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GUT-103: Moving with Efficiency
Horton
Posts: 32,395 Administrator
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).
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.
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.
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).
 |
| 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.
 |
 |
| 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
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...
Goode / Centurion Boats
Most of us need to move our COM forward over the ski in order to achieve the centered balance described by the Adams above. If your bindings are to far forward when you explore this forward move, the ski's tip will develop too much bite. You'll experience a lot of tip-grab that will either throw you OTF or crush you. In other words, this binding-forward setup will be giving you negative reinforcement for making a correct move, making it impossible to form new good habits.
On the other hand, if the bindings are a bit too far back, you will have to move even further forward on the ski than usual in order for your COM to be normal to the ski. In this case, your ski will respond with better acceleration and turning performance every time you move forward, providing positive reinforcement for making the right move which supports the formation of new good habits.
Though it may seem counter-intuitive, having your bindings a little too far back will support your efforts to move your COM forward on your ski better than having your bindings too far forward.
I found one aspect of this to be especially enlightening, even before I had a chance to try it (mostly at the gate when in FL with Team Denali):
There's been a lot of talk of how top pros are forward at the wakes. My previous/naive understanding of that made it seem like it required about 20x more courage than I have to even try. Holy OTF, Batman!
But forward isn't quite what's going on. It's "simply" that they are always normal to their ski. But there's an illusion happening: Behind the boat, the ski is "rolled" away from the boat, but the easy thing to forget is that in the plane of the water it is "only" about 45 degrees away from heading straight at the boat. If your body just comes straight up off your ski in that position ("normal to plane of ski"), then in a picture taken from the boat you will appear to be significantly forward. (You might need to find something shaped like a T and hold it out in front of you to believe me. Angle the "ski" to 45 and then lean the "skier" away.)
That's not a dangerous, about-to-OTF position -- that is dead on centered on the ski!! So now I think about it much more as "staying with the ski" than as getting forward.
I'm not saying I can do it yet, but I no longer think I'd have to be a slightly foolish 20-year-old to have a chance. And actually, I found doing this on the gate pullout to be borderline easy. Wildly unintuitive since I've been doing it wrong forever, but easy enough to execute if I did exactly as told.
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.
I look a lot more like figure 2A on what I would have prior considered a good day.
The notion that the lean is in relationship to the boat, or in other-words, that you are "leaning away from the boat" causes a tremendous amount of issues because the frame of reference is WRONG. That is exactly the same leaning back, or uphill, in alpine skiing. Anyone who is a snowskier knows how bad that is for your skiing - the "eternal tail-ride" that is impossible to get anywhere and improve with. (The bindings also plays a very significant role, and was raised in a previous thread, boot-performance).
The frame of reference for the skier must change. Its not about moving relative to the boat. It is about moving relative to the ski. Your "lean" must always be relative to the ski and nothing else. If your lean on the ski is always within the 90 degree normal target plane, you are never forward and never back, only leveraged laterally over the edge, as @Than_Bogan highlighted above. An overhead view of the skiers would help to highlight that dynamic and will be presented in GUT Level 300 material.
As @AdamCord mentioned, these Level-100 discussions are intended to be very simple, introductory topics that are digestible. More info will be presented that will continue to clarify the philosophy and build upon the bio-mechanics of "how" to accomplish this objective in a safe manner.
We are interested to have feedback - good or bad. Please PM either @AdamCord or myself. These articles are written for the skiing community not ourselves, so we want to know what we can do better. Its no secret this is challenging to do, as there is a LOT of information. If anyone sees a mistake or a specific area that is not at all clear, please let us know so we can update the articles on the Denaliskis.com website and keep things as clear as possible for others moving forward.
Now the only question is who is Jobs and who is Woz.
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.
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.
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.
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.
(Phew just saved myself from suggesting "trailing arm pressure")
(Just love all this body mechanics!)
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.
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.
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.
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.
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.