Is it possible/likely that your original subject title “Bottom Contours - Less is more” is inapropriate?
I dont see the relationship between bottom contours on surfboards and your discussion with respect to ‘propulsion’.
I normally dont get into those types of discussions (and often glance thru lengthy posts - sorry got a kid to raise) and prefer to stick to board design and effectiveness of said. I tried.
I agree.
If you scroll back (and I don’t think its worth it) I state that my interest is in propulsion and that if your’s is too, visit Dynamics - Surfing the Force.
Nevertheless, its hard to justify doing something to the bottom of a board unless you know where propulsion is coming from. Then again, if something worked for someone else, why not just try it.
My original post in this thread has my thoughts on bottom contours, and currently ‘less is more’ sums it up. I believe this because of experience, and what you’d find in the Dynamics-Surfing the Force thread.
Here’s a summary:
The propulsion is coming from a flow which is up and forward.
This tends to produce a rail-to-rail flow.
Propulsion produces the nose-to-tail flow, and screwing with it can get you in trouble, that is its a consequence of the actual propulsive flow, not the flow producing propulsion.
I have dealt with fins yet.
Kevin
Some nice ideas and models.
So how do we accelerate up the face (out of a bottom turn, for instance)?
It’s not all momentum, because it’s possible to enter a bottom turn with almost zero speed, yet still accelerate.
It’s not water dragging up the face, because we go faster than if we just floated up the face.
It’s not gravity because we’re moving uphill.
The surfer must supply (most of) the energy. Pushing the rail of the buoyant board under water; redirecting water flow from it’s uphill course to across the bottom deck…
Upon reflection I think that (1) is an incorrect assumption/observation and it’s probably a combination of the converse of 1+2(+3?)+4
ive got to throw this in there since this is such an intensive thread on coutours. what i have noticed is that the concaves don’t seem to do squat unless one is surfing in absolute glass. with any surface bump on the water, the water just doesn’t funnel down the concave with any efficacy. with that in mind are we really acheiving a benefit or just creating more drag and disruption of flow? it just doesn’t seem like we surf that much glass…usually offshore or onshore.
secondly, when one does have glassy conditions, concaves seem to require a very specific sweet spot stance where they will work. shuffle your feet a hair and the concave benefit disappears. all in all, the only millisecond i notice the difference between a concave and nonconave board is on a burried nose to tail bottom turn or cutback. Anyone else share my observation. andy irons would probably tell me im nuts.
Less is truly more in bottom contours; at least from my experience. Subtle and blending are the key words, and a good shaper will give a lot of consideration to the 1/8" glass that will produce the final contour. As far as the technical discussion goes, everybody is sized different (particularly feet) and each wave is very different. Because you can’t replicate in the lab the exact field conditions (the random stuff), you cannot really do design modeling and formulate hard design parameters. Well, not unless you can alter the shape of board in response to the water movement using some kind of fuzzy logic control maybe. But then you’re not really riding or controlling the board anyhow. Until a person becomes good enough that they can ride any type board really well, I don’t think they really can’t make an accurate judgment on 1/8" more Vee in the tail or not. Many of us fall into that category, and we often select generalized bottom contours based on what works for us at a given break. I’ve got some boards with dead flat bottoms, some with all sorts of concaves, and I’m still fooling around with tail channels/single fin setups. Ranking design features by order of impact would be: Outline (mainly length), thickness, rocker, fins/rails, and bottom contour last. Well, that’s how I do it at least.
Very interesting. You hear a lot of speculation about exactly how water moves under the bottom of a board. Again, it has never been measured so nobody really knows what goes on under our craft. There is plenty of speculation, listen to what some channel bottom riders reckon. Apparently these boards often defy laws of physics such as the conservation of energy. I know they go well and blokes like Al Byrne understand what goes on down there, but SHOW ME THE DATA. Water flow is another aspect of board design I would love to bash with a big science budget to try and blow shackles, but as you said it will probably never happen as the cost/benefit scenario does not compute (maybe).
One thing I would like to do is build a board full of sensors that would measure heaps of stuff in real time. Here’s how it works;
On the deck are pressure sensors that dynamically show foot contact and pressure, like those pads at The Athletes Foot shoe stores where they tell you if you pronate when you run. You then place a number of minute swivelling “flag” sensors under the board to measure water direction and speed. You then have piezo electric sensors in the glass to measure flex. You then film a person surfing the board while dynamically accumulating the data. On a screen you see the surfing, a dynamic colour coded foot pressure gradient graphic, a dynamic flex graphic and a dynamic water flow graphic. This setup could also be used to analyse surfing technique and assist coaching. “Oh mate, you are putting way too much front foot down at the end of your turn” etc etc. Maybe we could blow the lid off how Slater does what he does?
You could then watch Slater surf and watch exactly what his feet do, how the board flexes and exactly what path and speed the water takes under his board. Would be interesting and quite revealing I reckon.
If I win lotto I am going to go sick on this and my other surf/science fantasies. Until then, I remain your humble Little Aussie Battler.
Very interesting. You hear a lot of speculation about exactly how water moves under the bottom of a board. Again, it has never been measured so nobody really knows what goes on under our craft. There is plenty of speculation, listen to what some channel bottom riders reckon. Apparently these boards often defy laws of physics such as the conservation of energy. I know they go well and blokes like Al Byrne understand what goes on down there, but SHOW ME THE DATA. Water flow is another aspect of board design I would love to bash with a big science budget to try and blow shackles, but as you said it will probably never happen as the cost/benefit scenario does not compute (maybe).
One thing I would like to do is build a board full of sensors that would measure heaps of stuff in real time. Here’s how it works;
On the deck are pressure sensors that dynamically show foot contact and pressure, like those pads at The Athletes Foot shoe stores where they tell you if you pronate when you run. You then place a number of minute swivelling “flag” sensors under the board to measure water direction and speed. You then have piezo electric sensors in the glass to measure flex. You then film a person surfing the board while dynamically accumulating the data. On a screen you see the surfing, a dynamic colour coded foot pressure gradient graphic, a dynamic flex graphic and a dynamic water flow graphic. This setup could also be used to analyse surfing technique and assist coaching. “Oh mate, you are putting way too much front foot down at the end of your turn” etc etc. Maybe we could blow the lid off how Slater does what he does?
You could then watch Slater surf and watch exactly what his feet do, how the board flexes and exactly what path and speed the water takes under his board. Would be interesting and quite revealing I reckon.
If I win lotto I am going to go sick on this and my other surf/science fantasies. Until then, I remain your humble Little Aussie Battler.
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I’ve stated this before, so apologizes in advance to anyone who has read that as well. But since there is at least one other person now who seems to have an interest in controlled measurement of such things: I think that you could drastically simplify the complexity (and cost) of these experiments by measuring the water flow at the board and broadcasting those measurements along with a simple time base signal. That broadcast is to be picked up by a laptop computer or other recording device to which you are also recording a video of the ride. Now you have the water flow characteristics quantified and synchronized with a video that shows in great detail what the rider was doing, and to which the rider can add more details about what he did and experienced, in pretty much real time. Saves the trouble and expense of wiring the rider in addition to the board.
-Samiam
RE: Boundary layer effect.
Fast sailboards benefit from fine grit sanding on the hulls and fin surfaces. It helps laminary flow through the boundary layer film. You’ll really notice it at high speeds and on a fast beam reach where you otherwise could get cavitation. Sanding is done excentric on the hull, fore aft on the fin. Fine grit and wet sanding.
Interesting for sure, but I’ve learned to curb my assumptions about what has been written, especially since you can just ask for clarification.
There’s an absolute motion and relative motion here, if you could restate your comments with respect to either, I would appreciate it.
Here, absolute motion is taken to mean with respect to something fixed like the shore, and relative motion is taken to mean with respect to the wave.
And though I’ll wait for your reply, I think it’s important to state that, a change motion requires a force. It’s possible to observe, what might be called an apparent ‘forceless’ change in motion, if the frame from which the motion is being observed is acted upon by a force, that is the actual force is not immediately apparent to the observer. (Kind of like being on a merry-go-round and placing a marble on the floor of the merry-go-round; the marble appears to start moving on its own.) But in the end, if you’ve got a change in motion, a force was required to make it so.
The problem that I have always had is to figure out ‘what makes surfboards go.’ I believe if you know or at least have some notion as to what makes surfboards go, than design elements can be put in perspective. Is it a requirement? Absolutely not - no more than it is a requirement to understand Newtonian mechanics to be a better baseball player, nor for that matter to design a better baseball bat. It just helps.
Many on this forum believe that for the most part gravity makes surfboards go. Gravity plays a big role, especially with respect to certain maneuvers, but I do not believe it is the principal player during the trim maneuver – i.e. the closest thing surfing has to a steady-state condition. Please understand – you could not surf without gravity; heck, ocean waves wouldn’t exist without it (though small, less than 2 mm surface tension ocean waves might.) It’s just that I do not believe it (gravity) is the principal driving force during trim. I believe it’s the flow of water in the waveform that makes surfboards go ,during trim and at other times too.
But here’s the interesting bit; I believe you can design for what you might call gravity centric maneuvers, if that’s what is likely to be important. Or you can design for trim, or obviously, you can design with elements of both in mind – stressing one over the other.
Is this an original thought? No. Journeymen, good journeymen, have been doing this long before I typed a character on this forum. But (and this is the wild stuff) though we might ‘know’ what works and when it does - I don’t believe the ‘why’ is at all clear. In fact I believe the ‘why’ can become pretty detached from reality.
kc
Though you’re not replying to me - your point is taken. This includes your comments about efficacy, which I interpret as suggesting that, thought they (contours) might be doing something, they just may not be doing what they were designed to do.
But back up, as it’s sort of tempting to explore this a bit. There is a big range between glass and say, 6 inch (~15 cm) chop. If you know that you’ll be surfing in choppy conditions is there anything in terms of design that might help? (Aside from doing something else, of course.) What goes into designing boards for Jaws, or Mavericks where chop, and hitting it at high speed seems to be a fact of life? But question need not be restricted to such extremes. What would be the design for head high conditions with a modest chop? Would a little more nose concave help, maybe a little more convex might be the way to go? Or is there something else?
As for the comment about ‘sweet spot’ I also agree. As far as I am concerned this kind of thing happens whenever a design element is taken to far –i.e. tends to dominate. But what does that mean, for surely whether or not a design element dominates will depend on conditions, (which is actually how I’ve interpreted your comments.)
All this tends to make an argument for having a big quiver, which generally isn’t an option for most – that’s assuming the proper board could be selected for the right conditions with the correct level of precision, which at least, I am incapable of. On the other hand, that last comment isn’t an argument for all around generalist board either. Admittedly, I believe surfboard choice is best approached from a more generalist standpoint. Nevertheless bracketing conditions is possible, and hence a smallish quiver does make sense. I guess the point is things change out there, and they do so rapidly, and can do so rapidly on a single wave. Designing for a particular condition and for a particular maneuver should be done with caution. (Which again, is more or less your point.)
In a word, I agree. (I’m just in the mood to go on… it will pass.)
kc
I love this. I completely agree with this notion of uniqueness, and also for ‘reasonable’ tolerance, but I still think a lot can be said for getting a solid notion for what makes a surfboard go (and when.) Understand, I don’t believe there is an ‘equation’, but I do believe there is a set of principles which should dictate and impact design, and in this sense there is a ‘model.’
When I graduated from University I worked for a small aircraft company. The company at the time was designing a new plane (a sort of up-scaled model of one of their successful models.) One of my jobs was to take what the designers (engineers) had and build a simulation. I was completely blow away by the fact that few ,if any of the engineers used any of the kind of math that I was expecting them to. For the most part, if they had a notion of what worked or that some change might help, they had me tweak the model regardless of the physical justification – no equations, it was virtually all tweaks of existing design elements that they knew worked well for some set of conditions -i.e. real experience mattered. But make no mistake, they knew the basic principles governing flight, and if pressed could provide an explanation or something close to it (though occasionally they would say things like, ‘we’re not exactly sure, but it works’, which is not something they cared to say a lot.)
I guess my point is that, I believe we can go a lot further than mere description (which is often taken as explanation.) But I hold little hope for a complete moment to moment understanding of the dynamics – governing principle yes, governing equations, not really, and if so, at best, broad and crude. In the end, this is sort of nice, for like in aircraft design, ‘art and experience’ play very big roles.
kc
I couple of fellows I used to surf with worked for Burton as sales reps. They used to go on about how much money, time and resource Burton was putting into exploring ‘new and different’ designs and materials. I always figured that when some clever business type figured out how to make a killing in the surfboard-manufacturing sector, that we’d see this kind of experimenting and data collection – surely they would be the only ones who would be able to justify the costs involved. Perhaps it might still be the case, but I’m no longer inclined not to hold my breath for any such thing.
Past and present journeymen have taking current design to a remarkable level. Most of the big kinks have been worked out. However, what is not there is a set of relatively universally accepted physically based principles. But that’s ok, especially if you’ve got something that works well enough. From a business point of view it’s especially ok if any further investment in data collection is not likely to improve the product sufficiently to justify the costs. In a phrase – just copy what’s already there - if you want to innovate, change the color. But that’s not all bad news.
The really neat bit about surfboard design is that it has come together as bits and pieces, incrementally, especially over the past, maybe six or seven decades. This is true even when you get those occasional ‘retro’ waves of design elements. We (surfers) are the data sensors, and our clamor has been the metric.
Now if you’re worried about a bottom line, you not likely to innovate –i.e. take risks. So the small builder, or journeyman still owns that aspect of the sport –i.e. for him the risk is in not taking the risk - screw the bottom line. But as you’ve suggested, because of the expense, this innovation is not likely to come about because of hard data collected via pressure sensors and such.
kc
PS
Even so, dido with respect to winning the lottery - it would be geek heaven for me.
I think you right.
But its all about money, which I assume isn’t there. But you’re idea is on the ‘money’ - we have the technology. The telemetry aspect is neat.
kc
If you can count on a ‘flow’ you can model for it, but in surfing you can’t count on a given flow. Well, at least that’s my opinion.
It’s tempting to visualize the flow under a board as almost completely nose-to-tail, but I don’t believe it even comes close to it under most circumstances. Don’t get me wrong, during certain maneuvers, it surely does, but most of the time it’s at best what you could call rail-to-rail, or center-to-rail, etc. and even then its likely to change a lot.
Though surfaces like sandpaper tend to be unidirectional, they work best once a flow establishes itself, which doesn’t happen that rapidly. That is, all the transient effects have to settle down before the full benefit of the surface can occur. If things are changing fast, surface textures other than ‘as smooth as possible’ can be a detrimental. Of course, I actually don’t know for sure if the establishment time of a given flow is truly a factor, but my guess is that it would be. My evidence for this is ‘Nature’
Compare surface textures of the skins of marine creatures that tend to change direction and move around sporadically, with those that tend to make longer pursuits. Its not an exact correlation but there appears to be a trend – smooth works better for a lot of stop and go, rough, on the other hand may work for continuous relatively unidirectional fast motion. Of course the complete environment and behavior of the creature should be factored in.
The occasional comment about sharkskin has been made in this forum. I’d love to hear the arguments, other than ‘it works for sharks.’ My argument would tend to be that, it does work for sharks but not always. It works for them during those long patroling stretches and not necessarily when they are in the throws of an attack (at least with respect to flow, though having nasty skin surely works against the prey.) Nature has made the calculation, and has come up with the balanced design.
But opinions differ. I’d love to read more.
kc
Lots of talk about speed, drag, and measuring flow under surfboards as a design tool.
How about starting with an aspect of surfboard function which is easily measured. . . . . surfboard speed ?
Though you’re not replying to me - your point is taken. This includes your comments about efficacy, which I interpret as suggesting that, thought they (contours) might be doing something, they just may not be doing what they were designed to do.
But back up, as it’s sort of tempting to explore this a bit. There is a big range between glass and say, 6 inch (~15 cm) chop. If you know that you’ll be surfing in choppy conditions is there anything in terms of design that might help? (Aside from doing something else, of course.) What goes into designing boards for Jaws, or Mavericks where chop, and hitting it at high speed seems to be a fact of life? But question need not be restricted to such extremes. What would be the design for head high conditions with a modest chop? Would a little more nose concave help, maybe a little more convex might be the way to go? Or is there something else?
As for the comment about ‘sweet spot’ I also agree. As far as I am concerned this kind of thing happens whenever a design element is taken to far –i.e. tends to dominate. But what does that mean, for surely whether or not a design element dominates will depend on conditions, (which is actually how I’ve interpreted your comments.)
sorry, i intended to reply to you. I also wanted to mention that i was not refering to bumpy/crappy conditions but rather slight bumps and ripples as caused by offshores. as an example i had a six channel bottom shaped by hamish graham, regarded to be a master of channels, for a g land trip a some years back. g-land of course is a fast down the line type of wave on which channel bottoms are said to really excel. i found the channels to have some efficancy in the morning glass. when the typical g land offshores would pick up, which generally arent howling winds, that slight offshore ripple up the wave faces seemed to negate the channel bottom benefit. i would have to say the same to concaves ive had at g land on subsequent trips. its been my observation that when any air gets under concaves or channels the efficacy seems lost. i would theorize that the air disrupts the flow. having said that i think phazer bottoms might deserve more attention but i would guess their benefit is even more difficult to feel or quantify than concaves. fun talking about it all anyhow!
-you’re absolutely right that all of this points at having a huge quiver!
Sounds reasonable to me.
I’ll start, speed is not as important as the ability to accelerate and decelerate. I believe this because; most of the time ultimate speed requirements are dictated by the wave, or conditions.
Consider, some guy walks into a surf shop and seems to be interested in some board. As he’s standing there ogling the board the shop owner comes over and says ‘that’s one fast board.’ This actually happened to me a while ago. My reply was ‘What’s that mean?’ His reply was, actually I’ve forgotten his reply. But my point is what does it mean to say a board is fast? Are other boards therefore slower? If a board meets the demands placed on it, isn’t that fast enough? And by meeting the demands placed on it I mean ‘track the wave the way you want it to’ - whether fast or slow -i.e. accelerate and decelerate well. I’m hesitant to throw new language into the mix, but ‘holds the wave well’ is something I seem to want to say.
(((ding)))…My time is up, your turn Roy.
kc
Have you taken a bonzer out at g-land? If so, would you describe the bonzer you rode (was it a full Eaton bonzer with all the humps and bumps, or some other variation) and how did it feel?
Forgive me. I don’t get out much - pretty much a local boy who stays put, but I’m interested. I’ve always been fascinated by bonzers, especially Eaton’s.
kc
Hi Kevin,
Top speed and acceleration go hand in hand. . . what leads to one leads to the other.
I’m suggesting speed measuring because there seems to be a desire to record meaningful surfboard performance data. … . . and speed data , although it doesn’t tell us everything by any means, is useful and interesting design feedback which we can get in the here and now without any new technology. . . so it’s a good place to start IMO. . . (and fun for competitive types who like to brag ! 
)
no…shame!! ive never even riden a bonzer!!!
this aussie guy named ‘Camel’ has some strange live/work arrangement at g land and has been there like 15 or 20 seasons. i think he used to surf at the semi pro level in oz in his younger days. anyway the guy is real experimental with boards. hes got an older pushed forward center point single fin with the fin set at angle for lefts…as g land is. anyhow, he’s probably riden a bonzer there and would have good feedback on probably every other design known to man if you could ever find him!
Have you taken a bonzer out at g-land? If so, would you describe the bonzer you rode (was it a full Eaton bonzer with all the humps and bumps, or some other variation) and how did it feel?
Forgive me. I don’t get out much - pretty much a local boy who stays put, but I’m interested. I’ve always been fascinated by bonzers, especially Eaton’s.
kc