Good idea wildy. I found one on sparkfun’s site. It has an accelerometer, gyroscope, and magnetometer. This in combination with a GPS unit would provide a lot of information. The video I posted above is a demo. Would be pretty cool to go back in time, and put one of these on some of the boards from epic rides of the century to recreate them.
Although I am not sure to what end this would serve. I do equations all day long… I like surfing because in some regards, precise equations have no meaning in this context. I don’t advocate putting fins perpendicular to the stringer, but the best method is to try to different ideas. Come up with a fin design then surf it. Does it feel good? Do you surf better? Adjust it just a little. In other scientific endeavors, it is clear what function to optimize. In this situation what do we optimize? I think this is best served as design evolution, i.e., try a bunch of random designs, and whatever works well stays around. To learn what works, we ask Bill:)
In extreme conditions, like 20ft Makaha, simulations would help. For instance MIT has some fluid tanks, so it would be possible to put fins and observe the effect on moving water. Maybe this would give a better idea on coating, and shape.
This link is pretty neat. It has some quick snippets of the research they do. They even look at extracting energy from waves using hydrofoils.
http://web.mit.edu/towtank/www/research.html
Also bullshit on proving any of this mathematically. I believe that would be a Millenium Clay Prize.
http://www.claymath.org/millenium-problems/navier–stokes-equation
On another note, in some regards Newtonian Physics is an “opinion”, or maybe better put an approximation to reality. In particular if all we had was Newtonian Physics, we would not have GPS. GPS is dependent on special and general relativity. Clocks run at different speeds up there and down here…
Relativity is certainly involved. Groundspeed vs. airspeed.
Has Relativity been fully substantiated? Grand Unification?
What happens to mass at the speed of light?
While there are a large number of variables, I do not think surfboard performance has pushed the envelope of physics just yet…
Having been challenged to put my money where my mouth is here’s a very basic explanation of stall flutter and how it might be reduced by increasing fin area. (Sorry it’s taken a while I’ve been busy.)
Okay diag.1 is basic enough and shouldn’t need any explanation, nor shoud diag. 2.
Diag. 3 shows a fin approaching stall as can be seen the lower surface should still be relatively lamina while the top surface is displaying turbulent and chaotic flow; this happens from about 16 degrees AoA upwards. This is where several things happen simultaneously
The board is in trim – i.e. not turning.
As the wave becomes steeper the board provides proportionally less vertical force compared to the fin.
Therefor the fin is required to provide more vertical force in order for the rider to maintain a constant position between trough and crest.
All forces increase with a function of speed squared.
Lift increases linearly with AoA
Drag increases exponentially with AoA
……until the stall angle is reached
When lift decreases but drag increases even more.
So, in order to maintain a steady line that requires increasing lift transferred from board to fin to cope with a steeper wave speed and/or AoA need to increase accordingly – this pushes the fin closer to stall.
Now, on a raked foil in particular the pressure redistribution will create an external moment twisting the fin to align with the flow. This will lead to pressure recovery.
Due to the elastic (flex) properties of the foil it’s now possible for a dynamic oscillation to occur – this is known as flutter.
Aerodynamic flutter is overcome by slowing down as this reduces the pressures allowing the oscillation to stabilise.
In a surfboard the easiest way to avoid flutter would be to fit a higher area fin thereby reducing the AoA needed.
A stiffer fin would have a higher frequency oscillation.
https://swaylocks7stage.s3.us-east-2.amazonaws.com/s3fs-public/Flutter.jpg
You are just being silly now:)
1)Relativity is involved because the satellites sending out the timing signals are a)further from a large mass , earth , and therefore the clocks run at a different speed.
b)the satellites are moving very fast with regards to anything in earth’s atmosphere , once again the clocks run at a different speed.
Two different effects.
This is undergraduate physics. My point wasn’t that there are relativistic effects that need to be taken into account for modeling surfing, My point was that gps has to take them into account, so you can watch the video of Slater with his speed displayed.
In addition , gps works, simple explanation, by sending out signals from satellites and using the time difference between signals received at the location of interest from different satellites, to come up with potential locations. A system of equations is solved that results in you position. GPS does not measure speed, although velocity and acceleration can be derived from subsequent position samples.
- Relativity once again is theory and approximation to reality. Mostly everything we have are only approximations to reality.
3)Seriously? What is the speed of an unladen swallow?
4)I made no comment that surfing has pushed any limits of physics. I made a simple comment that there are too many variables to effectively model any solution without testing it in the water.
I apologize if I come off as rude, but it is annoying to read all the posts referencing centripetal accelaration and the one formula you always post. That is nice, but try and plug some numbers in, do something with it
Me again,
Nice explanation. Once again not a proof, but a culmination of knowledge derived through experiments. Sort of like any surfer that may not be educated in hydrodynamics, but has been surfing for a long time and knows what works and doesn’t works.
Although your explanation does give a better understanding of what is happening, Thanks it was illuminating.
hopefully we can come up with a good way to measure some of the effects fins have on speed and control.
My take on this thread is that it could have been of great value, but it’s become a waste of time. I wish people would show actual fins that work and explain why and when they work best. A very interesting topic would be the assymetrical foils a lot of guys are using and the outlines that are very different from the norm. Another is how the placement, cant and tow can make a big difference.
Responding to Melikefish:
I will continue to post centripetal acceleration as often as I hear how turns create speed and drive. Or as ofen as I see comments that surfers do not generate enough force to flex a board. Or as often as I see acceleration equated with an increase in speed.
I have plugged in values. I repeat these few numbers from memory so they may be a little off:
A force of 3G will be experienced:
21 mph with radius 10 feet
18 mph with radius 7.5 feet
15 mph with radius 5 feet
I have seen my limit (quota?) of mysticism and religion in place of “basic science.” I have seen more than a few threads claiming incorrect/unrelated science as the mechanism of performance. I am as tolerant as those who are posting.
How does an affordable accelerometer detect the difference between centripetal force and gravitational force – especially without recording concomittant speed values? It is my understanding that GPS devices are not particularly accurate in detecting changes in vertical position relative to the ground – especially changes of a few feet. How is the efect of a fin being differentiated from the effect of a rail?
I am sure I have many typos as I am typing on an I-pad.
EDIT: I posted a response about the airspeed velocity of an unladen swallow – African & European – a while back in a thread started by Everysurfer…
Standard foils are readily available check Theory of Wing Sections; Abbot and Von Doenhoff - 1946 (Yes first published in 1946!)
To generalise;
Flat sided fins are close to a Clark Y (1922) and while pretty agricultural will do a reasnoable job.
If you want a good fin section I’d suggested a 64xxxx (perhaps an A) this has a distinctive drag bucket but still reaches a reasonable stall angle without losing too much.
Thin fins produce less drag at zero lift and low AoA but stall early
Thick fins produce more drag at zero lift and low AoA but have better stall properties (i.e. stall later and with less drag at high AoA)
Rake improves stall properties, increases drag, and induces torsional moments that will induce load alleviation
High aspect ratio fins improve drag properties but reduce stall properties
Unusual fins might be great for 1% of the time but will generally be worse 99% of the time (mini leading fins for example)
As long as the leading edge is rounded and the trailing edge is sharp and there is a smooth transition from one to the other you won’t go far wrong.
Lift and drag are something of a misnomer in surfboards - I personally think it would be better to think in terms of pressure distribution and only if absolutely necessary resolve this to vertical, cross wave, and shorewards vectors.
stop being a knob Stoneburn…(lol)
Tell me about it Kayu…
After all, you are the pro.
I usually gain new insights from the solid scientific discussions in threads like these. Is learning about the science of performance that offensive to you?
No…just get a bit tired of you taking known facts about performance , and turning them into “War and Peace” sized posts that drag good topics into La-La Land…(lol)…do you write a 10 page thesis on the physics of can-openers before you open the tin ?
Apparently not all of us are as enlightened as you.
Fortunately Kayu, we have you for solid, on-topic and stimulating contributions.
A wise old owl (Oneula) mentioned on another thread it is the point to match the shape to the type of wave/break. INDEED. This concept made me start shaping. I needed a shape to work with my big ass and types of breaks at home…a neverending pursuit.
I found that both flex and stiff fins work in the proper conditions almost diametric from each other.
I was lucky enough to score Laniakea at it’s best, speed for days. That go out showed the merits of a stiff fin.
At home on the mainland, most breaks for me, require flex because I want to turn from the center of my board. This concept was proven to me at Greenough’s own stompimg grounds…The Ranch. Cojo’s told me to run the flex. It works there.
Wouldn’t consider arguing with Mr Thrailkill. Either the “kool aid” worked on me or there are times flex is cool.
Quite so. A little snippet of fact is that in many fluid dynamic situations drag at an AoA below 4 to 6 degrees is very very low - Google “drag bucket”. (Lift Coeff is pretty much linear till 16 degrees ish). What this means is that if you can keep the angle of incidence between board and flow direction below 6 degrees you get very little drag. The trick of course is matching the bottom shape of the board to either a specific or generalised shape of wave - and that is where the science and the emperical experience combine.
Hope this helps.
The Kool Aid worked.
Pressure distributions are lift.
The problem most people have with thinking about the science of surfboards is 1) they don’t understand how the water is moving in the wave, 2) they don’t realize the variarion of flow and the various lift/drag vectors (which are happening, simultaniously, across the board in different directions and magnitudes).
No they are not.
They act in different directions and don’t even have the same units.
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The Kool Aid worked.
It sure did…Hah! Through the purple haze, it is sweet.
For waves with little juice, I still dig a little flex.
Juice is hard to find on the mainland.
Pure Hawaiian Juice…nuttin’ like it.
…
I like the idea of plotting accelerometer measurements over the track and time of a ride.
But for studying the “speed” effects of any given fin design, it seems like overlaying data collected from a “flow sensor” with the video of a ride track might be particularly instructive.