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@Horton‌ , very cool. Any idea what the sampling rate is?

Now for some real fun... I'm hesitant to post these for fear of creating more confusion than clarity, however since there seems to be interest I'll proceed at risk. Please keep in mind as you look through the charts below that the 1 g of gravity is still playing a role in the data. Below are the individual charts for each of the x, y, and z components of acceleration in g's, relative to the accelerometers coordinate system, of the total acceleration graphs previously posted. For reference, I had it taped to my sternum such that positive x was up, positive y was to my right, and positive z was straight ahead. And now for the really cool part... a quick and crude integration of the y-acceleration into y-velocity (again y being left and right). As you can see the data has an artificial drift, I suspect this is the bit of the 1 g of gravity playing a role, or possibly a stacking of error in my crude integration method. But... the information is in there... just need to clean it up.

@Waternut‌ , I agree, it would be great to compare side by side with video. The sensor I'm using uses a real time clock for the time stamps, so it would be feasible to match it up assuming you calibrate the clocks between the video camera and the accelerometer... and had the time to actually go do it. Unfortunately I don't see myself getting around to that anytime soon.

@Than_Bogan‌ , I'll answer the easy ones. I'm having a hard time pulling myself away from the analysis to respond, only so much time in the day. I could argue for or against whether or not to include the 1 g of gravity in the total g's one feels; a counter argument would go something like... if the accelerometer were in free fall it would record 0 g's, if a person were in free fall they have a sensation of 0 g's, therefore an accelerometer reading of 1 g would equate to a sensation of 1 g. Either way, I did not actively leave gravity in the data, I quite simply hadn't yet figured out how to remove it. Removing gravity from a moving coordinate system is a bit of a puzzle. That being said, I like your concept of just removing it from the vector sum with a floor of zero. I don't think it provides much more insight into the progression of the analysis since it does not help remove it from the individual components (x,y,z), however it is interesting. To your second question... the charts are in fact g's, not g^2. The sensor records in units of g's, if you set it on a table it would read x = 0, y = 0, z = -1. The first graph (from my previous post) is simply the absolute value of the vector sum, f(x,y,z) = sqrt(x^2+y^2+z^2). The graph in this post is f(x,y,z) = sqrt((x^2+y^2+z^2)-1) with a simple 'if' statement to floor it at zero.

I neglected to label my chart axes, Y is total g's, X is the time stamp in seconds.

I read a fair amount of this forum but almost never get around to contributing. However, the timing of this subject was just too perfect and I haven't seen anyone post any actual data yet (if something has already been posted in another thread I missed it). I've been playing around with an accelerometer for a bit and just took some readings this last weekend. A few points of interest on the data: it is a 3-axis accelerometer, the measurements include 1 g from gravity, I recorded at 800 Hz, the time stamp precision was set to 0.1 milliseconds. I recorded several ski sets but did not take notes on which set was which and I tend to jump around a lot with speed and line length, so the data was either 34 or 36 mph and either -22 or -28, but it was a full pass. (I'm a -28@36 skier on a good day, a couple at -32 on a really good day) If I spent the time I could probably figure out the speed based on the time stamp, but right now I'm just playing around with what I can do with the data, not spending too much time on what the data is actually saying... I'll leave that to the forum for now. The chart below is with the accelerometer "rigidly" duct taped to my sternum (center-of-mass'ish). The chart is a combination of the three axis vectors summed into a net "g-force" magnitude: g^2 = x^2 + y^2 + z^2. My first impression... the data is way more dynamic than I was expecting. Peak g's appear to be just shy of 4.5. My plan was to integrate the acceleration into velocity to add to the info, but this is proving not to be as straight forward as I first anticipated. For the moment I'm simply in data overload. And yes, there is a significant amount of error as you integrate acceleration with known error into velocity, and more error stacked on integrating from velocity to position. So, the velocity numbers may be questionable, but I think they may still prove to be interesting. GPS contributed data would be great, but for now all I'm working with is an accelerometer.

It amazes me that the snow ski industry, for the most part, seems to have uniformly settled on a particular binding release system and water skiing seems to keep fumbling around trying to figure out which way to go. It’s even crazier considering that the snow ski industry has already done a good chuck of the work by defining “reasonably safe” criteria for maximum heel lift loads and torsion loads and offered it free to the world. All I can figure is it’s simply the nature of being a much smaller industry therefore far less R&D money to go around and therefore much slower to progress. Rubber bindings were great for their day but they really have outlived their evolutionary life span. One of the biggest issues I have with rubber bindings, and the newer hybrid styles, is that they are slow to release. Bones don’t break slowly, when ultimate failure load is reached they break, nice and simple. Bindings should function in the same fashion, only with the release load set reasonably under injury loads. I commend Goode for pushing innovation with the dual-lock system, but I’d say it was questionable at best from a “safe” point of view from day one; far too much variability in the materials, the setup, and the end user setting it up. Dual-lock could be a great improvement over rubber (from a safety point of view), but it’s hard to say without any unbiased data, e.g. number of injuries per year per style of release system. In my opinion the Reflex system with the Silvretta release, and the few other similar systems out on the market, are far and above the others in regards to safety. The Silvretta release taken straight from the snow ski industry, coincidence… And there’s nothing stopping you from taking your Reflex setup to a snow ski shop and having them perform a heel lift check and comparing it to a DIN chart if you have any concerns on your setting. In regards to a single pate vs two separate plates, I once thought it always better to have either both feet in or both feet out. Recently I’ve reconsidered this after giving it some deeper thought inspired by watching a few injuries. A single release plate for both feet (as used in a dual hard shell with dual-lock setup) seems quite foolish. Your right leg couldn’t care less what loads your left leg is seeing, it only cares what loads are on it. Each foot needs the ability to release independently. On another note, why have no major binding systems captured a torsion load release case? It would save a lot of knees, and a few ankles, bones, and hips. Here’s a random suggestion: request USA Water Ski to mandate the recording of equipment make/model/year for every serious injury that occurs at a sanctioned event. They could then compile that information and release an objective listing of number and type of injuries per each brand/make of binding. Without unbiased data it’s very easy for the masses to be swayed by good marketing and hype. P.S. no returns on those Strada’s I sold you a few months back, you know who you are…

I've been reading your forum for a bit, finally decided to chime in on something... I don't know too much about how thickness effects the hydrodynamics (so I found your comments rather intriguing), but I can share some thoughts on how it effects structure. I might be stating the obvious here, but thickness has a direct effect on the stiffness of a ski. Ski construction is typically a basic cored panel: fiber reinforced composite top skin - core material - fiber reinforced composite bottom skin. This panel forms an "I-Beam" structure. As the ski is flexed the top skin goes into compression, the bottom skin goes into tension, and the core goes into shear with the neutral axis somewhere near the middle. To simplify beam theory... stiffness is a cubed function of beam thickness. So a little bit of thickness, either added or removed, has a rather large impact on stiffness. Not to mention removing unnecessary material sheds weight. I assume this is why there's quite a few slalom skis out there with very thin tips, trying to shed weight up where stiffness is not as important. Or maybe it's just good marketing... ~tap