Yeh, I forgot one force. The surfer. Probably the most important one.
TaylorO - you’re on the right track but in water wave theory gravity is termed the restoring force
see http://en.wikipedia.org/wiki/Ocean_surface_wave#Types_of_wind_waves
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I am still looking for proof of the moving water theory.
do you mean you don’t believe that water is moving up the face of the wave?
DrAL - Sorry for the forgotten understanding of the “restoring force.” I knew it had something to do with it.
What I’m still unconvinced about is the level of importance of water moving up the face. At this point I’d settle for some thing to convince me it makes a big difference. I’m settling for: there are forces at work on the surfboard; be they from gravity, water flow, combination of both, or as Bill T. pointed out, much to my amusement, “magic.”
The more I think about it, the more I think friction is a much bigger factor than water moving up the face. I’ll pass on the science and say, I’ve seen others have to many waves pass under them/get hung up in the lip/at the top when, as far as I can tell what some here are suggesting, the water flow should have helped them attain planning speed, and they should have caught the wave.
Still looking for knowledge…
TaylorO,
How does the water get to the top of the face if it doesn’t move there?
Is there something incorrect about his sequence?
Sorry I wasn’t clear, I’ve changed my position on water moving, but remain unconvinced it is a major factor, if one is to pull it out as a factor.
As, I’ve written around this issue, and, to borrow from LeeV - even while perverting his intent… Ha! No offense Lee. It’s all relative. And, as others have pointed out, there is so much going on in the overall function of riding a board on a wave, I’m not sure it is a critical point.
To continue to argue for the sake of such: The picture below is only a 2-D side view as the wave crests, prior to moving to cresting the points only move up in space, and in most cases the velocity of that movement - again, my position on this - is not enough to induce planing speed.
Never the less ob - thanks for the good questions - good to see someone on a quest for knowledge.
Really? What is planing? What is planing speed? What factors determine whether or not a craft will plan? You seem fairly sure in your comments, my guess is that your insight would clear up a lot.
If you have access to a drawing program (e.g. MS Paint), any diagrams that would make your answers clearer would be appreciated.
kc
I’ll take that as a complement KC, but my comp skills are long gone. I still have some half finished “paintings” I started, but didn’t even finish for lack of time, and then to post… Ahhhh! I once had a bunch of pics from a project, that I couldn’t get on my comp, let alone post…
I have my opinions, some based on “fact,” some based on empirical observation, and some in contradiction to what other more learned, experienced folk here would posit.
At this point, on this subject, I will accent to water moving up the face of a wave, more so on certain types - as Teahpoo (sp?), and Pipe were brought up - but as for the speed of the board relative to the water surface to attain planing speed; a combination of paddle speed and the speed of the water moving up the face. It seems to me friction in/on the water surface creates more interference than speed. As I said, I base this on observation because; it seems to me I, and others, would catch more waves, rather than have the wave jack up under them and pass them by. Simple as that, and that is just about catching the wave - Because some one pointed it out to me, but I’m still not “feeling” it. I’m not even beginning to think about “water flowing” once planning speed is obtained, and one starts riding. I think the basic definition of planning is when the speed of the craft is greater than the force of gravity and fiction to hold it down in the water. Like the classic water ski start… riding on, not in the water… and of course this doesn’t deal with the fins and rail action… Science or not, there are some forces at work, and to me it’s all about pressure differences, and balancing speed and control. I guess I may sound sure in my comments, only in that, I don’t feel anyone has been able to convince me otherwise, and I try to be open minded, and I don’t think I’m an idiot, but who knows. I’m still waiting for an “ah ah” moment.
TaylorO,
If water was moving down the face of the wave would we catch more waves?
The problem with catching a wave is not only do we have to paddle to catch the wave as it moves relative to the earth, but because water is sucking up the face we also have to paddle faster again, because we’re getting sucked backwards. Drag is the problem here. longboards paddle faster - less drag, on it earlier… catching more waves
Once we’re on the wave the fact that the water is moving up the face of the wave means we plane easier or sooner than if it wasn’t moving (higher relative velocity). Think of a waterskier being pulled up a river just at the speed he needs to start planing (lift out of the water, so he’s skipping along the surface), and then think of him being pulled down the river. How would this look to an observer on the bank? i.e. what ‘relative’ speeds would he have to travel in each direction to maintain planing?
planing speed aside, the fact that water is moving up the wave has another effect, one that Bill alluded to earlier. That is, what happens when you’re fin(s) and rails are in the wave (when your trimming along diagonally down the line)?
Which is the high pressure side of the fin? We know that drag will always oppose the direction of motion but which way is the lift force from the fin acting?
here’s a bad example of flowrider in action
http://www.youtube.com/watch?v=IRwLQc8sisY&feature=related
obviously not quite the same as a real wave but worth thinking about, especially regarding equilibrium of forces.
just the same as my quarter pipe with the conveyor belt idea
(as a side note i think the water in flowrider moves very fast to allow smaller boards to provide the necessary lift, if the wave shape, and health and safety, would allow them to use 9’ board i’m sure they’d shut the valve a little)
goodnight folks
just to clarify something
I reckon you would have to be an amazing paddler to reach a speed where you start planing.
you’re on a displacement craft until you’re charging down the wave,
(much like the waterskier at the start of his tow, then he reaches a speed where he lifts up on top of the water surface, now he’s planing, less drag, more speed, etc.)
Here is a simplistic diagram of what I think the forces are. I’m pretty sure its wrong but it may serve as a point for discussion.
In the diagram the frame of reference is the wave not the movement over ground, inertia has been overcome and we are accelerating from paddling at this point.
You need to overcome water molecule movement, drag and possibly offshore wind with paddling effort and the use of gravity (dropping your head). Bouyancy is shown as a neutral force in relation to forward movement. However changing the impact of buoyancy with board design or body placement can help or hinder depending on how you use it. You also have drag and friction to overcome which are board parameter considerations, rocker, rails and bottom contours.
now we’re talkin’. once you let go of the fact that the wave is moving towards the beach and draw it as you have i think things get simpler and easier to understand, while still remaining valid.
the ‘water molecule movement’ is not necessarily a force but does add to the drag force (relative velocity between the water particles to the board).
so the forces at this point are:
gravitational force on the mass of the board and surfer - always vertically down
bouyancy force - out of the wave
paddling force - in direction of motion
drag (and i’ll put wind drag under here too) - against direction of motion
If you overcome the drag you will start moving down the face (accelerated by gravity), if you don’t you get pulled over the crest by drag.
Let’s say you win, now stand up and draw me a picture!!!
please
Just an observation: Without the ‘‘circular’’ movement of water molecules, there is NO WAVE. So, it seems to me that it is a very iimportant force. Dirty little secret is, that it is a major contributor to driving the board and rider across the wave. Tapping that energy is also what produces ‘‘airs’’ , intentional, and unintentional.
Bill, I didn’t draw the full elliptical orbit in the diagram, I assume it’s well known, I only included the intersect with the surfboard on the face. yes tapping into that force is magic. I only wish I could do it more efficiently. I guess thats why I love Fish and Bonzers so much, you can really feel the wave.
Bill please explain your comments about the circular motion of the water particles, I think you’re only adding to the confusion.
My view it that if we look side on at a wave as it passes us and dye one water particle, it would trace a circular orbit. Ending where it started.
Now if we follow the wave, the wave is our reference like in Burnsie’s drawing, still looking side on, when we dye the particle, let’s say on the surface, where will it go?
It will have max horizontal velocity toward the wave in the trough, max upward vertical velocity somewhere around the face, and then at the crest it will appear to slow, then go over the crest speeding up again, downwards and horizontally.
So if we’re going with the wave, passing over lots of particles as they fly under us providing us with lift, who cares what path they make? we only care which way they are going when we meet them. And I believe that this is generally up the wave (where we surf), but at different speeds depending on where you are, like right p by the lip or out in the flats.
And yes you can make use of this to get air and smack the lip, and drive across the wave…
But how Bill? Tell us about fins and rails!!!
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it is a major contributor to driving the board and rider across the wave.
Well, this is the crux of the argument (hypothesis). The corollary premise is that without it, surfing would not work down the line. But the models of snowboarding and skateboarding diagonally down a hill I think prove otherwise. So what’s lacking is a proof or argument of why and how surfing is fundamentally physically different. Cuz to me, it’s just renewing grade and you deflect against the pull of gravity and you accelerate into the pull of gravity and you can feel those and you can see the acceleration part for your self in any surfing video you care to watch anywhere.
Definitively speaking, all the assertions including mine are just opinions, but video shows gravitational acceleration. It also bears mentioning that the wave crest is moving forward so what are basically braking turns away from gravity toward the crest are aided by that. You turn toward the crest and what was a deceleration becomes an acceleration, given the crest moving toward you at 12-15 mph.
I could easily put together a model of trim with a skateboard weighted on one side, a roller, and a rug, to prove the “boardsports are driven by lateral deflection against gravity” part of my argument. I don’t have to, because it is self-evident. I haven’t heard anything but received wisdom and assertions from the “critical flow” side. And it bears mentioning that intuitions and physical perceptions about physical phenomena are constantly proven wrong. Ask any instrument-rated pilot. Ask JFK Jr.
.02
Im not sure what Bill is hinting at but as a possibly related observation, your diagram is lacking a pressure force under the board. Flat objects planing over water have pressure exerted underneath. Fins create additional pressure board lift as well.
KCasey put together an excellent free body diagram on Sways a few weeks back. But it was riddled with geometric jargon that tended to loose the limited audience. Only MTB was able to participate. I had that ability for a long while but I lost interest in that sort of micro-analytics. Not very usefull in everyday life. Altho I can still read them.
Onward…
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Well, this is the crux of the argument (hypothesis). The corollary premise is that without it, surfing would not work down the line. But the models of snowboarding and skateboarding diagonally down a hill I think prove otherwise. So what’s lacking is a proof or argument of why and how surfing is fundamentally physically different. Cuz to me, it’s just renewing grade and you deflect against the pull of gravity and you accelerate into the pull of gravity and you can feel those and you can see the acceleration part for your self in any surfing video you care to watch anywhere.
But you can’t do a bottom turn on a quarter pipe with a skateboard or snowboard like you can with a surfboard on a wave. Part of the difference is the fact that the wave is moving toward the surfer in the trough of the wave. The other part is that the water is moving back toward the wave, pushing the surfer whose fins and rail are being pushed back by the wave, at the trough.
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But you can’t do a bottom turn on a quarter pipe with a skateboard or snowboard like you can with a surfboard on a wave. Part of the difference is the fact that the wave is moving toward the surfer in the trough of the wave. The other part is that the water is moving back toward the wave, pushing the surfer whose fins and rail are being pushed back by the wave, at the trough.
Exactly the frame of reference, thats why the diagram only considered the wave as stationary to get a handle the possible forces. Now in the real world look at this sequence of NPJ and see and see how fast his wake moves up the wave.
Looks fine. I would exercise some parsimony and forget about the wind and buoyancy forces. Wind really isn’t apart of surfing proper -i.e. it’s ancillary, and the role of hydrostatic lift in surfing is minimal at best, unless ‘paddling’ is now ‘surfing’, which it isn’t. But each to his own.
A little more (somewhat off topic) nonsense…
Breaking waves are decelerating, that’s why they shear. The term ‘throw a lip’ is incorrect though seemingly appropriate when if you duck dive a little to late. The lower portions of the wave are decelerating faster than the upper portions – hence the shear.
Even better?
If the wave is shearing at the top, its shearing in the middle too, but to a lesser extent… actually make that right down to the bottom too –i.e. that’s why the face forms.
…huh?
If the wave is shearing that would suggest that if the wetted area of a surfboard vertically spans a bit of the wave face, it would experience a differential flow pattern over that vertical profile.
…huh, huh?
Actually it’s also true for the horizontal, as the curl is moving slower than the shoulder.
… huh, huh, huh?
Just thought I’d mention this because it has implications with respect to planing as applied to surfing, and hence design.
(By the way, my rants about dynamics can be found by doing a search on moi, right back into the Neanderthal days prior to Swaylock updating his software - in a nutshell, surfing is about planing. Or using your diagram, if you take away wind and bouyancy, which I assume means hydrostatic lift, you’ve got those nasty little bits of water hitting the bottom of the board exchanging/transfering momentum, a.k.a planing.)
kc
ob - Sorry if I come across the kook I can, and may, be, but I’d argue the board and rider are much more akin to “flying” through and over the water, than being pushed back into/up the wave by the water, and as the pictures in the next post shows, to me, the water isn’t moving that fast compared to the rider, and, again, it may just be my bias, but I don’t think I’m holding on to a bias, as I don’t care how it’s described - just how it works, but I would argue the wave seems to move into the wake far more than the wake moves up/into the wave. If you watch surfing from a pier, jetty, or cliff - from right above, it’s always looked to me like the wave moves into what ever is in front of it.
God - it’s like a bad addiction, I say I won’t post, but then… ahhhh Ha!