GUT 101



When we started skiing together years ago, we, like most ski geeks, wanted to try and understand the science behind water skiing. Digging deeper into ski design, we struggled to define our goals and objectives for how a ski should perform without an understanding of what a skier should be doing technically on the water.  While there are many ideas about slalom technique, we had never heard a clear philosophy of slalom theory and technique based upon physical science. If you look closely at other sports, you will find that there are sports scientists that have taken the time to define the movements of their sports within the realm of physics, dynamics, geometry, etc.  We have set out to do the same in our sport.  The following is intended to serve as an introduction to the physical science of slalom: The Grand Unified Theory of Slalom.

Definition:  Grand Unified Theory of Slalom (GUT); a global model in which philosophy, theory, and technique are defined to support a singular universal objective; one that functions for all speeds and line lengths in slalom water skiing.


Introduction – Why GUT

The general intent of slalom skiing is to run the course successfully by executing a series of movements that flow together seamlessly.  The question is, “Where do we start?”

Historically, skiers invest tremendous amounts of time attempting to link multiple, seemingly unrelated, theories (i.e. counter rotation, swing, connection, handle control etc.) with various techniques (i.e. hips up, open-to-the-boat, back-arm pressure, level shoulders, stack, etc.).  These moves are very complex and hard to master. Some concepts are great and others are not. How do we sort them out? How do we piece these seemingly individual and disconnected ideas together?

The issue is, there is no governing philosophy rooted in physical science that can bridge the gaps between existing theories and techniques.  We need a better way to unify technical concepts, and a new way of understanding the independent complex movements as a singular dynamic process.  With a deeper understanding behind the physics and geometry of slalom, and the ability to integrate all theories into one universal model, it then becomes clear what our objective as a skier must be.

This article is intended to introduce and highlight a few simple concepts, define our objective, and begin to peel back the layers of a much deeper, highly detailed philosophy of waterskiing that is based solely and firmly on science.



We will start with a simplistic view. We all want to go around six buoys with the shortest rope possible. Simple enough, but what does that translate to for applicable technique on the water? Maybe you should counter rotate more? But how or when? Or perhaps you need to edge change sooner…or later? How do we begin to investigate what’s really going on and where to even start?

Before we can understand the technical movements on the water, let us begin by looking at the geometry of slalom from a new perspective.  By this we mean a two-dimensional, geometric view of what events are taking place that you would see if you were floating 1000 feet above the lake and watching someone ski through the slalom course.  Similar to standing over a pool table, looking down from above, and visualizing your next shot based on the geometry laid out between the balls, bumpers, pockets, and constraints of the table.  This is where we must begin, as geometry is the most fundamental part of skiing.


The Importance of Geometry

As a skier improves, he or she will generally increase the boat speed until the maximum required speed is met. The level of difficulty increases in a linear fashion along with speed. Once the maximum speed is reached, a skier will then begin to shorten the rope as their ability improves. The level of difficulty then increases exponentially as the rope is shortened.

The ‘standard’ line lengths have been changed and adjusted over the years in order to compensate for this exponential change. Smaller and smaller sections of rope are removed from one shortening to the next. The first section is 4.75 meters, followed by 2.25, 1.75, 1.25, 1, 0.75, 0.5, 0.5, 0.5 meters.  The real question is, why does skiing the course become so much harder as the rope gets shorter?

The image below is a simple representation of the path of the skier and handle relative to the boat at various line lengths. For the sake of clarity, not all rope lengths are shown. The arc of the 23 (long line), 16, 13, 11.25, and 10.25 meter ropes can be seen below. These arcs represent the rope length, plus 1 meter to account for overall reach.



The purpose of this image is to illustrate how far forward, or what we call ‘high up on the boat’, the skier must advance in order to reach the buoy.  ‘High 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 ‘high 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) ‘higher 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 ‘moving 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 ‘high 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:


This is the Grand Unified Theory, or GUT for short. Everything revolves around this one concept.  This is what drives our technical efforts to generate the speed, timing, and swing required to run each line length.  The concept works at every speed and line length. Every action, thought, and effort must be made to support this objective. 

With a clearly defined objective we can focus our vision and search for a deeper understanding of how to accomplish this dynamic on the water. Now we can use the principals of geometry, physics, and dynamics to govern and define what our actual “technique” must be.  Confusion of opposing ideologies that exist today will slowly fade, as we now have a way to filter, and sort what is right, and what is not.



GUT has been written to document and share knowledge with the rest of the skiing world. By exploring a higher level of understanding defined by philosophy rooted in the undisputable facts of science, we hope to help everyone experience slalom skiing in a new way. Learning GUT will help anyone, whether skiing the course for the first time, or working on a world record pass.

Imagine skiing while having full confidence with every thought and every movement, at every moment in time knowing, instead of wondering, if you are doing the right thing. GUT is a proactive method of skiing rather than reactive which leads to a learning curve that is shorter, easier, and more fun!

Available to everyone on the soon to be launched Denali Skis website, the next sections of GUT begin to break down slalom skiing into simple easy to understand parts, and explore how this simple objective can be accomplished. The GUT information, being rooted in science, does not change over time, and will only become better understood.  The GUT section of the Denali Skis website is a living document that will be expanded in months and years to come.