just post a counter-argument to the things posited by the other writers. (you have four “you” in the last post that are comments about me: instead, just argue for your position and against mine)
somebody needs to draw a force vector diagram illustrating that when we add the forces of lift and gravity we get a resultant force driving us down line.
People seem to be stuck in the argument of which is the ‘main’ force. And i think one is nothing without the other.
When we consider the ‘main’ force perhaps this is relative to ones perspective. I.e. if you’re a shaper you’re probably heavily into designing a board with respect to the lift it generates.
How do we decide which is the ‘main’ force - not that i care about ranking forces.
Does one force appear to be the ‘main’ force because it has the great magnitude or the greatest component in the direction of travel?
again a force vector diagram may illustrate this point.
Perhaps it is better to state that lift and gravity provide the main ‘propulsive’ forces in surfing, while drag slows us down.
I am in agreement with your post #265, above. My focus was/is to identify the ‘‘main’’ force. But even that is a moving target. A rider surely taps gravity when dropping into a bottom turn, but quickly abandons it for the rest of the ride. A vector diagram of all the forces would be instructive. And for me, magnitude would identify the ‘‘main’’ force being utilized by the rider on a wave.
A rider surely taps gravity when dropping into a bottom turn, but quickly abandons it for the rest of the ride.
This is the crux of this argument. I can’t believe it myself, but there it is.
As far as lift goes, of course lift is operative on a planing craft, but the deflection of flows is what constitutes lift. The water you encounter on the way around the slope of a wave is subject to your already-planing craft’s surfaces, and those surfaces deflect the water in their way, and that is lift.
But to clear up at least these central pieces of the opposing argument(s):
The argument is made that gravity’s influence on a surfer disappears at some point.
The argument is made that there is what amounts to a current rushing up the face of the wave.
The argument is made that a fin or fins “tap into” this current and actually “propels” the board, rather than providing a plane of lifting resistance to the water that is in the way as the rider makes his way across with the aid of gravity and inertia he engenders while dropping, trimming, and turning.
The argument is made that the surfboard bottom is using this current rushing up the face of the wave to “propel” itself in the other direction, at all times, and gravity’s influence is nil, or at least minimal, no matter the outward appearance of gravitationally-induced acceleration.
The argument is made that gravity’s influence on a surfer disappears at some point.
The argument is made that there is what amounts to a current rushing up the face of the wave.
The argument is made that a fin or fins “tap into” this current and actually “propels” the board, rather than providing a plane of lifting resistance to the water that is in the way as the rider makes his way across with the aid of gravity and inertia he engenders while dropping, trimming, and turning.
The argument is made that the surfboard bottom is using this current rushing up the face of the wave to “propel” itself in the other direction, at all times, and gravity’s influence is nil, or at least minimal, no matter the outward appearance of gravitationally-induced acceleration.
These are not very fair representations of what has been argued.
How many times do I have to say that water flow doesn’t imply current, or stream?
Maybe they’re not representative of what you have argued, but they are fair enough statements of what others have argued.
As for your terminology, if you’re talking about water gaining vertically without a current or flow up the face, you’re talking about a slope progressing toward shore as the wave pulse propagates, and the flow the board sees is all relative to the board’s progress, which is owing to gravity and the slope of the face and momentum and centrifugal force engendered by the rider.
edit: The difference between the current lifting your board up and the slope simply rising might best be illustrated thus, with a static moment in time assumed:
if you somehow support a plank with a vertical stream of water out of a hose, and you incline the plank, …?
If you pick it up with your hand, and incline it such that it starts sliding off your hand…?
What is the force that causes the effect in both cases?
Hi Janklow - I don’t know about anyone else, but I can suppose, so would you mind filling in some of your profile? For one with strong opinions, like many here, it may be nice for some of us to have a better picture of who Janklow is.
I think everyone here agrees gravity is a big deal. I was taken aback by the “radical flow” theory/ist, but I was reminded of the importance of the relative movement of water up the face, and the effect it can have on the board and riders movement. I think the link to the guys paper will spell it out. The point is, as one mentioned about planes/gliders, the “flow” on the fins can impart speed to the board-rider - aside from gravity.
Without putting too fine a point on it, credentials as far as the thread here would be or could very well be worth a hill of beans–I could be an engineer, or a travel agent, or a ditchdigger, or a loan broker, and you may take or leave the ideas I enunciate or talk about here, such as the universal effects of gravity, as you like.
As far as that goes, I don’t care who ya are or what you say you are or who you know, or where you’ve been, this subject gets downright humorous when people talk about gravity going away, or put its importance in any kind of diminutive terms!
The slope of the wave is a curve right? Goes to vertical and over vertical at the top? So what you have is that kind of a slope or wall, as it may be, moving through space. If you’re on the wave, you’re subject to that wall or slope coming at you if you turn toward it, or moving under you from behind. The slide or launch those things induce are predictable.
The water is a hill. Your board is planing. The flows are relative to your board’s planing speed. Your board’s planing speed is given by its gravitational acceleration. When you turn toward the crest or face, you find your planing speed combining with the wave’s speed toward you.
In all these pages, nobody has been able to outline anything on that side in any kind of terms that make sense. You can say this or that about flows, but I don’t think you will be able to really explain how it’s working in terms that refute our argument in any way, because your terms are merging into our argument, and the other guys can’t make their explanation work, because their current or whatever they term it is going the wrong way to be “propelling” the act of surfing.
The slope is moving toward you at times, and if you’re turning toward the crest and it’s coming at you at the same time, like when Bill found himself making a quick trip into the atmosphere, the closing rate can be quite something and induce air, no argument.
You present your board bottom and fins to water as you slide, but what’s making you slide is gravity. The elementary argument is that when you surf, you’re sliding down a slope and using that gravity-induced momentum and the wave’s speed and your bottom and fins to do the whole shot.
I agree with you (I think). But I also agree with Bill (I think).
Gravity is pulling you down. The wave is moving forward. But I also think that the water is moving up (and forward, and back, in different spots, but mostly up).
Lift is created by the fins and the board because gravity is pulling you down. But the water is moving in the opposite (or near the opposite direction) direction of gravity, and it is enhancing the lift.
I also think that the moving water changes the AoA of the surfboard and the fins. As AoA is with regard to how the fluid is moving past the object, regardless if it is the fluid that is moving, or the object, or both. When you take the vector of the surfboard movement and sum the vector of the water movement you get the actual vector of movement (relative to the board).
This is why surfing is different than skateboarding, snowboarding, and why people incorporate the analogies of airplanes and sailboats to help explain what is happening.
Hey Janklow - Just a social courtesy thing. Seems to me you might think about playing nice. And to be sure, your opinion with standing, many here may give more credit to what people say, when they know the person has been involved in the surf industry for decades/over half a century, has/is working at doctorate level science in the field, etc…
No one is discounting gravity. It has been pointed out, all the science has been posted here plenty of times, and it is complicated and hard to understand. I’ve backed away from the math, as it was hard, and didn’t help my understanding.