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  • An Introduction to GUT: A Scientific Approach to Slalom Skiing



    Written by: Adam Cord and Adam Caldwell


    Path of Handle Relative to Pylon
    The purpose of this image is to illustrate how far forward, or what we call %E2%80%98high up on the boat', the skier must advance in order to reach the buoy. %E2%80%98High on the boat' is a term we use to describe the distance between the skier's position and the horizontal plane of the pylon. When the skier is at the centerline (CL) of the course they are as far behind the boat as they will ever get. Conversely, when at the turn buoy, the skier is as %E2%80%98high on the boat' as they will get.

    Down-Course Speed
    The geometry shown also helps to highlight something interesting about the down-course speed of the skier as it relates to the boat. If we look only at the direction of boat travel (down the course); when a skier is directly behind the boat (at CL), they are always moving down-course at exactly the same speed as the boat. This is true no matter how fast or slow they may be moving across the course (side to side or tangent to the circle).

    Keeping that in mind, we can also see that while the skier is moving from the buoy to the centerline, as they are building cross-course speed, they will always be going slower than the boat in the down-course direction. Additionally, when moving from CL to buoy, they are always going faster than the boat in the down-course direction. There can be no exceptions to this rule, and it's an important one to help us better understand our technical objectives on the water. What does that mean with regard to line length and skiing difficulty?

    The Increasing Difficulty of Shortening the Rope
    Let's start by looking at the full length rope, 23 meters (75ft). When the skier is directly behind the boat at CL, he is 23m + arm length away from the pylon, or roughly 24 meters. In order to reach the buoy he must swing outwards and also move upwards on the boat by 2.9 meters. After reaching apex and turning the buoy, he must then be slowing down in order for the boat to move ahead by 2.9 meters as he moves back to CL. Being that 2.9 meters is a short distance, the down-course speed of the skier at nearly all times will be very close to the speed of the boat at this line length. Because the speed variance of the skier is low, the acceleration/deceleration rates are low, the loads are low, the pressure on the ski is low, and the overall level of difficulty is low.

    Now let's consider 10.25m (41 off). This is an extremely short line that only a handful of people in the history of the sport have ever run in a tournament. Therefore, running this pass is incredibly difficult. Just as with long line, the skier will be going exactly the same speed as the boat at CL in the down-course direction. Also, just as with long line, when considering only down-course direction, the skier is moving slower from buoy to CL, and faster from CL to buoy. The big difference is that after accounting for reach and arm length, the skier must travel nearly 11 meter (36ft) %E2%80%98higher on the boat' to be able to reach the buoy! That's an incredibly long way in a very short amount of time. After turning around the buoy, the skier must again slow down enough to allow the boat to advance 11 meters ahead as he skis back into CL.

    In order for a skier to complete a pass within the constraints of the slalom course at the 10.25-meter line, the variance in down-course speed is huge! They are traveling significantly faster than the boat in the down-course direction from CL to the buoy, and much slower from the buoy back into to CL. That means the rates of acceleration/deceleration will be extremely high, the loads extremely high, the pressure on the ski and rope are extremely high, and thus the level of difficulty is extremely high. No wonder such a small number of people have ever run this pass!

    Geometry of Slalom
    So now that we have the basic understanding of why the difficulty increases as the rope gets shorter, can we define our true goal? Maybe not just yet. The next key to understand is the layout of the slalom course itself.

    Specifically, we need to understand the distance between each turn buoy both width and length-wise. The course is 23 meters (75 feet) wide, meaning that once you make a turn, you have to travel at least 23 meters perpendicularly across the lake in order to clear the next buoy. That may seem like a long way to go, but consider that there are 41 meters (135 feet) between each buoy when measuring straight down the course. That means the distance we travel down the lake is almost twice the distance we travel across the lake! This also means that, on average, we must travel down the lake much faster than we travel across from buoy to buoy. Knowing this fact, we can begin to look at the %E2%80%98moving parts' of slalom, namely the skier and the boat.

    The Skier, the Boat, and the Course
    On the water there is a boat which travels in a straight line at a set speed and a skier which follows the boat at the end of the line, traversing through the course. Generally speaking, the skier simply moves side to side, attempting to get wide enough to clear the buoy, and moving from one turn to the next within the time constraints dictated by the boat speed.

    As we know, this becomes more and more difficult as the rope gets shorter because the skier must travel a greater distance with respect to the boat over the same fixed time. To do so at short line, the overall difference in down-course speed must increase greatly between swinging up %E2%80%98high on the boat' and then slowing down to turn close to the backside of the ball. Again the loads, forces, and more dramatic change in direction at the bottom of the swing at CL make it that much more challenging each time the rope is shortened.

    So, knowing what we have learned thus far about the geometry of the course and the skier path relative to the boat, let us stop and think about a scenario. You are rounding the buoy and now at the slowest speed you'll be both down-course and cross-course. The boat is moving down-course much faster than you are at this point in time. What is your ultimate goal here? Get wide to the next buoy? Get early? Neither.

    Ultimately, what we really have is a race between the boat and the skier. To win, you now must try to get DOWN the lake to the next buoy as fast as possible. To run the course successfully, this process of racing against the boat must repeat six times without losing control and position. Learning to accomplish this is the biggest challenge any skier will face. Here is where GUT comes in.

    The Grand Unified Theory: Defined
    Everything we are trying to do in the course can be directed to support one simple and logical objective. All of our thoughts, actions, movements, and efforts can now be executed to support one simple goal. We will look to accomplish this from the very first instant of our pullout for the gate, and then repeat it six more times through the course. There is one dynamic that is paramount to success in slalom skiing. It is the only thing we need to focus on, and the one thing we can build our entire philosophy, technique, and understanding upon. Our objective is to:



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