Multivariable analysis and the studs(ettes)

[gator1]

I compared video of Nate, Regina, CP, TW, and Dave Miller. I searched for common moves amongst these 6, and for moves that were not common and were therefore individual characteristics of the skier. My thesis was that only the common moves are dictated by physics, mechanics and hydrodynamics. I tried to be objective, but of course my search was contaminated by 40 years of chasing buoys, and all that I have heard, read, seen, been told, calculated, measured and experienced.

 

The availability of quality video on the studs and studettes enables this type of analysis, which, before utoob and BOS, was pretty much impossible.

 

Dave Miller was the most important test subject as his skiing deviates from the accepted ideal in many ways, and yet his performance is world class. Therefore, what is NOT common between his skiing form and the other 5 subjects is also probably NOT a critical variable. Yes, Dave is an uncommonly gifted athlete, but then so are the others.

 

After finding 8 common moves, and denoting them as critical variables, I ranked the 6 subjects on their implementation of each of the critical variables and averaged the score. Regina ranked first, Nate a close second. Kind of a surprise there.

 

I then combined Nate and Regina's ranked variables to determine a descending order of importance. For example, Nate has a "10" on angular momentum conservation, while Regina has a "10" on turn radius optimization. But neither of those two variables ended up on top when their two lists were combined.

 

So I had a list of the 8 variables in descending order of importance.

 

Then, I analyzed (I love the fact that the word starts with "anal") vids of my skiing, and my bud's. My findings were as follows: we suck. But in different ways. We all get into 38 and beyond, but, as compared to the 8 variables, we suck.

 

So, depending on our IQ and multi-tasking abilities, we are each attempting to improve our critical variable(s), starting with the variable that has our highest combined deviation from ideal and rank.

 

I am able to concentrate on exactly 0.7635 variables at a time, putting me dead last in our group. But, even with that, this has so far been a very exciting spring.

[Than_Bogan]

Sounds like fun! I like the less-than-1 as the number of variables you can concentrate on at once. Been there.

 

I can only barely understand what you've done so far, but I want to know more:

 

- At some point, it would be cool if you can share more details -- maybe in a spreadsheet or something? Some explanation of how to grade the variable would also be pretty huge. Maybe that alone will make all of the following moot.

 

- You note in your post that Dave Miller was very important, but it sounds like your methodology thereafter doesn't use his data at all? Or maybe you used his info only to find "common moves"?

 

- The notion of "common moves" kinda sets off my spidey sense, because it sure sounds like it involves a hard threshold -- and those come with all sorts of downsides, especially when applied in the one of the early stages. But I guess if you keep the list long enough, then maybe it's not too dangerous to threshold relatively early in the process.

 

- The only two categories you specifically name seem pretty vague to me. If I were asked to rate someone's angular momentum conservation, I would have no clue what to look for. But at least I have a basic physics understanding of what that could mean. "Turn radius optimization" is even more problematic for me, because how do I know what the optimal radius looks like? And of course, the turn does not maintain a constant radius, so the optimal is not just some value but is a function vs. time.

 

- Why combine only Nate and Regina's lists? Since they are doing everything well, I wouldn't expect them to be very helpful in determining the order of importance. If there is a class of skiers doing almost everything wrong but excelling at one thing, and getting good scores as a result, I'd take that as a stronger indication of relative importance.

 

- Did you find that any of you mortals had a high grade on anything, or was it more that the gods did everything better?

 

- Last year I managed to catch a video of myself running -38. It was the first time I understood how -41 is possible: if someone can look THAT stupid, do nearly everything wrong, and still run -38, then it makes sense that someone who WASN'T a total dufus could run -41...

[gator1]

Nate and Regina do lots well, but not everything close to perfect. But you're right, including all 6 would be better. But got too complicated.Each of us Spokane mortals does at least one thing pretty well. Just like in engineering multi-var, I graded them on my own standard. Not an absolute, but turns out to be valid approach to multi-var experiments. Dave Miller let me knock out a bunch of stuff, or downgrade its importance, I previously heard/thought/believed to be critical variables. For example, IMO, he sucks at angular momentum, but is best of the six at torque. I could have kept all 6 through the end of the exercise, but it was getting too complex.

 

I posted on angular momentum conservation awhile back.

 

Youre right, if I miss something, and there are 9, and the 9th one is the most important, have to hope it comes naturally or I'm screwed.

 

If this works out for us this season I'll try to distill it. Many of the moves take some explanation from gatoronian semantics to common terms, too much typing work until I know if this approach works.

[Than_Bogan]

Fair enough. Thanks. Looking forward to more.

 

I can appreciate that any self-consistent system of ranking can provide useful information. However, someday I'd love to do something like this with more people -- both as subjects and as graders. At that point some pretty clear definitions of each thing along with how to grade it would become essential.

 

I can probably tolerate gatoronian a bit better than most, so feel free to send me barely parseable drafts via email (and let me know if you lost my email!).

[colo_skier]

@gator1 and @Than_Bogan WOW I am an engineer by employment and I see a thread worthy of the Big Bang Theory. :)

[Than_Bogan]

I recently had someone complain to me that the Big Bang Theory is too farsical and that the characters are overly parodied. I got a good laugh out of that one. I knew all those guys at MIT, and at times I *am* all of them. Of course, real nerds aren't consistently funny, but the general stuff they show on that show is alarmingly real. I still can't believe anyone but us Ubernerds actually watches it, but whatever.

[ForrestGump]

Did you guys get beat up a lot in grade school? ;)

[Than_Bogan]

@ShaneH Nope, I'm pretty fast and I fight dirty. :)

 

Sadly, it also makes a big difference to be moderately athletic and occasionally comb my hair. The people who get picked on the most are the ones that outwardly LOOK like nerds, not the ones that really are to their core.

 

Finally, bullies thrive on intimidation, but I have the ultimate weapon against that: Irrational self-confidence and arrogance!

[gator1]

@shaneH, Ya, we did get beat up a lot IN grade school. Because we made fun of guys with poor grammar skills. Born 20 years early, now I'm told its cool to be a nerd.

[gator1]

@than_bogan, well, since, like half naked skier pics, those who are offended by public nerdity can just skip the post, lets see if my personal weakest variable makes sense:

 

Torque: How much positive torque does the skier create with the ski during the acceleration phase? This is the moment created by the offset of the center of pressure of the water flow on the bottom and edge of the ski as compared to the center of pressure on the top of the ski by the skiers two feet, and the moment about that center of pressure caused by the difference in load between those two feet.

 

Its not just ski in the water. If you get a lot of the ski in the water by standing on the front foot, you can move the center of water pressure towards the front of the ski. This is good, because when the center of pressure is forward, and ahead of the feet center of pressure, the ski is trying to help you get more angle-a positive torque is created. But, since you got more ski in the water by standing on your front foot, you've negated the gains because you've also moved your foot center of pressure forward. And when you hit the wake you are toast.

 

So, the angle of the spray off the ski in the accel phase is a measure of the torque being created by the ski and skier. Very little spray means L/D ratio is good, and most force is going to accel. Lots of spray means more force going to drag.

 

If you accept that Miller and Nate kill the torque category, how do they do that? I think they use the rope as an anchor point, and rotate the tip of the ski down into the water with core, hip, knee and ankles. This becomes an instable system as the ski curvature digs for more angle, and the only way to restore stability is to shove the ski in front of the hips to negate the positive torque as they cross the wake.

[A_B]

8 Moves? I can't focus on 3 things while I am skiing!

[LZywicki1]

3 things are all I can focal on, go right then left and don't fall.

[gator1]

Don't have to focus on all 8. Just fix the broke ones

[A_B]

Like herding stray cats!

[Waternut]

I see talk of 8 variables and a possible correction to 9 variables. I may have missed it despite having read your posts 2-3 times specifically looking for this information but I'm pretty curious why you neglected to mention what these critical variables/common moves actually were and what was common and uncommon between the 6 skiers...

[gator1]

1) Positive torque on ski in accel

2)Shoulders behind chest in all phases

3)Angular momentum conservation

4)G-force conservation around ball-turn radius optimization

5)On side pull vs off side pull difference

6)Convert angular momentum to 14 inch COM movement

7)Speed conservation at hookup

8)Gate is max torque at hookup, not max pull.

 

Those are the common denominators I saw. All IMO. The reference to 9 was discussing the fact that this is IMO, and there may be any number more or less.

[A_B]

Geez, no wonder OB is doing so well. Sounds like a flight check.

[gator1]

Nah. @ob is using voodoo.

[kfennell]

Can you please explain what you mean by torque?

[gator1]

@kfennell I tried 9 posts above yours. That's my best shot .

[Texas6]

Not being an engineer by degree, I take a different approach to this...

 

1.) What line length do they fall at.

2.) What buoy do they round at their shortest rope.

3.) Is it more than me? If yes, they are better.

 

[eleeski]

When I coach I focus on a few things:

Progressive gates (your number 8)

Aim for an imaginary buoy narrower and earlier than the real buoy (6?)

Don't stare down the buoys (3)

Tits up (2)

Soft knees (4)

Tight stomach (6)

Push to finish the turn (7)

Keep turning after the hookup (1)

 

#5 is just a skill and trust thing. Do the best you can on either side.

 

Interesting analysis. Cool that it loosely agrees with what I focus on (in different words). Of course, I am the smartest person on this board! GNAR

 

Eric

 

[gator1]

I can't believe you coach year round. I'm so much better than you.

[jimbrake]

Ha! @gator1 zings @eleeski.

 

Hey @ eleeski - push what to finish the turn?

[eleeski]

@jimbrake Push with everything you can push with. Legs and core to make your body position right and keep the ski coming around. Hopefully you had soft knees at the apex of the turn to have something to work with.

 

Zinged for sure...

 

Eric

[Chef23]

@eleeski maybe I am doing something wrong but I have an issue with push to finish the turn. I can see push after finishing the turn but if I think about pushing to finish the turn the ski stalls for me and doesn't come around the way I want. I have been coached to be patient and don't push to finish the turn.

[jimbrake]

@eleeski - doesn't the ski turn on it's own if it's on edge (both rolled up on edge and a sufficient length of edge engaged) and moving? Pushing to me implies pushing the ski forward - as in out from under you. So, right when you want to be in a position to accelerate, a push might be putting on the brakes. No berry good. Now if you are "pushing" your core forward, without leaving your bum behind, then that is good!

[eleeski]

Forces at the hookup work to pull you out of a good body position. It takes effort to avoid ending up in a bad position. Gliding patiently around to the right position cures some problems but that is not a max performance approach ( @Chef23 , often patience is what I will coach to fix a problem but it is not a fundamental to me). Ride the turn all the way around for sure - but put some effort in it.

 

@jimbrake‌ The ski on edge does the turning for you only at the start of the turn. Push to get some extra once the turn is done. Maybe if I say "kick the ski in front of you out of the turn and make sure your core stays with it" the point might be clearer (but more words to remember late at 4 ball). Don't get back on the ski or stomp on it to get too far on the front - body position is always critical. Push everything to accelerate cross course.

 

Eric

[ForrestGump]

You guys forget that you are talking about the inventor of the Lee-Ski. It's very well possible that he HAS to kick it out in front of him. ;)

[Lieutenant Dan]

@gator1 Unfortunately I let my nerd card expire a long time ago (Masters in Aerospace Engineering in '87 followed soon after by a career change to the dark side, i.e. sales) so I am not quite following your item (1) and explanation of torque on the ski in acceleration (but for some reason really want to). Torque around what axis? Accomplishing what rotation? Are you saying they net some positive torque which results in the ski creating increased cross-course angle as they accelerate?

[gator1]

@lieutenant Dan: Yep..torque around an axis perpendicular to the ski surface, penetrating the ski between front and rear foot.

 

I am saying they at least net less negative torque (negative torque defined as tending to rotate ski towards boat, forcing body to hold ski cross course using rope as leverage point), and it feels to me like a net positive torque as the ski wants to head towards the wake of its own accord.

[Than_Bogan]

#ForeheadSlap! I've been on the wrong damn axis the whole time. OF COURSE you meant around an axis perpendicular to the ski surface because that actually makes sense. Now at least I understand 1 of your 8 items...

[gator1]

Ah, cmon @than_bogan. My stuff always makes sense even though its often wrong.