The Definition of Speed

[Horton]

I am working on the darn N1 review and wrote the below. Any one have any thoughts? (it is a first draft so spare me about any typos)

 

The two definitions of a fast ski are “a ski that achieves width with less than optimal rope tension from the second wake out” or “a ski that requires less physical strength and effort to get from side to side”. Generally speaking fast skis tend to be finicky at the apex of the turn and are less stable approaching the ball. It is assumed that a faster ski literally ride higher in the water.

 

Slower skis are often described as having a more stable and tactile feel approaching the ball. Especially at 34mph slower skis require better management of rope tension to achieve width and more strengths to get from side to side.

 

[thager]

I thought speed equals distance divided by time? In a nutshell, a fast ski covers the course width quickly but usually takes extra time and space to turn. These skis usually ride higher in the water and skid turn a wider arch. Bevels are usually smaller, sharper and ski flex firmer. A slow ski covers course width in a slightly slower time segment but the turn is carved smaller and quicker. This ski usually rides lower in the water with more drag and has larger rounder bevel combinations and/ or a softer flex. The challenge is to combine the best charectoristics of both. What you have is a ski with the right combinations of bevels surface area , materials and flex.

[Horton]

@thager Hmmm I 65% agree

[A_B]

Faster skis to me seem to have more "bite" or edge holding power, that requires less effort on the skier to maintain edge and direction. The skier's observation of being early causes the percetion of being fast cross course, when in reality, it actually might be a "stickier" or slower ski, as far as surface friction etc.. Does this make any sense?

 

I know when I am late going into a buoy, they all seem fast.

[thager]

@Horton 65% on a very good day is pretty much what I can remember of anything! I am obviously guessing.

@AB A fast ski to me is one that jitterbugs across the surface barely staying in contact with the water. A slow ski feels like it is suctioning inself into the water dragging along. An equal pull initiated at the same time from the same point would put me in two different places. Unless of course I go straight at the ball like I do then both feel fast! Perception is a big part of this. Really hard to measure unless skiing on each alternately.

 

[A_B]

@thager, I agree. Most of the times I hear my friends try a ski they say it's fast if they get there with more distance in front of the buoy, or if they are scrambling they can get back into it. I am not totally sure it has anytning to do with speed opposed to easily rolling onto and staying on edge when needed. Maybe the real effect is not coming off edge as soon and then you are getting a smidge more speed later into the ball?

My BDawg friend was on a Mid for a couple weeks when they came out, and it appeard feom the boat to be very fast cross course but he could not hold initial edge out of the buoy with it, in particular his onside turn. We were theorizing that his RTP was not helping drive it around the turn as it may have been riding higher on the water, but once on edge it took off quickly. He didn't keep it, but thought it was the fastest ski he had ridden in a long time.

[ForrestGump]

I equate speed to effort going cross course. An X7 takes more effort than a Razor, let's say. To me the razor is faster.

[6balls]

My first set on the Razor it almost dumped me from 1 to 2 because it shot out in front of me. I got used to it quickly, but was just unprepared for the burst of speed. Very fast ski that also really turns. Had the season of my life on it.

I do think D3's hit the magic spot for many as a forgiving ski but one that still has a serious short-line envelope. I skied 'em for years and really liked them.

 

[jayski]

"Speed is merely a perception"...not a realistic word to use for descriptive purposes of a ski...unless mathematical evidence is present to provide factual results the description is unfounded and misleading...(quote from one of the most technical coach/skier)

[A_B]

Skiing is not a science, it is part art and part physics, but the art part of it is what is felt and differentiates skiers. I would guess a concensus of the artists would say that less effort with similar results equates to speed. There will be naysayers that say you need a radar gun to prove.

 

Take the extreme of jumping and what ski design has done to increase speed. If slaloming the course was about fast skis, we would all be riding GoodMANs not Goodes.

[Brady]

@AB ...all be riding GoodMANs not Radars. :)

 

[Bruce_Butterfield]

Speed by itself can be a very misleading description. We humans frequently relate "fast" to "out of control". Hence a very out of control ski can be perceived as fast even if it is going very slow. Conversely, a very stable ski can be perceived as slow, even if it is in fact very fast.

 

So the trick is to separate the perception of speed with the actual speed. Since this will be different for almost every skier, I think describing any ski as "fast" or "slow" should be avoided.

 

Its much better to stick with descriptions like

"....effortless to ride...",

"....carries width to the buoy...."

"....had to work my ass off to get any width..."

"...felt like a skateboard on ice...."

 

I think your initial descriptions of "ski that achieves width with less than optimal rope tension from the second wake out” or “a ski that requires less physical strength and effort to get from side to side” are much more meaningful than trying to put it in terms of speed.

[A_B]

@douglaslbrady, it just didn't seem as poetic.. I have been skiing on 2 Radars this past year, and no Bruce, not at the same time...

[Razorskier1]

I think of it as the ease with which the ski runs cross course. With my Razor I feel like if I just stay quiet over the bindings the ski will run with great angle and generate great width. I skied a softer flex ski for a couple sets this summer (Razor B flex) and it felt sticky, like I couldn't make it go without really getting on it.

[Horton]

Well looks like I will have to include my definition in the review and expand on it - it is not the same as everyone else thinks. Hmmm

[The_MS]

Fast ski (speed) = consistently waiting for the next ball while in control. A ski will always feel fast if this happens.

 

[Than_Bogan]

Don't forget, it's only because of the air that you have ANY sensation that is related to speed itself. Acceleration is the thing you can feel.

 

So when we say a ski is "fast" we're not taking about distance = rate*time at all. We're talking about some sensation that we have, and I don't think I can do any better at nailing down where that sensation comes from than has already been done above. Bruce did the best in my opinion.

[Than_Bogan]

Minor note: Radar guns are not accurate for measuring things that aren't travelling with a constant velocity vector and in a known-in-advance direction. Skier fails those criteria badly.

[Than_Bogan]

Fwiw, here's the main way I tried to tackle this "speed" issue in my N1 review:

 

The weird part of this is that it damps that cycle of acceleration and deceleration that is the roller coaster ride of a slalom run. So that’s how the ski can seem “less fun.” Staying on a better line with a closer-to-constant speed is great for running more buoys, but it’s a little bit less of an adrenaline rush. Instead, that rush now comes on the way out the exit gate at -38.

 

In addition, I believe this is the main reason that the ski feels “slow” in one interpretation of that word. The actual speed of the ski is excellent, proven by arriving early at the next buoy. But thanks to Newton’s laws we can’t feel speed – only acceleration. Thus the whole experience on this ski doesn’t feel as “fast.” In the end, I’m pretty sure that’s a good thing.

[Horton]

@Than_Bogan

Lucky for both of us there is no right or wrong but I disagree with that part of your review. Trying to get mine done.

[danbirch]

Good Speed = Cross Course Speed. Bad Speed = Down Course speed.

If you have a fast ski, it means you get cross course quickly (i.e. white water to white water), and therefore are early into the ball, and it actually feels SLOW & CONTROLLED.

 

If you have a slow ski, you travel cross course slow (i.e. with more down course speed, less cross course speed), get late into the ball, and feel FAST.

[estrom]

**Assuming the same turn with good technique leading to a stacked position....

 

A fast ski gets your heart pumping and adrenaline flowing as you think, "Holy crap I'm flying!" A good ski will allow this while remaining in control.

 

A slow ski will have you thinking, "Where's the whip?? I feel like I'm riding a mule plowing corn."

 

That's a not-so-technical look at it.

 

[BraceMaker]

So we need an inline load sensor and an angle sensor on the rope. This would generate data over time.

 

The data would give change in angular position which graphically would provide both velocity as well as acceleration. Compared to line load I think you would have a decent measure of ski speed. Of course you would have to normalize data. Perhaps view gate and 1 ball as a certain data set. View 2-5 ball as real data. And ignore sets tht arent full passes.

 

Fast ski should show reduced line load for the same change in angular position or more angular position at less load.

 

Fun stuff. Anyone do load cell programming? Note angular position can be graphically sourced.

[Than_Bogan]

Very cool idea on measuring angle of rope. But if you do that near the pylon, which is the only way I can think of, then the slightest bit of slack can give you crazy measurements.

 

Still, I'm intrigued. Never heard that before, and since you know the rope length and can infer boat position simply by time, that's enough info to compute the handle path. If the rope is straight...

[BraceMaker]

Right Than_Bogan - but for the purposes of the "speed" of a ski, we don't really care about slack at the ball, or lose line going into the ball, we can infer that since the skier "made the pass" that once the crazy data smoothes out, the skier has "hooked up" and the ski is on acceleration. Hence with a relatively small amount of data (rope tension and angle) most of the parameters from the hook up to the turn are pretty well known, as you mention, with rope length, you basically know the linear distance travelled, the math there seems pretty basic.

 

If you wanted to "smooth" the data after collection by using software to blend peaks and read averages over time you could. Also this is all data that can be collected "behind the scenes" you can equip a tow boat and really not have the skier be aware.

 

Next point, this data could be predictive, that being for a skier you could possibly predict how they would do with enough data for instance if @ 38 off a skier is accelerating at x m/s^2 and they usually run 3 @ 39' off on days with similar data, you could actually create a decent training package.

 

 

This is all stuff I've been thinking about today... so it is very well thought out...

[jipster43]

To suffer the penalty of too much haste, which is too little speed. - Plato

 

[jayski]

@Than_Bogan @BraceMaker

I do not possess the technical knowledge that the two of you seem to possess, it why couldn't you set up some type of measuring device on the ski? Like a paddle wheel type unit or, mini pitot tube? Maybe set up off the tail of the ski?

 

I think what the two of you are looking towards is long overdue, we are in the stone ages when it comes to data collection to increase skier performance and ski design...keep it up!!!

[BraceMaker]

@jayski - measuring the ski is more tricky, weight/drag/lift etc. all come into play, plus you must implement that on every ski, and on every run. And if you are worried about good data - you'll lose that data rapidly when the ski goes through turbulence, chop/wake, goes airborne, or the sensor is up in the water.

 

I believe you can get good CLEAN and USABLE data off the pylon. As I referenced, we want load and angle, and since the load occurs @ the same angle as the line, we can technically just have a pylon with load cells or physical measurements, for instance pylon deflection can be "mapped" we could use 3 digital micrometers mounted around the pylon, most likely using 0 degrees as the bow, 180 as the stern, have one at 0 degrees, one at 120 degrees, and one at 240 degrees. Hence when a skier pulls out for the gate, the pylon pulls towards the 240 degree sensor, when the skier is straight behind the boat the 0 degree sensor reads distance increasing, the 120 and 240 sensor read the pylon as closer.

 

This is just one idea, but simply this 3 measurement system would tell you where the skier was and how much force. From there we just calibrate the system using a scale and a 1 ton ratchet strap, we then could set up the force curves for deflection and angle.

 

Idea 2 is simply an inline variable load switch (just like a jump switch, with variable resistance or voltage or what not). Then we utilize either A- video analysis to do angle, or an idea similar to "the tracker" type system with a U for the rope that reads angle and outputs it.

 

Frankly if you want this data it is fast and simple to acquire, highschool physics does accelerometers.

 

Its how you use that data - so if you have a way that the data goes into a system where you can use it to compare varied states - ski vs. ski, skier vs. skier - fin deep versus shallow, bindings forwards versus back.

 

Powerful tool.

[Than_Bogan]

@BraceMaker That's another great point: There are very important regions, worth measuring, where the rope is assured to be tight.

 

It's probably a silly overkill, but as someone who does machine vision software for a living, I can say it should be quite doable to measure the rope angle in a fully automated manner from an overhead video. In fact, such a system could also be made to detect when the rope was slack (with some degree of correctness, anyhow).

 

BraceMaker Where are you? I don't how the hell I would make time to work on this seriously, but it's worth giving it a little consideration if we could collaborate to do something really cool. Feel free to respond by private message or right here.

 

In the past, I've done a buttload of math to try to make some guesses about many aspects of slalom path, but ultimately: a) That math gets damn hard damn fast (I've involved some hardcore mathematicians and still been stumped on some things we wanted to do) and b) Math is really limited without the ability to measure stuff (and raw measurements are very hard to interpret usefully without math...)

 

The fundamental thing that always stops me from going further is: What would we REALLY learn from all this effort?? Would anybody actually run more buoys?

[ForrestGump]

Damn math geeks think too damn much. :)

[Than_Bogan]

An old friend of my dad's was known for certain obvious-yet-profound statements that became known as Reynold's Axioms. One of these was:

 

People will do those things that they can do.

 

How this applies to my skiing: When thinking is all you've got, that's what you have to do. I'd be happy to use athletic ability instead. Got any I can have? :)

[BraceMaker]

@Than_Bogan - What we'd do with the data....

 

Well, essentially I think the biggest value would be in training. For instance days that you feel "slow/late/narrow" you can go back to the data and determine if your pull is coming on late (remember this would show as the load being at less angle) or you could determine if you are not pulling as hard (low load) or if you are pulling long - would be interesting to see the line load from the supposed early edge change.

 

I think from a coaching perspective, you could easily show a student graphically variations between sides, variation between passes, pulling too long, or too short, or not through the wakes.

 

I suppose it could also be useful to take line load from one side of the boat and view that as "positive" and the otherside as "negative, hence your graph would be a wave form around an axis, and you could mirror the data and view variation.

 

Dunno, I am not:

A: - Programmer

B: - Mathmatician

C: - Electronics Guru.

 

So I'm viewing this more as a thought process, but would like to talk more Than... SO I will Pm once I get my evening sorted.

[BRY]

I think @Bruce_Butterfield nailed it (again).

Everyone is trying to attach additional attributes to "speed", to give "speed" deeper meaning. Effort, feel, hold, are attributes than need to be distinct and anylized in of themselves, not as component of "speed". All speed is:

 

Distance travelled per unit time. Speed is the scalar quantity that is the magnitude of the velocity vector.

 

The confusion and difficulty comes from trying to redifine the term. I suggest using Butterfield's advice.

[thager]

Thought I said that?

[BRY]

You did, but... a couple screens of definition and interesting ideas on measurement thought I would put my opinion out there. A vote sort of for Horton on how to proceed based on his original question. I'll be quiet now.

[jayski]

Data collection is/would not be just about speed, it's about all apsects to maximize performance of the skier and the skis...It does amaze me that there isn't pros riding proto skis with sensors all over it collecting data, along with ones on themselves to track movements, muscle use, etc...I realize that funding is a large part (and not necasssarily available) of this but truly believe the skis could be vastly improved and the athletes themselves.

[DW]

There are several data aquisition systems on the market that might/should work to gather the necessary data to in the end, be able to plot X-Y plots of path, distance, speed, acceleration. I don't think the sample rate would be challenging, much slower than the 1000Hz required for shocks as an example. The keys are mounting on the ski, waterproofing, the roll effect of the ski itself and maybe the synching with the entry to a course.

[thager]

@Bry No need to be quiet. Keep it coming! Didn't mean for it to sound the way you took it.

[BraceMaker]

@Bry - quiet on the set! screws up your wake.

 

@DW - I guess to me many of the parameters are not critical - we know the ski will have roll angle, but that will depend on the skier, the bindings etc. And we know that since most people ski somewhat different, and utilize different set up/fin/binding location, lots of that will vary. And are a whole nother set of data- could be intriguing data.

 

But for the question of "speed" I would care most about successful course runs on a ski, and how much work the skier does. Fastest way to "work" is to measure the force and then the motion that the force creates (word - force(distance) distance is a factor of simple trig based on line length and change in angle. Hence the equations allow us to extrapolate the data based on measurements taken boat side, with fewer issues of weight/power/waterproofing/mounting.

 

The other sets of data I think would be intriguing, particularly for a ski designer... or a biomechanist.

[DanE]

To just determine top speed for a ski /skier Do we really need to measure load?

Wouldn 't it be enough to measure angle rate off the pylon, put in Boat speed and Line lenght Into the equation and then let the math guys Do what the Do?

[Than_Bogan]

@DanE Yes. But there are other things interesting to know.

[Than_Bogan]

Also, keep in mind this scheme computes handle speed. At times the same as ski speed, but not in the turns, for example.

[BraceMaker]

Load is part of work

 

Although really our vectors are wrong. We have tension against a boat and change in angle not force and displacement

 

This thread supposed that a fast ski gets across course faster with less work so data would give you proof or call bs and both skis got there.

[Razorskier1]

Speed requires the "right" load and angle. Think of a sail on a sailboat. Too much angle and the boat goes fast right up until it flips. Same with skiing. I might sometimes generate incredible loads approaching 1000 lbs. Unfortunately, this occurs when the ski has too much angle and I'm literally just yanking with all my might. I suspect that my speed in this case is less than my speed when I am taking the correct amount of angle to generate maximum speed/acceleration with a lesser load. The math -- well, I leave that to the smart guys on this thread.

[DanE]

@Razorskier1 - I was not talking about ski angle but reffering to the rate at wich the rope moves around the pylon, the faster the rate , the faster the handle end will travel.

That would probably be synonymous with skiers speed and top speed should occur when handle and COM are traveling together right before /through the edge Change.

If there was a practcal way to measure this the data could be compared to a skiers perception of a "fast " or a "slow " ski.

I suspect the results might come in as a surprise, would atcually be a lot of fun.

[Mortyski]

Just to let everyone know I have been working on this for a while. I bought a GPS system that supposedly acquires 20 data points per second with a 6 inch tolerance. I also bought a tension measuring device load cell. I also have a magnetic timer to start the data transfer and Dartfish video analysis software. (Dartfish is the wizzy software coaches use for athletic motion analysis.) The plan is to measure the skier path, acceleration, deceleration, rope tension vs time in a slalom course and plot everything on a Dartfish video. Each skier will have their own fingerprint of when they pull, how hard they pull where and what acceleration / deceleration / speed they carry in the course as well as where they are in the course vs time.

 

If you belonged to the Nichols Forum in the past you might of read about this system...we called it Lisa 2.

 

The "evil" plan I had was to revolutionize ski instruction by getting scientific about what worked. From this data we could even do a better job of designing skis....and of course we could then define a slow ski and a fast ski

 

I have been trying to get this going for a while. I'm an engineer but I cannot create the computer data acquisition program.

 

If you have some interest in this development let me know.

 

my best,

Murray (Mortyski)

[Skoot1123]

@bracemaker @Than_bogan @mortyski - I have been thinking about this since it was brought up as well. My idea might be simplistic, but I believe it has some merit, and what is learned can then be used as the basis for expounding it.

 

Here goes: mount an angular measurement device on the ski pylon, take an accelerometer and bury it inside the handle, load sensor on the rope, very accurate speed measurement for the boat, boat path deviation measurement (nice to have), the standards (air temp, water temp, humidity), and a data acquisition system that can sample at a very high rate. I'm thinking 10,000 kHz. Why so high? Why not! Filters can be applied to reduce the noise where needed. When I worked at the proving grounds for CAT (number of years ago) 10,000 kHz was not uncommon. We would use that when trying to understand dynamic frequencies while shifting. Futher, another couple runs could be run at 1,000 kHz or a little higher to compare and use as a baseline.

 

Perhaps one thing we are overlooking is the perception of speed that was mentioned above, if a ski is able to accelerate quickly and slow quickly then it may "feel fast" whereas a ski that carries that speed ACROSS (not down) course and through the turn may not "feel fast" but since it is efficient (keeping speed up) will make the pass feel easy. Are we not all looking for the ski that makes the course feel "easy?" Obviously there will be the next challenge - shortening the line but that's what we are all after right?

 

Hope at least some of this makes sense. I don't have the level of technical expertise that many other folks have on here - I'm just an engineer addicted to skiing!

[BraceMaker]

@skoot1123 - I like the accelerometer. I agree, I think what I want is to put data to perception. THings feel fast and aren't, things feel easy - but maybe were actually under more load while being stable instead of actually faster or easier.

 

In the end, I think data would be cool, imagine having your youtube videos display line load and skier speed, or overlaying your acceleration like the in-car G-force sensors in F1?

[Skoot1123]

@bracemaker - that would be awesome! A display of speed would be neat too. (though at my level of skiing it wouldn't be all that cool....lol!)

[DanE]

@Skoot1123- Spot on! I suspect that some Skis that are considered "fast " is actually effiecent slowing down and also accelerate therefore creating an illusion that it 's fast since acceleration can easily be felt while speed really cannot be.