GUT-103: Moving with Efficiency

HortonHorton Posts: 32,395 Administrator
edited February 2016 in Technique & Theory
Written by: Adam Cord and Adam Caldwell

This is the third chapter in the Introduction to GUT series.

This chapter discusses a few concepts behind “moving with efficiency” on a slalom ski. Top level skiers have the ability to travel extremely fast behind the boat and carry a lot of speed throughout the course. They can do so mainly because they move with good Center of Mass (COM) positioning over the ski, not because they have super human strength.

The Skateboard Example
When riding a skateboard, your COM must be very close to perpendicular, or what is called “normal”, to the board in the fore/aft plane. As long as your COM is positioned somewhere between both feet, you will be fairly well balanced. To turn the board, you simply shift your weight laterally while still maintaining your COM position in that normal fore/aft plane and the board turns and moves with you. However, if you lean mostly on the back leg as you turn, with your COM behind the rear wheels of the skateboard (like the infamous “drop to the tail” style turn on a water ski), the board will shoot out in front as you fall to the ground. In this situation, thanks to gravity, your COM moved in a direction no longer supported by the board.
In slalom, positioning your COM in the normal plane on the ski is the key element to achieving efficiency in the course. Even though it is possible to ski the course with your COM positioned toward the tail, relying excessively on the rope for support, a tremendous amount of effort is wasted. With enough strength it is possible to survive at longer line lengths with a “back seat” COM position, but progressing into shorter line lengths will be extremely challenging.

The Efficient COM Position for Slalom

Let’s look at what an efficient position should look like on a water ski. From a side view, the COM should be positioned over the ski such that a line drawn normal to the ski’s top surface would pass through the skier’s COM, similar to what is described in the skateboard example above. Additionally, this normal axis must intersect the ski at the midpoint between the balls of the front and back feet. The overall attitude of the ski as it rides in the water is primarily controlled by the location of your COM over the ski. Settings can be used to fine tune the ride characteristics, but the COM position is the primary factor. Figure 1 below shows how the ski attitude flattens out as the COM moves from a back position (red circle) to the target normal plane (green circle).
GUT 103 Figure 1 Rev 2
Figure 1: COM Position and Efficiency

There are significant disadvantages when the COM is either too far forward or too far back. If the COM moves too far toward the red zones shown in Figure 1, it causes the ski to ride with an inefficient attitude in the water where there will be either not enough lift, or excessive drag.

COM Positioning for Balance
An additional benefit to this position is the improved ability to balance on the ski. Your body senses pressure through the soles of your feet, and uses that information to help you balance. With your COM positioned between the balls of your feet you have effective use of sensory input from both feet, in addition to the ability to articulate both knees and ankles productively, which greatly improves your ability to maintain balance. When your COM shifts too far forward or too far back, your ability to balance diminishes greatly.

TEST: COM positioning can be easily tested on dry land to help understand how much it can benefit or hinder your balance. Stand up tall with your feet in line like you would on a slalom ski. First lean back and put your COM over the heel of your back foot. Notice how your balance feels, and how difficult it is to hold a steady position. Now shift your COM forward, by flexing at the knees and ankles so that your COM is balanced between the balls of your feet. There is a huge difference in fore/aft balance, lateral stability, and your ability to control and change positions athletically when you stand like this. This is the same stable feeling you want on a slalom ski. Just like being too far back, shifting the COM ahead of the ball of the front foot will also reduce balance, and more importantly make you more susceptible to an out-the-front type of fall.

Application on the Water
A real life perspective of the normal plane is represented in light-blue in Figure 2 below. In both pictures, the normal plane is located at the midpoint between the balls of the feet. The red dot in Figure 2: A shows the skier having his COM too far behind the target. In Figure 2: B, the green dot shows the skier’s COM being at the target, which is an extremely efficient position.
GUT 103 Figure 2 A GUT 103 Figure 2 B
Figure 2: A: “Back” & inefficient – COM over back foot      B: Forward & efficient – COM at midpoint between balls of the feet.

With his COM further back, the skier in Figure 2: A is putting the ski between his COM and the boat, effectively putting the brakes on. This “back seat” position causes the resulting ski attitude in the water to be tip high, with the tail digging, and the water-break very far back. His effort is being wasted plowing water and fighting the boat. This ultimately reduces cross course acceleration while increasing load.

With his COM significantly further forward and within the target normal plane, the skier in Figure 2: B gains the benefit of having much greater leverage over the ski’s edge, further driving the tip down, rolling the ski to a higher bank angle, and putting more ski in the water. This greatly improves cross-course acceleration and increases the speed at the course center-line. With this high speed and reduced load, he will be able to transition to the turning edge much earlier and more easily, with ample energy to achieve the primary objective of GUT (i.e. taking the handle as high on the boat as possible as fast as possible).

Utilized effectively, ideal COM positioning will help you greatly reduce load, increase cross-course acceleration and improve both fore/aft and lateral balance in the slalom course. Positioning your COM to be near the target plane requires general awareness more than physical effort. Doing so will help the ski carry speed and keep you moving in the direction you want to go, without having to rely so heavily on the rope for support. Being able to enter and finish a turn with the COM in an efficient position will significantly improve your ability to sustain that position into the first wake, and help you accelerate much faster with far less effort.

Summary
It is extremely important to keep the COM “normal” to the ski and balanced between the balls of your feet at all times, regardless of the attitude of the ski in the water, where it’s pointing, or where you are in the course. Skiers who habitually lean too far back are in the red area shown on Figure 1, and this is a hard habit to break. Shifting the COM forward to an efficient position within the green zone on Figure 1 can be unnerving and unfamiliar at first. As awareness and confidence improves, having your COM centered over the balls of your feet becomes more natural. Maintaining ideal COM position will help you transfer the tremendous power of the boat directly into speed and acceleration with much less effort, allowing you to carry more energy through the turns and run an early, wide, up-course rhythm.

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Comments

  • ALPJrALPJr Posts: 2,821 Mega Baller
    edited February 2016
    Good job. The diagrams and pic's remind me of what Mike Suyderhoud had skiers working on at his Shasta ski school in '94/'95 and later in the West Coast Slalom video with @MarcusBrown and @twhisper. Mike likened the COM to how you move in skateboarding too. He told me to change edges sooner and to be strong through the edge change. It was a new way of thinking for many of us who used the turn - pull hard - turn method. Some of the guys at Berkeley called it the trip lean pull, because they were used to rearing back on the ski, and Mike had us moving forward on the ski in the direction of travel.
  • Mateo_VargasMateo_Vargas Posts: 948 ★★★Triple Panda Award Recipient ★★★
    I saw some epic stacks from guys trying the trip lean!
    Success is failure that just hasn't happened yet
  • Razorskier1Razorskier1 Posts: 3,425 Mega Baller
    Given my historical position, which I suspect is similar for many of us, I had to think about trying to get my COM ahead of the ski in order to get to the right spot on the ski. When I got it, I couldn't believe how much more speed I generated both on my first move up for the gate, and at every subsequent wake crossing.
    Jim Ross
    Than_BoganAdamCorddrewski32
  • AndreAndre Posts: 1,791 Mega Baller
    edited February 2016
    Is moving bindings forward a good thing to help achieve this position or is it only a band aid?
    Should i put more weight on the front foot then the rear or is it 50-50% ?
    When trying to shift my COM forward, i feel that i,m pushing on my back leg and digging the tail even more...
    What's the right way to achieve this position?

    Trying to break old bad habits here...
    My ski finish in 16.95 ...but my ass is out of tolerance!
  • WishWish Posts: 8,540 ★★★Triple Panda Award Recipient ★★★
    Don't listen to them. This is still all just a Hoax. I've tried all this stuff with disasterous results. My skiing has tanked from reading this stuff. ;-)
    >>> 11.25..a different kettle of fish. <<<
  • MISkierMISkier Posts: 3,439 Mega Baller
    I think the biggest trick to getting this right for the non-pro is to avoid getting your shoulders slumped forward and/or allowing handle separation from your hip. They may think their COM is forward, but, in reality, they are just plain forward.
    The worst slalom equipment I own is between my ears.
    Wishbishop8950adamhcaldwell
  • AdamCordAdamCord Posts: 1,060 Open or Level 9 Skier
    edited February 2016
    Once we get the base GUT articles posted that explain the theory, we'll start with the more specific "How-To" type articles. We didn't want to jump to the how-to without getting the GUT theory out, because that's not the point. We want people to understand what they are trying to do and why, not just what some article said about body position because that's what's popular right now.

    There are a few key factors that will really help or hurt progress in trying to get your COM positioned right. @SkiJay did a nice job of explaining boot positioning. That's not to say everyone should go move their boots back first though. In fact most skis will work best with the boots as far forward as possible, but obviously there is a limit and there is a sweet spot for every ski and skier.

    A big factor in this is bindings. You must be able to flex your knees and ankles forward and pressure the balls of your feet to do this well. @adamhcaldwell did a nice writeup HERE on boot performance that gets into this. Many people physically cannot get to an efficient position because of their binding setup. If you look at the two images above of the good looking guy (me) in the side by side comparison, you can see that my ankles are flexed a lot more relative to the ski in the image on the right. Those shots were taken a few months apart, and while I'm using the same reflex boot/rtp combo in both shots, I made some extra modifications in the months between that allowed me to flex my ankles more in the image on the right. Both my ability to move to an efficient position, and my balance improved when I was able to let my ankles flex forward more freely.

    @MISkier also made a good point about body positioning or "stacking". We will get pretty in depth with this as well as it is extremely important. In order to effectively transfer energy from the boat into acceleration, you must be positioned in a way that will allow you to maintain this COM forward position even with the rope loads really get high. You also need to pressure the ski in a way that it's position remains as efficient as possible, and also so that it can still increase the rate at which you are rotating the handle around the pylon.

    For now though we just wanted to lay the groundwork for higher level concepts, and understanding where the COM should be and why are an important part of that.
    Razorskier1MISkier
  • 6balls6balls Posts: 6,081 Mega Baller
    I feel that if I looked like figure 2A it would have been the "sense" (old school now) that my ski didn't completely finish under me, leaving me on the nose...and by the time I'm at the wake I'm going OTF. Trying to wrap my brain better about this new concept.

    I look a lot more like figure 2A on what I would have prior considered a good day.
    Dave Ross--die cancer die
    adamhcaldwellOne_Ski
  • WishWish Posts: 8,540 ★★★Triple Panda Award Recipient ★★★
    I have modified my home brew boots for forward travel recently based on the above. The difference is night and day. Took a few passes to get comfortable but then it felt great. More in control with an athletic/dynamic feel and now when I don't get my COM forward it is obvious...especially out of my off side. BTW...it is very cool that the Adams are willing to share all of this.
    >>> 11.25..a different kettle of fish. <<<
    adamhcaldwell
  • Razorskier1Razorskier1 Posts: 3,425 Mega Baller
    @6balls - that's what I refer to as "hiding behind my ski". It feels safe and comfy, but it overloads the line and doesn't build speed. OTF tends to be from overload, with the load then transferred forward to where you can no longer hold it. Done correctly, I actually am now trying to "get ahead of the ski" right from the hook up. Doing so keeps the ski moving and keeps me on the accelerator. So even though you are more forward COM than you are used to, you don't go OTF because you generated more speed than load.
    Jim Ross
    WishadamhcaldwellThan_Bogan
  • ToddFToddF Posts: 604 Solid Baller
    @adamhcaldwell @AdamCord You guys are reminding me of what happened back in the 70's at PARC. And we all know how that turned out.
    Now the only question is who is Jobs and who is Woz.
    adamhcaldwell
  • 6balls6balls Posts: 6,081 Mega Baller
    @adamhcaldwell sometimes saying the same thing differently and it hits home...that really resonated with me above as you wrote about not leaning away from the boat. Geez my entire life has been leaning away from the boat and relative to the boat not to the reference of the ski and it's path. Very helpful way you explained that concept above.
    Dave Ross--die cancer die
    adamhcaldwell
  • adamhcaldwelladamhcaldwell Posts: 835 Open or Level 9 Skier
    edited February 2016
    @6balls - ALMOST EVERYONE IS IN THE SAME BOAT. The top level guys have inherently figured it out, whether they understand what they are doing it or not is a different question. Its a big part of why they look so different on the water compared to novice/intermediate level skiers.

    It is true that once the ski has a significant angle of attack and you are behind the boat, that you are actually leaning away from the boat to some degree. However, it does not necessarily mean that you are over your feet and on top of the ski in a way that forces the ski into a more efficient and productive attitude in the water.

    If you lean away from the boat anywhere near the buoy line, its a guarantee that you will fall to the tail and get stuck plowing and dragging with a lot of unproductive load all the way into CL, killing any chance of creating "swing" out off the second wake.

    Changing the frame of reference for moving dynamically on the ski is a game changer, regardless of what level skier you are.
  • ktm300ktm300 Posts: 453 Solid Baller
    Wow. Thanks Adams. Such great, understandable explanation and illustration of concepts. Where do we sign up for the Denali ski school? Ski language is wacked. Not much of a common vocabulary leads to much confusion. Are they saying the same thing in a different way? Who knows? I'm thinking you guys are establishing the dictionary, the common meaning.
    adamhcaldwell
  • adamhcaldwelladamhcaldwell Posts: 835 Open or Level 9 Skier
    Not to steer this discussion the off topic... but, we organized the first test of a "Denali Summit" this past November in WestPalm, FL. It was a tremendous experience for everyone involved. @Razorskier1 @Wish @Than_Bogan and others made the trip and were our Test dummies for how we present the information.

    We plan to host additional "Denali Summit" events throughout year. We will be organizing dates and presenting the information on Denaliskis.com for the event in the near future, so stay tuned.

    Spaces will definitely be limited, but the objective is to spend at least 3 days with a small group of people focused specifically on GUT. Given there is so much to go over, we hope to have enough info documented this spring that people can learn/digest the higher level concepts independently before arriving. This will significantly streamline and improve the on-water learning experience during the Summit.

    There is always more then one way to get from point A to B. But whats important is HOW going from A to B sets you up for hitting the next target, C.
    Than_Bogan
  • 6balls6balls Posts: 6,081 Mega Baller
    @adamhcaldwell very true. I figured out some time ago 90 degrees cross course is not the goal and that I could be more efficient...man I skied with serious load a ton of power was necessary to get down the line.

    I've gone to more efficient angle out of the ball, trying to move my upper body inward toward center line out of the ball to stay over the ski. It's helped my tourney PB was at age 40 of all things.

    Having said that in still frames taken last summer I lean away from the boat immediately out of the ball, rear the ski up for a moment, then put it back down where it belongs and get after it in what I thought was decent stack...though it looks a lot like figure 2A still leaning away from the boat and COM too far back.

    Very helpful for me to think about first proper angle of attack for the ski, and then leaning away from that cross course angle rather than leaning away from the boat as if the ski is on a 90 degree cross course track.

    Cool stuff...and I agree with others if you develop a common language we can all speak and concepts we understand in a consistent fashion...we all get better and our discourse between skiers makes SO much more sense. So often I don't "get" what another high end skier is describing and vice-versa. This is cool stuff you have going here.




    Dave Ross--die cancer die
  • Chef23Chef23 Posts: 6,066 Mega Baller
    I know it is right but position 2B scares the hell out of me.
    Mark Shaffer
    HortonDeep11Andre6balls
  • aupatkingaupatking Posts: 1,787 Mega Baller
    Thanks @AdamCord . You must have said it 6 times in your article, "weight on the balls of your feet". Not until @adamhcaldwell put out that info on his reflex setup did I realize how much I was not on the right part of my feet. I kept trying to get forward but didn't realize how much my boots were inhibiting that motion, and what that meant down the line. I'm not blaming my boots, it was a mixture of me using them incorrectly, and needing to do some modification. I was running the top buckle too tight, to make dead certain they'd release. While that worked for that end, it absolutely did not allow proper forward flexion.
    I've been trying one modification at a time and, with very limited ski time (cold), I've seen very promising advances in position, RELATIVE TO THE SKI. It felt great and outbound glide is an easy byproduct. I didn't realize exactly what I was doing differently until now.
    I'm straddling both topics here, but really wanted to thank you guys. This series is giving us all a greater ski education. I'm seeing results.
    WishadamhcaldwellAdamCord
  • Deep11Deep11 Posts: 247 Solid Baller
    @Chef23 totally agree but I think what makes it work is that you can see the right shoulder and right hip in pic2 and the handle is close. I think a world of pain could open up if you used the position in pic1 to do what is being done in pic 2 :)

    (Phew just saved myself from suggesting "trailing arm pressure")

    (Just love all this body mechanics!)
  • AdamCordAdamCord Posts: 1,060 Open or Level 9 Skier
    edited February 2016
    @Deep11 overall I agree with you. That being said, it's amazing what you can get away with if you've got speed and you manage to keep your COM from falling back. This is why having the ability to bend at the ankles is so important. It allows you to get to where you need to be, even when things are going south.

    I don't want to get into a long discussion about Nate Smith and his technique, but a big part of his amazing consistency isn't that he never makes mistakes, it's that he is able to put himself in a position to still be efficient when he does make mistakes. For instance, when he is skiing smoothly his wake crossing will look like this:


    He's in a very efficient position here, with his COM very well balanced and forward. But that's when everything is going well.

    When most people get in "deep" and get separated from the handle coming out of the buoy, they get stuck on the back of the ski, leaning away from the boat. As we said this is an inefficient place to be, and it causes the loads to increase a great deal while acceleration is reduced.

    Nate, on the other hand, deals with this by having the ability to very freely bend at the ankles. This allows him to get his COM back to an efficient position, even when he's lost control of the handle. The result is that he's still able to move up on the boat quickly before the next buoy and stay in the pass. This shot is from a 41off pass that he RAN. Notice how much his ankles are bent, and even though he has completely separated from the handle, he has still managed to stay efficient by keeping his COM between the balls of his feet.


    Chef23Than_BoganWishTexas6
  • SkiJaySkiJay Posts: 2,314 Mega Baller
    Picture 2B only looks frightening because it's a still photo in the middle of a dynamic move.

    At the ball, the ski is way wide of the handle. At photo 2B in the first white water, the ski is moving across the course faster than the handle. A fraction of a second later near centerline, there would be no apparent forward lean at all. And at the second white water, the ski will have moved past the handle on its way to being way wide of the handle again at the next ball.

    Now if the skier's COM in photo 2B was moving across the course a little faster than his ski, that would be the stuff spectacular faceplants are made of.
    www.FinWhispering.com ... Your ski should be your dance partner, not a wrestling opponent
    AndreBruce_Butterfield
  • Than_BoganThan_Bogan Posts: 7,043 Mega Baller
    edited February 2016
    So here's a statement that's easy to make in the winter, but I'm hoping is true:

    If you try to CATCH UP with your ski near the centerline, you will faceplant. But if you STAY with your ski at all times, you'll be stable and comfortable.

    The former move means pitching forward and pushing down the tip. The latter move means you are dead center over your ski the entire time.

    My plan for learning this (subject to change with further coaching) is to really concentrate on where I am on the ski before reaching the wakes, and then see if I can "simply" stay with it as the ski rapidly rotates from almost 90 at the finish to roughly 45 behind the boat to 0 approaching the ball.
    Nathaniel Bogan -- GUT Padawan
    A_B
  • ALPJrALPJr Posts: 2,821 Mega Baller
    edited February 2016
    Good to see slalom theory continue to develop. Google Terry Winter Waterski Lessons (video). There's 4 or 5 in a series that offer a nice explanation of the why. Also look up writings and videos by Brown, Suyderhoud and Rossi.
  • Ed_JohnsonEd_Johnson Posts: 2,303
    edited February 2016
    @SkJjay brings up a very good point. Keep in mind that Nate comes off the Apex with forward COM, allowing him to get ahead of the ski to start with. This starts his acceleration OFF the Apex, which every good Race Car Driver knows is essential.
    Therefore, with that proper COM positioning into and through the Load, the ski will accelerate from behind you to out ahead of you. It is like a slingshot effect.

    When you ask the top skiers about the edge change, they almost always say it's Automatic. That is the reason why. In fact once you set that acceleration in motion, it can feel like your shot out of a canon and you can't stop it from happening.


    Special Thanks to Performance Ski and Surf and the Denali Adam's !!!
    A_B
  • AdamCordAdamCord Posts: 1,060 Open or Level 9 Skier
    edited February 2016
    @Ed_Johnson we've been referring this for a while as getting ahead of the ski and "leaving the ski behind" coming out of a turn or dropping into the gates. I think I first heard of this concept years ago from Drew Ross, but I didn't really understand it until we started to put the GUT pieces together in the last 5 years. But, when you start to think of where your body should be relative to the ski instead of the boat, it makes perfect sense.

    Also you've touched on a big part of GUT that we will get into later about the "automatic" edge change. I don't want to jump right into the geometry and dynamics of why that happens here though, as it is it's own GUT article all by itself.
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