Dynamics - Relative Flows

General Discussion
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Aloha Roy

Fun stuff here!

I agree with you totally that GRAVITY and the UPWARD FORCE of the water are the major forces we harness in surfing.

But there are 2 other contributing forces which I think you tend to underestimate.

1 Gravity

2 Upward thrust of the water

2 Forward movement of the wave

3 Sideward thrust of the wave (I struggle for language to name this)

1 We all understand gravity pretty well

2 Upward thrust. You understand this well, I don’t know if it is widely understood or accepted though. Hence my description in a previous thread about the upward column or wall of water.

3 Forward thrust of the wave. I really can’t spend much more time here other then to reinforce that once the wave begins to shoal or break and depending on the original speed of the swell (which in Hawaii tends to be much faster then most everywhere else) will pitch forward with much greater speed and force then a green water swell. To be clear Roy, I am not talking about just the Lip part that one gets tubed over by. I am also talking about the waves face which is thrusting FORWARD and upward and eventually pitches over ones head. The lip is pitching forward for sure, that is easy to see but the wave face under it is hurtling forward also. Just a bit less then the previous area of face that is now the pitching lip! There is tremendous forward force here! Were one not to escape this by angling off into a part of the wave face that was just about to do the same, they would get thrown with huge force, up, over and forward! This need to angle off leads me to #4

4 This force is like putting a 12" ruler on the edge on a desk top and holding it in one’s fingers at the 1" end. Then placing a marble right against your fingers and the ruler. Then rotating or pivoting the ruler at your finger end, while allowing the marble to roll along the length of the ruler accelerating it as it is launched down along the rulers length. The faster you rotate the ruler the more force is imparted to the marble in a down the line direction. The ruler like the wave is moving toward the beach but also horizontally down the line and like the wave and rider the marble is thrust down the line into a freshly steepening part of the wave where the force of both Gravity and repulsion is increasing just as the forward and upward thrust of the wave is also increasing. We need a good name for this effect. But lack of a good name doesn’t negate its existence. Bowling waves or good points and jetty breaks impart tremendous power to the surfer through this effect. I should probably note that even without the marble having any gravitational force imparted to it, the marble will fly off the end of the ruler at great speed if the ruler is rotated forcefully enough.

Roy I don’t doubt that you have ridden some bigger hollow waves. But if you haven’t done so at Pipeline you should be reserved in your confidence of what you think that is like. I am not attacking your surfing abilities at all. But what I and others know about you is primarily from your participation here and your website. We aren’t trying to unfairly judge you or antagonistically categorize you. But seeing the waves you are riding in your videos, you have to admit that there isn’t much there that would make anyone think you have the experience or skills in your surfing or board building for places like Pipeline, let alone Hawaii in general. You could fix this easily by posting up some materials that would sway everyone into being convinced otherwise. And it would put a lot of doubters to rest. Which would be very cool! Not that you need to do so or owe it to anyone. Nor that those who do have those credentials are somehow any better of a man because of it. But Swaylocks is a virtual community where only what they know and support, what we can easily wrap ourselves around.

You make very specialized equipment that handles your waves the way you want them to. But lets not kid ourselves Roy. Your equipment, as I have viewed it, wouldn’t handle the surf we have here on the North Shore let alone set any performance records. That is in no way a slam on you or your equipment. Just reality. You have chosen your path in life and I have huge respect for how you do it.

I am not trying to over hype Hawaii, but trust me Roy, it is a very exceptional place. Not because it is my home but because it is a well known and widely accepted fact. It isn’t hype. A month on the North Shore will change your whole perception of what the complete surfing experience is. Everyone thinks they “get it” until they come here and experience it for themselves as I am sure many here can testify to. Hawaii doesn’t have the reputation it does for no reason. And anyone involved in surfing should make the trip to the North Shore at least once in their life to gain a proper reality adjustment.

Roy, we are actually agreeing here more then you think. That is why I used the example of the fire hose type column of water in a previous discussion. There are 2 forces at work in the column. 1 is lifting the rider higher to improve gravitational force. 2 is the repulsive force you are talking about. Even if that force wasn’t vertical it would still be a force available to the rider. This is like my # 4 force mentioned above. And like in a Flow Rider the force can generate huge power to the surfer. In a good, big hollow bowling wave it products a sort of twisting spiraling force that can be used in surprising ways.

Where I am drawing some difference with you is…

What exactly is the wave face? In a shoaling/breaking wave especially larger, faster, hollower ones like Hawaii has, one’s normal sense of where the wave face becomes… Lip… gets distorted. You can almost get lost on the face of a big Sunset wave and the less experienced often get pounded when they find themselves in the wrong place at the wrong time. In a stop action photo, I can understand how Hawaiian waves don’t seem all that different then other larger waves. But the speed at which this is all taking place here, seems like twice as fast as elsewhere. It is really remarkably different.

Contemporary surfers spend a lot more time in the upper 50% of the wave these days, then they used to.

Surfers are gaining a lot of power from those areas of the wave that wouldn’t normally be called the wave face. Or weren’t regularly available to them before.

The push of the forward movement of the breaking wave is more then you give it credit for. As, trying to stand in the same position on the reef as a wave passes by demonstrates. In Hawaii where that force is much greater it is very apparent. I am not just saying “HOLLOW” waves. I am saying fast, steep, big, hollow waves. Once you have ridden the kinds of waves I am talking about you will understand what the difference really is.

The down the line slinging force of the wave is greater then you give it credit for. Though I haven’t heard you or anyone else mention this before that I recall. (the marble effect)

You give 95% to the upward thrust of the water. I wouldn’t give it quite that much but it is the primary force for sure. For many surfers, that force might be the only one of the forces available to them to them unless they get better or ride more critical waves.

Whew! That exhaused me too.

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That forward force you are describing is actually the difference between the constant velocity of the upper 1/3 of the swell and the deceleration of the lower two thirds of the wave, when an open sea swell shoals. Hawaii experiences faster waves because it is a seamount in the middle of some of the longest open steches of fetch in the world. Since Hawaii has it’s unique location and abrupt bottom contours, it gets many great fast (unimpeded) waves. But, there are shores of many other locations around the world that have windows of unobstructed fetch exposure and abrupt bottom contours.

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problem: the upwave flow is going the wrong way to be called a “propulsive” force.

  1. you accelerate toward the bottom when you point your nose downward, against it, as when you paddle, and

  2. you end up closer to the beach than you started, against it, and

  3. it’s more than 90 deg off your down-the-line vector, ie you’re going diagonally against the flow

how can you say that a force that’s exerted in the opposite direction of all your vectors propelled you to your final destination?

Apparent planing speed is increased. Means that a rider going down a theoretical static grade of water would have less apparent speed and lower plane and higher drag than if there were a opposite flow under his board. Hello, Flowrider. What’s the difference between a Flowrider or riding a river wave, and surfing? No difference?

BB, I think the term would be “shove.” From the jacking, right?

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janklow it can and does get used as a propulsive force. When you bottom turn you turn against that force. When you project up the face there is less resistance since that vector is opposing gravity and the swells forward mometum vectors. And, without that vertical vector how would you get anything to bank against. Trimming in the tube is a delicate balance between all three vectors and what ever momentum the surfer can carry.

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Fair enough about the push up the wave, Tom. That flow helps. You don’t need it to turn.

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there is the flowrider effect but there is also the 3 and 4 effects outlined by BB. Finally we are getting somewhere when it comes to understanding the hydrodynamics of surfing. Thanks KC.

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Aloha Tom

What, no Transpac? I was hoping we would have a chance to get together.

Quote:
That forward force you are describing is actually the difference between the constant velocity of the upper 1/3 of the swell and the deceleration of the lower two thirds of the wave, when an open sea swell shoals.

Yup, that’s it. But I think even the lower part of the wave accelerates as it shoals. The wave form contained in the water slows and dissipates but the momentum of the water continues to thrust forward. It is just that the upper part (Lip) accelerates even more. This is why it is easy to Duck Dive a breaking wave. And would be hard to Duck Dive an open ocean swell.

Hawaii experiences faster waves because it is a seamount in the middle of some of the longest open steches of fetch in the world. Since Hawaii has it’s unique location and abrupt bottom contours, it gets many great fast (unimpeded) waves. But, there are shores of many other locations around the world that have windows of unobstructed fetch exposure and abrupt bottom contours.

Agreed. What is so different about the North Shore though, is the diversity of intense waves compressed into a short 8 mile stretch. We don’t really have an alternative here. I wasn’t trying to overly praise Hawaii, just pointing out the unique conditions here. And how it is easy to presume to understand it without having experienced it. It is always different then everyone expects.

It is relevant only because I was trying to establish that the water in waves do move forward and that some energy is imparted to the surfer because of it. In Hawaii, I think this is more noticeable then elsewhere and experiencing how hard a 3 foot wave can slam you and drag you all the way back to the beach is an eye opening experience.[:)]

Using my column of water analogy from a previous post, it would be like the spigot that the water was blasting up out of was on a mobile platform that was moved forward in the same direction that the surfer was surfing on the side of the column or wall of water. This would impart extra energy to the surfer. Just like the it could take away energy if the column or wall of water was moved in the opposite direction. The surfer would then have to use up some of his energy to catch up with the retreating wave (wall of water) he was trying to ride.

Waves that bowl up and break in on themselves like Kammieland, for example, have huge power even when small. The Left there, is super short because it hooks back in on itself, compressing the energy. Other waves that fan out as they break are often frustrating to ride because it seems the energy is constantly running away from you. Kind of like Leftovers does.

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Quote:

You make very specialized equipment that handles your waves the way you want them to. But lets not kid ourselves Roy. Your equipment, as I have viewed it, wouldn’t handle the surf we have here on the North Shore let alone set any performance records. That is in no way a slam on you or your equipment. Just reality.

Bill this is really OT but I have to respond because I disagree strongly, there are several models of board which I have posted pictures of here on Swaylocks which would handle surf on the North Shore of Hawaii very well indeed.

I won’t be coming to Hawaii any time soon but I am prepared to send a board or two over if anyone is prepared to pay the freight., and to make that board (or boards) available for testing at pipeline and elsewhere.

You really have no idea . . . time to get educated !

As for my surfing, just because I am currently riding small waves does not mean that I haven’t ridden bigger hollower waves, if the surfing of sways members was to be judged by video footage then I have to say that most members don’t surf, including yourself ! That would be ridiculous… . … . so lets not go that way, just realise that I have been surfing for 42 years, and have only had a video camera for 3 years, during that time I have tended to ride small waves because I have lots of little people to look after at the beach, and I don’t like to endanger their lives by letting them swim and surf when it gets big. From the previous 39 years of surfing I have one photo, that’s it. . . but I rode plenty of bigger hollow waves.

.

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Oh, I’m coming. I just don’t start until Sunday. You can track us here: http://trackinfo.fistracking.com/TP2007/ I’ll be on Rag Time in Div. 3.

As an open ocean swell shoals, the bottom of the waves energy (below sea level) meets the resistance of whatever topigraphical feature it runs into. This drag causes the longer lower open ocean wave length to bunch up or shorten in wave length and increase in amplitude. If the bottom contour that the wave runs into is fairly abrupt and not gradual more of the leading portion of the wave’s energy gets converted into height, than the rear. So, water ahead of the wave rushes toward the wave to increase that amplitude. Places like Pipe Line and Teaho poo end up with almost no increase from the back and it all comes rushing up the face often sucking the reef dry while the following mass of water and energy creates far more force than a similar waves that meets a gradual rising shoal. The more abrupt the feature the faster the bottom decellerates the more amplitude is created and the more the lip pitches due to the unimpeded upper and following portion of the wave.

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Quote:
SNIP

Apparent planing speed is increased. Means that a rider going down a theoretical static grade of water would have less apparent speed and lower plane and higher drag than if there were a opposite flow under his board. Hello, Flowrider. What’s the difference between a Flowrider or riding a river wave, and surfing? No difference?

Aloha Janklow

The difference between a Flowrider and a real wave, is that the real wave is moving relative to the land. So if you could put the Flowrider on a truck it would get more similar.

Then if you could also variably change the Flowrider’s base shape to tweak the wave shape, to form another wave that would move across from left to right like a jacking peak wave or the repelled swell that crosses a swell line next to a jetty break you could have a near perfect real wave simulation. Allowing the wave to hook in on itself sometimes and fan out other times would create similar real wave challenges.

BB, I think the term would be “shove.” From the jacking, right?

That is as good as term as any.

I have always thought it would be cool to put a 20’ diameter by 50’ concrete pipe in a skate park that you could skate into and out of. But not just statically sitting there but on rollers so that the pipe would rotate slowly and allow skaters to gain altitude inside the pipe and be able to absorb energy for use that they wouldn’t normally have. If the shape and tilt of the pipe could also be altered all kinds of cool stuff could happen inside.

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Bill, I don’t think the net effect would be that impressive on that pipe. There’s not that much to do in a pipe. Plus the resistance on the off side would fuck you all up. Anyway, dig this Bob Burnquist video here: http://www.youtube.com/watch?v=6PR-RC5Z2Sw&NR=1 He’s a regular foot, so this is interesting (!!!).

http://www.youtube.com/watch?v=BDla-x-l4Hc

BONUS: Danny Way: the second half of this clip is what youve been waiting for:

http://www.youtube.com/watch?v=5aosZJYFbnQ

Danny Way and Bob Burnquist… manly men.

I have a fee ling that Flowrider’s flow rate, if you could possibly have a surfing wave with those upwave flow rates, you’d be able to get just about as much done trying to surf that wave as you can on a Flowrider. Any idea what Pipe’s upwave flow rate is?

EDIT: not knowing what either one of those rates are, I’m shooting in the dark here–well, anyway the Flowrider and river-surfing I’ve seen look absolutely different in terms of what I can see of those upwave flows.

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Quote:
Quote:

You make very specialized equipment that handles your waves the way you want them to. But lets not kid ourselves Roy. Your equipment, as I have viewed it, wouldn’t handle the surf we have here on the North Shore let alone set any performance records. That is in no way a slam on you or your equipment. Just reality.

Bill this is really OT but I have to respond because I disagree strongly, there are several models of board which I have posted pictures of here on Swaylocks which would handle surf on the North Shore of Hawaii very well indeed.

Roy I am sure some of your boards could comfortably ride some North Shore waves, like Chuns. I was just pointing out that compared to how you praise your boards, their perfomance here won’t set any records or live up to the expectations you have built up for them.

Of course, there might be some who agree with your perception of your equipment and will buy those designs of yours so they can tackle some huge North Shore monsters. Please let us know if that every takes place so we can check out how they work here.

To be fair, I don’t think market forces are necessarily a fair way to determine the veracity of the performance of particular designs. But on the other hand consumers will quickly gravitate to things that have a proven track record. So consumption can be a marker for the success of products. Just as a lack of consumption can also be for the opposite.

I won’t be coming to Hawaii any time soon but I am prepared to send a board or two over if anyone is prepared to pay the freight., and to make that board (or boards) available for testing at pipeline and elsewhere.

To bad you can’t visit Hawaii. It would better balance out your view of thngs.

Plenty of different designs show up on North Shore every winter, but very few of them survive the initial testings. The thrashing one takes here when they don’t make a wave is extreme and often dangerous on a “you can die” type of level. So it is no wonder that people gravitate quickly to what works and away from what doesn’t.

Additionally, the crowds are competitive beyond anything most have ever experienced. Comprised mostly of the best surfers from all over the world the surfing level here raises the bar very high. It is like a surf contest being in town all winter long. Because of this, every wave is required to be surfed at its best. And if the crowd judges a particular surfer or board to be not using the wave to its ultimate limit, that surfer will find it hard to get another wave as others who feel they will utilize the wave better will simply take it away from them. I am not saying this is right… just pointing out the realities. And of course there are exceptions and a few less crowded days or less intense crowds.

The board designs that are commonly used here are highly evolved for this environment and it isn’t easy to interject vastly different looking boards into the crowd and get any courtesy from them to test it out.

You really have no idea . . . time to get educated !

As for my surfing, just because I am currently riding small waves does not mean that I haven’t ridden bigger hollower waves, if the surfing of sways members was to be judged by video footage then I have to say that most members don’t surf, including yourself ! That would be ridiculous… . … . so lets not go that way, just realise that I have been surfing for 42 years, and have only had a video camera for 3 years, during that time I have tended to ride small waves because I have lots of little people to look after at the beach, and I don’t like to endanger their lives by letting them swim and surf when it gets big. From the previous 39 years of surfing I have one photo, that’s it. . . but I rode plenty of bigger hollow waves.

I don’t doubt your surfing history Roy. And didn’t mean in any way to disparage you, your boards or your surfing abilities. The problem with your strong sales pitch Roy is that your boldness and confidence is only testified to by yourself and that makes it hard for people to embrace it the way you would like them to. Especially since what you are bringing to the table is so different. This causes everyone to cry out for verification yet they aren’t able to find it. If you weren’t so confidently saying your boards were exceptional and even able to perform on the North Shore “very well indeed”. And that the rest of us were all somehow blind to this and missing out on the revelation you would like to bring to us. Then you wouldn’t be getting so many challenges.

The surf industry can be retracted, slow to move, too conservative, and socially stagnant to the point that good things don’t happen as fast as they should. But in the end, it keeps progressing forward somehow!

I wish you well Roy and get a huge kick out of your whole lifestyle and your board designs. Maybe one day I will be riding your designs and saying what an idiot I was to not get on them much earlier… And then maybe not![:)]

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Quote:
Bill, I don't think the net effect would be that impressive on that pipe. There's not that much to do in a pipe. Plus the resistance on the off side would fuck you all up.

Aloha Janklow

I wasn’t thinking of the Concrete Pipe in skating terms, but rather in surfing terms. So that you could work down the pipe pumping on the rising wall like one does in surfing. Not to stay and play in the pipe but just as a small section of a whole skate park. Imagine it rotating faster, maybe when I said slow it sounded like I meant slow and boring. You enter, work your way through and out leaving room for the other guys behind you. Not like a static half pipe but like a tubing wave… horizontal movement and speed gained from little effort due to the rising wall.

Anyway, dig this Bob Burnquist video here: http://www.youtube.com/watch?v=6PR-RC5Z2Sw&NR=1 He’s a regular foot, so this is interesting (!!!).

http://www.youtube.com/watch?v=BDla-x-l4Hc

BONUS: Danny Way: the second half of this clip is what youve been waiting for:

http://www.youtube.com/watch?v=5aosZJYFbnQ

Danny Way and Bob Burnquist… manly men.

I didn’t see anything like my rotating pipe on the above video. Did I miss something?

I have a fee ling that Flowrider’s flow rate, if you could possibly have a surfing wave with those upwave flow rates, you’d be able to get just about as much done trying to surf that wave as you can on a Flowrider. Any idea what Pipe’s upwave flow rate is?

That’s an interesting question! Having ridden both a flowrider and Pipeline, I can tell you that the rate of flow is extreme in both cases. And probably similar in MPH. But I don’t know what either are. That would be a great college project to measure the upward flow rates of various waves.

The big difference between them is the amount of wind coming up the face at Pipeline where as the Flowrider has none. The only way you get wind velocity up the face is from the water moving forward rapidly not just upward. Add some offshores and you have a whole new challenge. Of course, the wind holds the wave up better so there are advantages along with the challenge of piercing through the wind and not getting hung up in the Lip.

EDIT: not knowing what either one of those rates are, I’m shooting in the dark here–well, anyway the Flowrider and river-surfing I’ve seen look absolutely different in terms of what I can see of those upwave flows.

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Re: my statement about the off wall–if you’re carving and pumping through, one side of the pipe is very much not your friend. Not even talking about the side with the assist. The downward rotation side side ruins your run on your first turn against it. There’s really nothing to be gained by adding mechanical rotation. Even in your head.

The vids : Andy Irons would wet his queer little shorts if he looked down the ramp Danny Way is launching off.

PS: Don’t take that the wrong way, Andy.

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Urm… Please excuse my ignorance and I am most certainly not taking sides… Having too much fun watching :smiley:

But out of curiosity…

Why is Hawaii more valid than Indo?

Geographically and financially speaking it would make far more sense for Roy to go Indo (cultural differences aside).

And before the screaming starts - yes I know there’s some difference (e.g., pipeline) but with a boat and considering the majority of breaks…

OK, diving for cover now. Don’t expect me to respond to abuse :wink:

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Any Takers Please?

Reading the Wake

I’ve tried the ‘wake’ approach before, and it didn’t seem to go over too well. Nevertheless, I would be interested in someone else’s interpretation or analysis of the wake in the picture below. The full picture can be found in the ‘Letter to Bill Barnfield’ thread, posted by easternpacific. I just enlarged the area of interest.

As to how to characterize what state this fellow is in, other than critical, that is to say he is neither dropping nor climbing is probably a bit too risking. To me however, this much seems likely, if he drops much further without pulling out in from of that lip, he’s likely toast. My guess would be that he really isn’t dropping but trying to maintain a certain critical vertical position, which is likely to change a bit from moment to moment. That is, he’s not likely to be looking to make a bottom turn or start to climbing in the very immediate future – but who knows, it’s a snapshot, and things can change rapidly.

If you do decide to weigh-in on this, please include an explanation of the shore-side lateral fin shadow. There’s also the leash wake, but if you look closely you can see the fin shadow, or maybe not. It’s not the best fin shadow, and if this turns out to be too controversial, I’ll post some other shot(s) in which the fin shadow(s) are clearly present under similar (surfing) circumstances.

I guess you can make your own guess as to his fin setup, but mine would be a pretty standard toe-canted tri-fin, but again I simply don’t know that for sure.

There is also that curious fact that the shore-side wake is different from the ocean-side wake, the ocean-side wake almost ‘curling’ in on itself. And of course the direction of the spray leaving the shore-side rails.

The purpose of this exercise is not to surprise ‘takers’ with my keen, yet undisclosed observations and insight – I really do want to know if I’m alone in my appreciation for reading wakes. If you look at a lot of snap shots of surfing wakes certain common themes do emerge, well at least in my opinion. You could also watch wakes first hand – but trust me, becoming to engrossed in your own wake can lead to problems (rumor has it that Janklow went temporarily blind, oh wait, that was from another type of engrossing, …sorry Greg, had to pinch that off) – but you can always take a glimpse at the wakes of others.

Anyway, the point of the exercise is to get as much information about the movement of water under the surfboard as possible, on the cheap so to speak.

kc

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Waves are waves. Obviously waves like Pipeline and Teahupoo are considered some of the fastest waves. Any wave that travels far through deep unobstructed water before it hits a reef will have a lot of power and speed.

This issue is whether the flow of water up the face is of any significance. It doesn’t matter if the wave is Pipeline or San Onofre, because they are both surfable.

I’m not going to say, but instead give some homework to anyone that is interested.

First, study this illustration of what a water particle is doing:

http://www.crocodile-clips.com/absorb/AP4/sample/media/DJFPh063waterwave2.swf

Understand that this animation is a deep water wave. I don’t have an animated example of a wave hitting a reef, but the only difference is the amplitude of the wave increases abruptly when hitting a reef and the water particles on the top portion of the wave detach from the wave and are pitched forward. This is the lip part of a breaking wave.

Understand the difference between the wave and the water particles. Some tend to make these one and the same, but they are separate. I’m not going to go into detail, but the wave is the energy and is not influenced by the water, however, the water movement is influenced by the wave. In other words, the water needs the wave more than the wave needs the water.

Now observe a real wave breaking (some big shorebreak is good), or watch a video of some powerful waves. Pick a object moving up the face of the wave, like a patch of foam or a piece of driftwood. Observe the speed it moves on the lower part of the wave, and then the upper (where the wave goes past vertical).

Also, while you’re at it, observe how fast or slow the wave increases in amplitude right when it hits the reef. And try to see if an object on the face of the wave is moving faster or slower than this.

I’m interested in everyones findings.

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Mesmerizing animation – thanks.

Deep water waves are definitely somewhat different beasts than rapidly shoaling and/or breaking waves – the trajectory or path of the water particles changes, as do velocities, but until shearing actually occurs, the overall cycle, at least in terms of the direction of motion of the water particles remains characteristically similar.

The terms wave or waveform propagation speed and forward water particle speed can be abused, as was more or less pointed out to me in a prior post. Nevertheless, as the wave moves towards breaking, in particular during those moments directly prior to breaking, the difference between forward water particle speed for progressively larger regions on the face of the wave, with that of the waveform propagation speed –i.e. the term refers to the waveform as a whole - becomes progressively smaller. In fact given the decelerating nature of the shoaling waveform, some, as in the ‘pitching’, at least shearing portion are actually moving faster than those in lower portion of the face – hence the shear, or ‘break.’ Of course, propagation speed as used here still refers to the waveform as a whole, and not merely the simple average speed of a collection of individual water particles exhibiting a range of speeds.

There is of course changes in height which will occur with shoaling, which definitely has an impact on water particle velocity – water particles having to negotiate paths of increasing height in roughly similar times, and this change will continue until shearing occurs (I guess that’s obvious.) The precise nature of all these changes is a function of the properties of the incident waveform and bottom geometry.

Things are also changing below the surface, in a somewhat similar manner. Though there may be a significant difference in their kinematics, at average ‘fin depth’, water particles are likely moving in a similar fashion to those found nearby at the surface. (Though I’ve often wondered if this is a completely reasonable assumption when considering some of those really ‘deep’ fins, or maybe not so really deep fins.)

In a nutshell, as the waveform rapidly shoals, vertical water particle speed increases, and the difference between forward water particle speed and waveform propagation speed diminish. At least that’s my rough picture, the whole thing adjusted for a given waveform-bottom geometry interaction.

A Couple of Comments

The literature is ripe with reference to the wave as ‘transport of energy’; in particular, that there is an insignificant net motion of water as the waveform passes by – which is true. But ‘surfers’, aside from geeks and weanies, of which I include myself, are generally only interested in the leading face of the waveform – half the cycle, you might say. It is only over the full cycle that net flow is negligible, but when you’re only dealing with the leading half, not so – the flow is real. Surfers really don’t participate in the restorative forces involve in shaping the waveform - they harvest their outcome. The only interaction they get to have with the waveform is via flow against solid hard thing (or solid soft thing, like a matt for instance.) Gravity of course plays a big role in assisting the surfer to take advantage of the interaction, and do some other fun things too. (That stated, its not really true when you start to consider some of the other associated activities that surfing includes, in particular duck-diving. Another thread perhaps?)

Anyway, the point I would like to make is that it is the total flow against the bottom of the surfboard and the respective orientation of that bottom, that makes a surfboard go.

Okay, you can use a surfboard as a sort of gravity sled by skimming down the face like a flat stone, but the fundamental force in surfing is that of flow against a hard thing – the transfer of water particle momentum to surfboard/surfer.

Interesting post and request – I enjoyed that.

So, tit for tat? Please consider taking a shot at my request above (post to Janklow) regarding ‘reading wakes’ - if you’re so inclined. I know I’d be interested.

kc

Ref: http://www.waveenergy.dk/

59

KC, I’m going to answer you out of respect for the fact that you called me out in a friendly enough way, but I’ve really spent too much of my life on this project already, last year. It didn’t win any of us any friends and I obviously didn’t change your mind, and it was a waste of time because it didn’t advance my understanding of anything–it was simply an attempt in vain to explain something I think obvious to someone who has his mind made up already.

The answer is, and I won’t bother to gather photos online to prove it, that a snowboarder descending a slope of the exact same grade would be leaving basically the exact same wake of snow and spitting the same Newtonian spray off the non-engaged side of his board. And a waterskier with his body in the same angle to the surface of the lake surface as that surfer’s is the wave face behind him would be leaving a similar trough and spitting a Newtonian spray (EDIT: actually much bigger ones, given the speed he would have to be travelling to make a turn with that angle) off the non-engaged side of his ski.

etc.

The wake seems to be curling over itself, you say.http://www.grc.nasa.gov/…Images/downplane.gifNot to mention gravity, hey?

60

Greg,

The post was in reply to you, but also anyone else who cared to make the analysis. No offence meant, hopefully none taken, as for the rub, or my attempt at one, same thing.

Your interpretation is fine with me, mind you, I disagree with your interpretation, close to completely, but it’s not like that ‘automatically’ means you’re wrong.

As for going over this again, things evolve, and details perhaps not seen or appreciated before might appear and lead to further innovation, this is particularly true for ideas. Waiting for the sparkling new notion to simply show up, or independently present itself, here in this forum, or anywhere else, is becoming more of a loosing proposition by the day, hell, by the moment. If you thinks its all flat-rock skimming, then build sleds and the hell to the rest of the nonsense. That others, me included, disagree means jack-shit - experience is king, and that incudes your personal interpretation of it.

kc