That is an interesting simultion.
I’d be curious if you feel this supports you’re prior point, or how it might help me understand it?
Kevin
I dunno how far you could take all that. I’m pretty certain that there are fast-diminishing returns, losses to maneuverability coming first
My prior point, and pretty much all the way along has been, and still is, what is the flow’s (surface shear) velocity up the face, in terms of what is not accounted for by the total waveform’s velocity?
And how do you theorize that we as surfers exploit this all the time?
Because in repeating the circular diagram and/or its implications several times now, you’ve confused the issue, or rather are you saying we are actually taking more advantage of a flow that goes up the face (then [I take it you assert] reverses direction near the top) than combined gravity and waveform V?
Kotzebue’s got it covered–read those posts again.
I’ve looked around quite a bit now and the info I see says the hydraulic flow toward the wave out ahead of a wave is never even all that close to overall forward waveform V and nets out less than zero, actually, overcome by the forward wave velocity once you’re on the face. The diagram above has the overall waveform V at 1.5 M and you see that the surface shear is less than that at every stage/gradient
Actually the more I look at the illustration the more encouraged I get.
It’s nice to know that you’re looking at the velocity of water particles. It’s a first step towards seeing the wave as mass transport –i.e. flow.
Regardless of predominant component of the flow (upwards or towards the beach), it’s the presentation of the bottom of the board with respect to the flow that will determine how the board will interact with the flow. So if the flow is almost straight forward, roll the board towards the beach a little, and maybe increase your pitch a bit, that’s if you wanted to go down-the-line. If you want to just get out in front, that is go straight; you might just increase your pitch a smig. If the wave is powerful enough, it doesn’t take much of a change in the boards bottom orientation to make a big difference. (Which is unlikely to be the case for the wave depicted in the illustration.)
I’ve read the gravity arguments, and I’ve expressed my disagreement. This does not mean I do not believe gravity does not play important role. Its just that I do not believe that surfing is skiing, sleighing or a what is usually meant by the term ‘gravity sport’.
I’ve re-read Kotzebue’s posts. I see no reason to change my replies.
Very nice illustration, thanks.
Kevin
I did get the best unintentional joke and a succinct expression of your whole argument in one shot out of your last post:
“I’ve read the gravity arguments and I’ve expressed my disagreement.”
I laughed out loud there, I’ll tell you-- actually that line is a great one to read and re-read…I may make that one my signature–holy shit…
you have no measured flow velocity relative to the waveform’s overall velocity, do you…
I questioned your unsubstantiated assertions in a forthright fashion and you evaded the challenges. If you show up to the chess club here in Texas and start talking about some quantum energy field that’s actually moving the pieces around, you’d better have some evidence, or someone is gonna tell you that your assertions are unsubstantiated in a much more forthright fashion that I have heretofore.
CHALLENGE:
Present measured evidence that this flow, in whichever direction, or as you assert, to and fro, to and fro, exceeds the beachward velocity of the crest in whatever direction you like, and then explain how we exploit that. 3 OR 4 BULLET POINTS OUGHT TO DO IT. NO KEVIN-GENERATED DIAGRAMS SHOULD BE NECESSARY.
Otherwise, as the US Navy’s graphic shows, the crest’s velocity together with the grade it generates on on the face combined are the whole story of what generates our momentum in surfing. You have lost. You can’t fight the US Navy on waves, man.
Have you Googled this shit? Or did you just start holding forth…or are you some kind of rightwing agent sent to mindfuck the clever people at this website?
Try it. Do a little research on MEASURED surface shear flow speeds, and present your evidence. (Don’t be too disappointed.)
“I’ve read the gravity arguments and I’ve expressed my disagreement.” KCasey
So I’m sitting there eating my chicken sandwich and then I realized the joke was on me.
All waves decelerated as they shoal, in your example, a fairly small wave is allow to shoal to the point where it has literally stopped, and when it does, because the top portions have failed to keep up with the deceleration, they shear off, or continue to move forward. What makes this illustration unique is that the wave has literally slowed to where it has stopped.
As I continued to eat, I thought, so this guy is under the impression that a wave must stop before it breaks? That’s when I got the joke.
Then again maybe you do believe the bottom portion of a wave must come to a halt in order for a wave to break. I’m not sure it would explain what you’ve written so far, but it would explain a lot.
Anyway, nice.
As for your challenge, if you don’t buy into what I have said so far, fine. There is nothing to win here, at least as far as I’m concerned. And I don’t see whats at stake - its an interpretation, you agree or you don’t. Noting you’ve written has made me question what I have written. And the same seems to be true for you. So, if what I’ve said makes no sense to you, great, go with what does.
Kevin
Sounds like you’re dancing, professor. I don’t savvy. Put up or employ the standard alternative.
Nice breaking wave diagrams thanks.
.
so we are all agreed its not a gravity sport!
but relative to flow and forward velocity of a breaking wave.
id like to put some practical experience to Kevins theory
im sure some of you are more than familiar with what its like to go straight forward on a broken wave.
and possibly the feeling of being tumbled by a wall of white water and dragged over a sharp reef.
i imagine you would have enough practical exerience the sensation of a bottom turn in the pocket of a breaking wave.
here are some bullets.
-
speed can be pumped from a bottom turn at the bottom of an open wave face(ie you can come out of a turn faster then when you enter)
-
speed can be pumped from behind the whitewater travelling sideways across the front of whitewater
-
No(or very little) extra speed can be pumped from going straight in
-
More speed can be pumped in a bottom turn on an open face then in front of white water(actually its the point just in front of the white water where you can harness the most energy form a wave)
5.A broken wave(although loosing much of its energy)Still maintains plenty of forward velocity.(enough to hold you done for 10 seconds and drag you over the reef)
6.If the waves maintains velocity after it broken yet less speed is generated from pumping behind the whitewater.there must be other forces in the trim equation, than gravity and forward velocity
7.If speed cant be generated by pumping going straight, as some do, there must be other forces than forward velocity involved in the trim equation.
-
for me to derive more pleasure and speed from surfing .I prefer to harness speed in turns on an unbroken face of a wave
-
if you can generate more speed in a bottom turn on the unbroken face than you can in front of whitewater.then upward flow of water must be a contributing factor to generating speed from a wave on a surfboard
if you get the hang of going sideways on a wave,things might become clearer 
Nope.
( :
Let’ s all just contact our friendly neighborhood PhD active in the actual quantification of the various values inherent in real ocean wave dynamics, shall we? Ask your guy what is the velocity of the surface layer ahead of and on the face of surf zone waves.
This surface shear flow velocity thing should be common knowledge for those guys–we’ll have all this sorted in no time.
Simple enough.
I’ll own up if I’m wrong.
Love,
j
how do they measure it
do they get wet
and can they surf?
im assuming the surface layer sheer, blends to the centre of the wave
stronger velocity at the surface and getting less and less toward the cenre
See, Paul, that’s it, just between you and me, this is all bullshit without this one critical piece of data. If this KCasey fellow wanted to, he could have hit me between the eyes with this one critical bit (or set) of information a long time ago, cuddenee.
It ain’t like it’s hard to measure that.
My e-mail’s sent. I’ll get some more out tomorrow.
Drinking one for ye
j
Here’s an excellent particle velocity page:
http://www.coastal.udel.edu/faculty/rad/linearplot.html
Run a bunch of scenarios to get a feel for the particle velocities involved (the applet gives maximums of horizontal and vertical components). Please note, that as the wave shoals (moves into shallower water) the maximums do not necessarily occur simultaneously (see below.)
I would suggest running a series, progressively moving the wave into shallower water. The applet will actually tell you when it thinks the wave has broken.
(I have not communicated with the author, but it appears to be a classical treatment. Please contact the author and drill him about the results.)
To get a feel for the pressures which impacting flows can generate (that have a given particle velocity associated with them), use the quick and dirty dimensional treatment,
p = d*|v|*|v|,
where,
p is pressure in Pa (= N/squared-meter)
d is density in kg/cubic-meter (I’d go with 1000 kg/cubic-meters for water.)
v is magnitude of velocity
or in words,
pressure equals the density of the liquid times the magnitude of the velocity squared.
If the wave form you use to get v from is very distorted (breaking or pretty near breaking) you will not be able to calculate the magnitude of v using the maximums provided. The reason being is that, as the wave shoals these maximums occur at different points in the cycle. So just use the bigger of the two numbers provided, which should put you in the ballpark (roughly.)
But how much force is produced? You’ll need a surface area for that, say A square-meters, (try to estimate the amount of surface area that’s usually wet on your board, crude approximation will likely be good enough.)
p*A = F
Have fun.
By the way, I do not wish to imply that the numbers you’ll generate are some how the ‘final’ numbers. Hopefully what the above exercise will provide is a feel for the forces involved.
Kevin
Quote:
so we are all agreed its not a gravity sport!
I don’t know how you figured that one out. . . surfing is most definitely a gravity sport. . . . but go ahead and manufacture a more mysterious myth if you want to. . … bottom line is that most of the propulsion in surfing is applied by gravity. . . . therefore it is a gravity sport. . . . . . . . 
Quote:
if you get the hang of going sideways on a wave,things might become clearer
What is that smartarse comment supposed to mean ? are you trying to imply that I don’t trim sideways across a wave? Are you trying to join the “Roy just surfs the whitewater straight to the beach on his Royboards” crew ??. . .
Hi Kevin,
The maximum horizontal water particle velocity for a 2 metre wave, (according to the calculator which you posted) is less than 2 metres per second. . . . which is around 4 miles per hour, maximum. . . . so even if the particle velocity can be translated directly into board velocity under ideal conditions (which has not yet been established) you are only going to get 4mph maximum, but surfboards can go at least 18 to 20 mph faster than that !!!. . . . . . so surfing is still primarily a gravity sport !!
The flow cannot push the board faster than it is flowing. . . . it is like being carried along on a river. . . you can’t just angle across it to gain speed !. . . . you can with gravity though, because you have an opposing force. . . . . that of the wave surface. . . but there is no opposing force to the horizontal flow, so the board will simply be swept along with it.
.
Roy,
That’s not the way it works -i.e. water particle velocity does not give you surfboard velocity. Water particle velocity can be used to get pressure, which together with surface area gives force. Force on the surfboard makes it move. If you do the suggested calculations you can get some idea of the forces involved.
You may not be able to exceed the forward velocity of the maximum water particle velocity of a wave when traveling in that direction, that is forward, (unless you temporarily make a drop), but you can exceed it if you angle your board and move in the down-the-line direction. This is always the case if you are not going straight (in the direction of propogation, and you’re not climbing up, kicking out, etc.), for you are traveling with the same forward velocity of the wave, but also have a sideward velocity, therefore the magnitude of your total is always greater than the forward (alone.)
Kevin
Quote:
Roy, .
You may not be able to exceed the forward velocity of the maximum water particle velocity of a wave when traveling in that direction, that is forward, (unless you temporarily make a drop), but you can exceed it if you angle your board and move in the down-the-line direction. This is always the case if you are not going straight (in the direction of propogation, and you’re not climbing up, kicking out, etc.), for you are traveling with the same forward velocity of the wave, but also have a sideward velocity, therefore the magnitude of your total is always greater than the forward (alone.)
Kevin
Incorrect. . . . the horizontal water velocity cannot drive the board in any direction other than the direrction in which it is travelling, i.e. straight towards the beach. . . unless it has an opposing force . . . . which it does not. . . . . . angling across the wave is entirely due to gravity and the opposing force of the wave face, and has nothing to do with horizontal particle velocity. . . . . the fact that surfboards do angle across waves cannot be used byitself to establish your case, and any attempt to do so is a circular and fallacious argument.
I will give an example. . . . if you are being swept down a river on your board you cannot angle across the flow and gain sideways movement relative to the flow no matter how you present your surfboard to the flow. . . . unless you have an external and opposing force which will change the direction of the force . . . . . there is no such force opposing horizontal flow, and all speed across the wave is created through gravitational force, this gravitational energy being gained by vertical water flow, not horizontal water flow .
.
Quote:
Roy,
Water particle velocity can be used to get pressure, which together with surface area gives force. Force on the surfboard makes it move. If you do the suggested calculations you can get some idea of the forces involved. Kevin
Kevin, very sorry but once the surfboard is moving horizontally at the same speed as the flow there is almost no pressure at all. … the pressure will occur mainly while the inertia of the object is being overcome, until the object has accelerated to the same speed as the flow . . . and then the pressure will become insignificant. . … this is because there IS NO FORCE OPPOSING THE HORIZONTAL FLOW… . . . . you have been trying to use gravity as the opposing force, but that’s a not possible because gravity acts at right angles to the horizontal flow and thus can not possibly oppose it !!
Pressure requires an opposing force, which you don’t have. . . . your theory just went thud as it hit the ground. . . thank god for gravity !
Quote:
To get a feel for the pressures which impacting flows can generate (that have a given particle velocity associated with them), use the quick and dirty dimensional treatment,
p = d*|v|*|v|,
where,
p is pressure in Pa (= N/squared-meter)
d is density in kg/cubic-meter (I’d go with 1000 kg/cubic-meters for water.)
v is magnitude of velocity
or in words,
pressure equals the density of the liquid times the magnitude of the velocity squared.
Kevin
The formula above is quick, dirty, and incorrect.
In order for there to be pressure, mass is required . . . .mass in movement, and some mass opposing that movement. . . . your ‘formula’ does not include mass, and sio it cannot possibly calculate pressure. . . . . you use density, which does not imply actual mass. . . . it only tells us how much volume a given mass will occupy. . . . but you have no mass in movement. . . or in fact any mass opposing that movement. . . all you have opposing the movement is area. . . and area does not imply mass either. … … .area with no mass means no pressure.
Kilograms per cubic metre is not a mass, and cannot imply a pressure at any velocity !!!
Jeez mate
!!!