dave your ready for randy
enjoy and watch the rest
Surfboards are planing craft. (Displacement) drag is vastly reduced by planing. And the thing about planing is it’s accomplished by lift. That’s really basic. As surfboards are planing craft, and most people aren’t using surfboards where you have to drag your foot to turn them anymore, it’s a given that lift and its redirection are primarily used.
You can see lift, you can feel it, you know you’re redirecting it when you do it, and anyone who’s shaped a surfboard, or even looked at one, knows they’re not shaped for drag. BTW, those are NASA’s definitions of lift and drag, but they’re also everyone else’s.
Take a look at some pictures and video of people surfing and even “stalling” … look for the spray coming out from under their board. That’s lift. Now find the drag. Kinda hard to see.
If you have a board youve shaped or are working on right now, maybe we can take a look at some pics and you can explain how you shaped it for drag’s sake? Versus lift.
It was the increase in drag, in the aft portion (tail) of the surfboard, that made the Hotcurl boards hold in the steeper waves, and provide superior directional stability, where the wide, planeing tail of a Plank would ‘‘slide ass’’, as it was phrased in that time period. The intent was to only narrow the tail, by cutting them down. The unintended consequence, was the increase in drag, which is what really made the Hotcurl boards work. The increase in drag also allowed them to ultimately go faster than the Planks, because they (Hotcurls) could stay higher, and longer, in the faster part of the wave, and tap the energy there.
The only force in surfing that a surfer can control is drag.
It doesn’t matter if the design of the board is a sheet house door to a sunova. No fins to fifty fins. Of all the “forces” in surfing(the name of this thread), the force of drag is the only force the surfer controls once in the water. What you do in the shaping room determines how you have to apply the force of drag.
When a plane is flying and hits a wind shear it can fall out of the sky. Like surfing it’s just not one force in play. The water or spray you see releasing is due to capturing drag and the water going the way of least resistance. Likewise, getting on a sweet spot plane down a wave is the release of drag. I can apply drag and move up the face with no spray at all if done slowly. Making spray is sometimes done on purpose and it is simply just another transfer of energy from one object to another done while surfing.
Your definitions are fine, obproud was misusing them and I pointed him to your correct version.
Shaping for drag’s sake? It’s done in everything in life. Planes, trains and automobiles, boats and yes even surfboards whether you realize it or not. Even drag is designed into a product when necesary. Ribbed condoms for her pleasure or maybe in your case for his pleasure.
Everything about surfing is controlled by the capture and release of drag once in the water. All the other forces are not controllable or are a direct result of changing drag. How you set your fins or shape your board allows you to optimize the force of drag for a given wave or condition. But that is a totally differnt subject
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You state"
“when you step on your tail not only are you slowing your forward progression but you are also putting more of your board surface area in the direction of the flow, creating more lift up the wave.”
Actually your downward movement on the face of the wave less than the upward force of the wave getting pushed up from the oceans bottom. Stepping on the tail causes drag. I could accomplish the same thing with my hand or a paddle dragging in the water and not changing the bottom surface of the board at all.
Drag causes this thing you refer to as “lift”? Your defintion of “lift” is not the same as janklow’s. I would just say the wave upward force versus gravity is the issue and my application of the force of drag is controlling the to forces at hand to do somthing called surfing.
So you are saying “surface area” is a force???
The only force the surfer controls is drag. Surface area is not a force. The set surface area for any given board can be used as a tool to release or capture drag by the skilled surfer.
If you want to make a contribution on this topic then you will have to write complete coherent sentences. You will have to make an argument not just repeat what you think.
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The only force in surfing that a surfer can control is drag.
If drag is the only controllable force can you explain the part the lift plays in surfing? How about the directional stability provided by the fins?
When you stick your hand in the wind, and change the AoA, and your hand moves up, how was changing the orientation of your hand manipulating the drag to make your hand move?
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Your definitions are fine, obproud was misusing them and I pointed him to your correct version.
You are going to have to explain to me how I am misusing the definitions. Which definitions am I misusing? How am I misusing them?
out
“out…”
hahahahaha!!! Not at you - With you…
Ps. ob, sharp edges do just the opposite of what you posted earlier. And, it’s not about drag, it’s about pressure differences…
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“out…”
hahahahaha!!! Not at you - With you…
Ps. ob, sharp edges do just the opposite of what you posted earlier. And, it’s not about drag, it’s about pressure differences…
Which part are you talking about?
I also think that it is about pressure differences, it is what causes lift.
"Which part are you talking about? "
I’d say pretty much all of it.
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"Which part are you talking about? "
I’d say pretty much all of it.
Wow, a complete sentence. Lets see if you can string a few together to form a complete thought.
First of all, I didn’t say anything about sharp edges. So how could what I said earlier be the opposite of what really happens, if I didn’t mention sharp edges?
Second, if you disagree with my understanding of what is happening why not explain how I am wrong? Simply stating over and over again that drag is the only controllable force doesn’t really help the conversation progress.
I am trying to understand what is happening, and I am open to understanding your understanding, but you will have to explain yourself with complete coherent thoughts.
“…reaction to the whole sped quest. . . . boys knew they were slow som started saying taht anyone can…”
learn to spell first Nemisis then maybe you can start calling stupid and unintelligent…
just a thought!
id have to agree about DRAG
this thread is a great example
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Quote:Wow, a complete sentence. Lets see if you can string a few together to form a complete thought.
I am trying to understand what is happening, and I am open to understanding your understanding, but you will have to explain yourself with complete coherent thoughts.
pearls before swine, pearls before swine,
that will do surfer, that will do.
Sorry ob - from your post near the bottom of page 6
“[=1][=Black][ 3]It is much harder for water to release from under a sharp edge on a rail of surfboard therefore give you more resistance to push against.”
The point of sharp edges is for release.[/][/]
[/]
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Sorry ob - from your post near the bottom of page 6
“[=1][=Black][ 3]It is much harder for water to release from under a sharp edge on a rail of surfboard therefore give you more resistance to push against.”
The point of sharp edges is for release.[/][/]
[/]
Sorry Taylor,
That wasn’t me. It was deanbo who said that.
I agree that sharp rails release water.
Kevin,
I’d like to get this thread back on track. I think that this is a technical discussion and that it should remain that way, i.e. using proper terminology etc. People use the term energy but I’m not sure they understand what it means and rarely state what kind of energy they are talking about.
I also believe there are people posting here who do not understand the concepts of lift and drag and appear to be too lazy to go and find the info, even when the appropriate links have been posted.
more on lift here regards the waterskier’s paradox
http://www.hullform.com/skier-paradox.html
Also regards the fact that the water is moving up the face of the wave, some have accepted this and i think at this point those who don’t should accept it and go and find the explanation of this phenomenon that suits them.
This all leads to confusing and nonconstructive comments.
So, to the Forces of Surfing.
I have finished reading the thread “surfing the force” which I think was heading in the right direction until is died for some reason. (people reading this thread should read it too)
To carry on the discussion may I quote your summary of the previous discussion…
1 The flow in the front of a wave is in the ‘up-and-forward’ direction.
2 Propulsion in surfing comes from the up-and-forward flow of the front of the wave impacting the bottom of the surfboard.
3 The direction of propulsion can be controlled through bottom presentation, for example bottom orientation with respect to the up-and-forward flow.
4 The result of the propulsion is to produce motion, down, across or up the face of the wave.
5 The motion that is a result of the propulsion, called it apparent motion, is not the source or propulsion, but, as just stated the result of propulsion.
6 Screwing with the apparent flow (the apparent motion viewed as a flow) can get you into trouble because to do so will require energy. Energy you just got from producing that same motion.
7 Fins interact with both flows; the propulsive up-and-forward flow of the wave, and the generated apparent flow. Supplemental to this is; it may be that toed and kanted fins are able to interact with the propulsive flow (by biasing exposure of their flat side to the propulsive flow and interacting with it in a way similar to that of the bottom of the surfboard. However, fins also interact with the generated apparent flow as rudders. Because toe and kant tend to work against this rudder role and likely produce some drag, its possible that the trade off is worth it, in particular given the possible boost of propulsion during trim.
8 Sleighing or basically something slippery going down a hill, is apart of surfing. But one always has to remember that a wave is a moving beast, therefore, even if you sleighing (call it what you want) you still will have to interact with the up-and-forward flow. To make a big drop (or little one) you basically orient the bottom of your surfboard such that the down-the-wave component is zero (or at least small) and that the vertical component of the propulsive force does not balance out you weight (force of gravity.)
9 The major role of foil in surfboard fins is likely to be structural (stiffness control) and functional with respect to the apparent flow. Its unlikely that they play any major role in lift.
Now with that said I believe that to close the loop the force of gravity should be added to your force vector diagram with the board in trim, and thus the resultant force can be resolved.
I still have an issue with the term ‘propulsion’ but i’m with you most of the way - i think of it as lift driving the surfer across the wave. Perhaps a diagram looking straight at the wave, like the one with ‘protesters’, maybe easier to understand and draw. Again forgetting about the toward the beach velocity might make things easier to understand.
The bit I want to get to is fins, which is where i get a little confused.
I have enjoyed your writing so far, please keep going.
There’ll be a pint of the black stuff waiting for you.
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2 Propulsion in surfing comes from the up-and-forward flow of the front of the wave impacting the bottom of the surfboard.
And what would you say, precisely, to those of us who feel “propulsion” actually comes from the wave lifting the rear of the board above sea level, causing the nose to face downwards (slightly), at which point thanks to gravity the board slides down the slope, a slope that continually (one wishes) rises up in front of the board?
MaraboutSlim,
firstly, the words you quote from my post are not my words, i quoted KCasey.
However, regarding your description of propulsion, this is how I thought of it in the beginning, purely driven by gravity and I suggested thinking of the wave as a skateboard ramp with a conveyor belt running up it.
Gravity does provide the propulsion if you just surf straight down the wave, but most of us don’t. If we talk about a surfboard trimming across a wave there must be a propulsive force pushing us across the wave. And I think this is how KCasey sees propulsion in surfing -
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this causes lift which we direct to drive us across the wave.
2 Propulsion in surfing comes from the up-and-forward flow of the front of the wave impacting the bottom of the surfboard.
I think both forces are important and need to be included to fully resolve the forces in surfing.
Phew, still wondering whether the two hours I spent wading through this thread was worth it…it wouldn’t be a “forces in surfing thread” without the obligatory glove-slapping duel being countenanced by the “gravs” against the “flows”.
Still Dr. Al I think you have provided a clear enough summary.
But one more thing for the gravs to consider : at certain very hollow waves and the one I am thinking of is Gnaraloo in WA…due to the presence of diabolical boils and steps in the face one has to ride at the base of the wave for what feels like an extraordinary amount of time to get round them…at the right time there is an incredible burst of acceleration from the bottom turn up the wave away from gravity.
This is easily observed at any hollow wave …it is common for the surfer to hang at the bottom of the wave waiting for the right time (long after the kinetic energy of the drop has “worn” off) and then by simply leaning in and presenting the rail and fins into the water flow accelerating up the face.
I would go further and say that modern high performance shortboarding in big hollow waves (which has been happening on shorter and shorter equipment) is almost the case par excellence for this phenomena.
The shorter , more manouvreable equipment can harness these extreme flows at the base of the wave so much more effectively than, say, big 'ole pintails…enabling those of appropriate skill to pull up under the lip at the last second utilising this burst of acceleration by effective board presentation to the flow to ride deeper than ever before…
Don’t know about you guys but there ain’t nothing like that in skateboarding, skiing, or whatever other phoney analogy seems to get cooked up to describe something surfing only barely resembles…when was the last time a phucking snowboarder got barrelled.
To me it seems obvious that in this case (for those who argue this has nothing to do with board design and is mere internet onanism) that actual board design (in big hollow waves and tow boards in particular) has actually changed quite dramatically and that our actual understanding is only now (through forums like this ) starting to try and grasp the phenomena.
steve