What Makes Surfboards Go

General Discussion
81

…Lame…

The super smart people must know how to take photos…You are super smart and you must have super stuff like cell phones…and I Phones…and high tech spy photo tech…

…So you go on and on about super stuff with no surfing photos and nothing…nothing…please use all your  brain power…and post some photos…maybe some photos of why your stuff is better / different.

…not youtube stuff of someone else…maybe some photos of you surfing with your super ideas…super surfboards made from super ideas!

Maybe you guys can get some photos later and play bingo in the trailer park…after your nap.

82

I reckon that by continuing with this topic we are running the serious risk of breaking the internet. 

83

hey Bill thanx for the reply, have to roll that one around with the marbles for awhile. I do think you’re onto something there. But I keep picturing the weight / momentum of the surfer as an opposing force to create the sail / keel effect.

84

So, it is not actually called Newton’s Law of Universal Gravitation (aka Newton’s Law of Gravity).  It is really called Newton’s Law of Universal Weight (Newton’s Law of Weight).

Boggles the mind…

85

If Gravity were the only force at work we would take the drop and not be able to surf up a wave more then the original energy. If it were only gravity then you could not surf a relatively flat wave 
Yet you can ride a wave smaller then one foot for a very long distance on the right board. Gravity plays a part as it does in everything we do. But it is the energy passing thru the medium of water that allows us to ride ride a surfboard. Without that energy meeting resistance creating a up welling in the ocean surfface there would be no surfing. Try riding a 6 foot wave that is in very deep water say 90 foot you have a face of 6 feet and yet the " Gravity " does not allow you to drop in, why? It is due to the lack of concentrated energy.

86

this

87

Primarily, steepness of slope.  Add in paddling velocity, wave velocity, take-off velocity, drag…

I never said gravity is the only factor, just the principal factor.

Without gravity (or is it weight?), there would be no ocean waves at all.  The water would not go up and then back down, or break.

See my first post (#2).  There are many “contributing factors” as well.  Not the least of which is (for Melikefish) centripetal force.

As I indicated in my response to Mr. Huck’s deleted post, I have no more interest in endlessly debating this topic and semantics than Mr. Huck does.

If you want to get spiritual, you could say you are tapping into the “Universal Force” (Gravity).  Or maybe call it harnessing “The Force.”

88

Without gravity there would be no universe, there would be no earth, there would be ocean and no waves. You wouldn’t be able to sit, or stand or walk, let alone surf.

It is a constant force which explains why objects with mass have weight.

Its usefulness, with regard to explaining "what makes surfboards go’, is encapusulated in the single variable of the riders weight. It is as useful at explaining “what makes surfboards go”, as it is at explaining “what makes people sit/stand” or “what makes people walk”. It is absolutely necessary, but it is just not a very compelling part of the equation or explanation, with regard to this discussion.

89

I would say that makes it a fairly significant “Force.”  Mass is a component of all forces.  Divide each force by mass.

“Without weight there would be no universe…”

Absurd semantics?

Newton’s Law of Universal Weight?

LMAO

90

kcasey

I think my criticism of your analysis may stem from the following…

“The inclined surface is now the face of the wave, the water moving both upward, as well as** forward**.”

I agree with all aspects except the forward part

please explain in more detail. (diagram maybe) as I may be misinterpreting.  

91

Assuming surfer going straight down the wave 

when the body is not accelerating  

Mgx = Fdviscous+Fpx

Mgy = Fpy

There is nothing that is adding force in the direction of travel other than gravity.  

FP = planing force 

x is the direction of travel (parallel to water)

Mg  = mass x gravity

Tau is angle of attack

Fdviscous is viscous drag

I’m not super confident in my diagram on the left, it is supposed to be the instantaneous velocity of the surface water partical.  based on stoneburners wave animation posted earlier.  albeit for a  decelerating wave. but it makes sense from watching the dots and intuitively from what a wave feels like

Afterthought…

there is clearly a centripital force component  I’m leaving out associated with the velocity direction change  when moving in different locations of the wave…let me think on this more.

 

92

Below is a series of quick diagrams I made for some other thread.  

The veiw is an almost top-down view of a board on a wave. It’s somewhat over simplified in that there is an assumption made about the flow, its not a very good 3-D depiction, as such the board doesn’t appear to be foreshortened or rotated about its center line (tilted) in the drectopm of the transverse component of its assumed motion (to the right of the viewer of the diagram) as well as other problems. But hopefully it will do for purposes here.   

The point here is that Savistsky’s diagram is for a cross-sectional strip in the plane of a flow.  (Here the changes in flow that are present transvesely along the wave-face are not accounted for either, as just one strip is shown.)  Nevertheless, you can see (hopefully?) that the forces of planing do not require the board to be moving just down the face or in the direction of the wave-form’s motion, they can be redirected by the surfer via changing the presentation of the wetted-surfaces to the flow. For  example, angling slightly to his left or right, the force of planing following his lead. Angling forward or back, etc. or any combination. 

Viscous forces (that is frictional forces) do play a role, and are important, but their magnitude (in this case) are significantly less than the forces of planing, and given the broad overview of the original post, I chose not to introduce them, but introducing them would not have changed anything other than to make the treatment more complete - but then there are other frictional forces that might arise, and other forces in general which are likely to be present too.  (It was a post not a dissertation,) 

 

 

 

 

93

Why do you state the viscous forces are significantly less than pressure forces?

94

Under the conditions that are relevant here (those set by my original post), I’ve implied and assumed that the frictional forces are significantly less in magnitude then the forces generated by planing.  I admit, at least in the post that I think you may be referring to, that the model I’ve proposed would appear to be an inviscid one, in as much as I only mention in passing that there are other forces at play.  The model which I wanted to convey is one that establishes the connection between the exchange of momentum between the flows involved and surfboard, and how the surfer can redirect the forces generated by that exchange. 

Whatever the case, and though you haven’t implied that I have said as much, I am not saying that viscosity is insignificant.   I just didn’t see the point of introducing viscosity at this point.  Viscosity and in general frictional considerations can be important surfboard design, but the original post attempts to broadly set a stage where such design considerations can be introduced.  (I guess what I’m saying is you have to start somewhere, and I believe establishing the role of planing was a good place to start. But if you are convienced there is some other force that a surfer taps into that allows him/her to travel transversely or trim in a barrel, great, I’d love to read it.  What I write isn’t exactly gospel.)

95

KC, the thing about forces is that if you selectively leave a few out the whole thing falls to pieces. It’s fine to try and simplify things, but the forces do have to balance, focussing on primary elements is okay, but you missed out anything pointing to the left!

96

I think I get your point. 

But what you written isn’t true about what I’ve written, and that was my point. With a solid base, the rest becomes ‘additive’.  I don’t see anything falling to pieces by the inclusion of viscosity at some later point, nor the inclusion fins, bottom contours, etc… And the forces don’t have to balance - equations do. (Unless your trying describing the Universe, which I’m not … it’s just about surfing.   Modern medicine doesn’t account for the gravitational pull of Jupiter on the developing embryo. So I guess there’s something to be said for Astrology. … Really??)

This introduces a principle, (not as well known as Occam’s razor, but still a valuable one).  Whatever the hypothesis that your describing, its value increases if it’s extensible. And by extensible, I referring to what other hypotheses  naturally drop out of it, or are consistent with it, or other phenomena it helps to explain.  Here (see orignial post), why plan-shape matters becomes immediately apparent, as it speaks to the amount of force that can be generated for a given set of conditions for a given wetted-surface, as the planing force is roughly proportional to the total wetted surface and the speed of the flow squared, and the design of the plan-shape speaks to how efficiently the surfer can use it to control that force, etc., and how much he might need under a given set of conditions.  Similarly, for rail design (see “Rails Plane” thread). And together with the thread “The Decelerating Wave-Form”,  for the toe and cant of fins, as well as rocker and plan-shape, rail design, bottom contours, etc…   

Like I said, I get the point of you’re last post, but again, I just don’t think it applies here.  That I’ve not accounted for everything, and that’s somehow a problem? Come on.  It’s a “post”, a “thread”,  if I made it any longer in an attempt to be complete, (and please, I don’t wish to imply that I could be ‘complete’) even fewer people would have read it, and among them, even fewer would have replied.    

But here’s what I’d find very interesting, somebody explaining, using these “climbing and dropping”, “skiing down a hill”, “block sliding down an inclined plane”, “sleighing down a curved surfaces”, etc. theories,  how a surfer is able to travel transversely when getting barreled (and surfers can spend a lot of time in the barrel),  or nose-riding, for that matter.  Now that would be interesting.   

97

The board is angled downward and at a position where the slope of the face is very close to 90 degrees (wave face straight up and down).  However, I am sure somebody will post a picture of somebody temporarily surfing level with the water surface, e.g. in the trough just prior to turning into the wave face to climb.

I have done no calculations.  But, my gestalt is that the surfboard becomes a moving inclined plane as the wave face approaches a 90 degree angle to the water surface.
 
98

How does a moving inclined plane somehow allow a surfer to move transversely while maintaining the same position on that plane. He can only move transversely if he continues to drop through the gravitational field.  What you appear to be proposing is akin to the belief that you can move transversely across a hillside at the same level on the hill while skiing - it just isn’t going to happen unless you’re just burning off acquired kinetic energy - you will come to a stop at some point. Being buried in a barrel, doesn’t give you much room to drop and climb. And if your buried for anything more than second, you’ve probably blown off all of any acquired kinetic energy you may have had prior to being buried. (And some surfers get some pretty ridiculously long barrel rides.)

There was a fellow named Roy who no longer posts on this site. Roy made unbelievably beautiful wooden boards, the man was a remarkable craftsman. He also had a theory that the wave was some sort of conveyor belt of water and this allowed a surfer to both drop and climb simultaneously. (And he wasn’t alone in his beliefs.)  Presumably, this climbing and dropping occurred at a such a high frequency that you wouldn’t notice it - kind of like the way you don’t notice the blinking of fluorescent lights (my words not his.)   I liked Roy, but his theory was physical nonsense. 

We have a well known phenomena, it’s called planing, which is just another name for an exchange of momentum, and an exchange of momentum results in a force. The surfer is able to control the result of the exchange in momentum between the board and the flow to a large degree, which includes its direction, which allows him to use that force to move transverely.     

99

The surfboard is angled down.  The upward moving water continously maintains the board at a position near the 90 degree angle area of the face, assuming the surfer is maintaining the proper angle of descent.  The downward pull must be greater than the upward push.

It would be more like the earth of a mountain slope continously moving upward as the skier slides down. Skier downward motion must be greater than earth upward motion.  Visualize the upward moving water in the cruise ship wave/surfing machines.  

IMO the tail, rail and fin are what keep the board from free-falling when the face is close to 90 degrees. Moving transversely accross the face creates the angle of descent for the moving inclined plane.

All the while, the wave face is still moving forward toward shore.

Not looking for an arguement.  Just my thoughts and $0.02.

100

The waveform is moving forward, and the water is moving up (mostly). 

Kind of like if you moved your finger along the bottom of one of these toys (it is not quite this simple, but more like this than a conveyor belt): 

So when a surfer is in trim, the pressure/lift/planing from the upward moving water is perfectly balancing the weight (i.e. gravity… for stoneburner) of the rider, so the rider doesn’t move up or down the wave. But the wave form is moving forward (forward moving inclined plane) at the same time, pushing the rider along.