Towline Tension

[BG1]

So I’m reading here that @MarcusBrown is saying the skier has to learn to control the ski with their body and @adamhcaldwell is saying the skier has to learn to control their relationship to the boat with their body. I’d say you have to do both to ski your best. My question is which has to come first? Is it the chicken or the egg? Is there an answer? I will say this. If you took the 10 best and most knowledgeable minds in slalom skiing and gave them a year to come up with the most accurate skiing theory possible plus a comprehensive tutorial on how to implement this theory most intermediate skiers would still struggle to improve without guidance from someone that understands, cares, and has the ability to explain what you’re doing and how to correct where needed. Coaching slalom skiing is hard. Understanding slalom skiing is hard. Skiing is hard.

[slow]

Where does Nate fit in on these styles. That’s who I want to ski like.

[DW]

The waterski version of this: https://www.nature.com/articles/d41586-018-03793-2#:~:text=Whereas%20Bohr%20proposed%20that%20entities,God%20does%20not%20play%20dice%E2%80%9D.&text=(Einstein%20called%20this%20%E2%80%9Cspooky%20action%20at%20a%20distance%E2%80%9D.)

[Adam Caldwell]

@BG1 - the basics of GUT brakes slalom down into independent kinematic systems.

 

Skier + Ski

Skier/ski + boat

Skier/ski/boat + course.

 

You almost have to understand the last one first, before it will ever make any sense how the first one “should work”.

 

I think lots of “ideas” make sense if you focus on the first without considering the last.

 

I can’t tell you how many bad “habits” and issues disappear when you teach people the later two.

[The_MS]

Understanding it all is easy. Getting the body to make it all happen is the hard part.

[ski6jones]

I had a coach ask me a question about what I wanted to be doing at some point in the course. I fumbled and bumbled my words and couldn't formulate a cogent answer. His comment to me was you should be able to tell me what you're trying to accomplish at every point in the course. Until he said that it never even occurred to me to try. So I went and tried to write it all down. Was that ever enlightening! I had pieces and parts but nothing continuous. I even found some contradictory ideas.

 

That one comment was SO helpful to my understanding, right or wrong, of my skiing.

 

These discussions are even more helpful now that I have an idea what I think I want to achieve everywhere in the course.

[ALPJr]

In my experience skiing with Mike Syderhoud in Shasta in 94 and 95 was integral in the development of the knowledge and skills that I’d developed over the previous few years working with another excellent skiing mind and coach David Spencer. A year later in 96 I resumed working with David and continued to build knowledge and skills. Looking back on that time it seems clear to me now that these excellent coaches were also going through an evolution in their processes as their knowledge grew and they adapted to the impacts on skiers by the changes in equipment. For me these coaches, the changes in equipment and hours and hours of studying the West Coast video led to real breakthroughs for me. Over the past couple years, now 15 to 20 or so years later I’m happy to continue evolving my knowledge and skills, however incrementally, with the latest equipment and the lineage of excellent coaching with Terry Winter aka @twhisper.

[ALPJr]

Two more thoughts... First, what sets these and other great coaches apart is their ability to first understand the athlete’s skills and abilities, and then to have the breadth to develop an individualized program for their success. Second thought, we could use a way off topic button.

[Adam Caldwell]

To get this conversation back on topic.....

 

As controversial as this may sound, maybe the conversation needs to shift to answer the following:

 

How we can use body position to "create more load while feeling lighter on the line".

Last night I was thinking about this and I hate say it but one of my main objectives is to create as much load against the boat as possible during the downswing to center, without necessarily 'feeling it'.

 

1. One the path to CL, get the body into an extended alignment to create tons of leverage potential without collapsing under the load as the boat moves further and further away from you during the downswing to CL (aka, become a longer prybar).

 

2. Manage timing with the boat to ensure the load is building progressively along with swing speed into CL. Ideally, both will peak at CL. (Nearly impossible to do if your timing with boat is wrong - you'll feel the load spike before you actually have attained any swing speed)

 

During these two efforts, its important to control the connection and anchor point to the handle (line tension) in order to transfer that load/energy into rotational acceleration around the pylon. To help facilitate that we want the upper mass leading the feet ever so slightly (normal to the ski) as opposed to the upper mass shifting behind the feet.

 

Here is the video from the Malibu event from the beginning of this thread where my max was 3ball at 38 during a pass that I was completely on top of. Having seen Mapple and CP in person back when they were both running 41s all the time, being light on the line is not at all what we want our goal to be.

 

 

 

 

 

 

 

[AdamCord]

Here's my GUT 101 way of explaining the concept:

 

If you carry a ton of speed into and through the turn you have two options for what happens. You can either run down course as you wait for the boat to pass you in order to keep the line tight, or you can take that speed into the wakes and ski into the rope and a slack line. Usually what happens is some combination of both of these things.

 

Now conversely think of the times when you've been really wide and early into a turn, the line stays tight, the and you're able to finish the turn cleanly in a strong position. How much speed did you have on the back side of the buoy? How much load did you have at hookup? Most likely you were moving pretty slowly, and the load was pretty high. BUT because you were in good position you didn't notice the load, it just felt easy to you.

 

So then what is your goal? To minimize rope load or to be wide and early and run passes easily. I'd argue you can't have both. Of course excessive load is something altogether different, and if you're deep water starting at each buoy as you fall off the tail that's clearly not ideal.

 

When I'm skiing well being "light on the line" never enters my brain. Skiing wide and early does though. Believe it or not I did this last summer while running a pass really wide and early with a tight line-

 

 

 

[dchristman]

@AdamCord is that a protractor triangle you use for a handle guard!?

[Adam Caldwell]

hahah...thats a great idea....LOL

[AdamCord]

@dchristman yeah that’s how I keep all this GUT stuff straight while I’m skiing

[dchristman]

A new Denali accessory. Perfect :)

[BG1]

Well that’s a new angle on safety. Although in this case there’s no handle to worry about.

[Horton]

@AdamCord

As with so many things in this sport a big part of the problem is nomenclature. I believe that in my personal skiing I have to resist the temptation to be excessively heavy on the line. In other words I tend to bury my shoulder and create excess load that only converts boat gas into spray. When I try to be "light one the line" I likely have plenty of load in my hands but resist excess load.

[OscawanaSkier]

I've been thinking about @ski6jones comment yesterday:

 

"you should be able to tell me what you're trying to accomplish at every point in the course".

 

Agreed with @Horton about nomenclature. But I also think one of the things that makes people like me "confused" is lack of context. When we read (or listen, in the case of the many good podcasts) about how a skier thinks/reacts/moves at a particular part of the course, we're often missing how they think/react/move in the previous portion, or what happens to them on the next portion of the course. We all know what happens as point X, effects Y, and then Z. Without that through line, it's sometimes very hard to follow and learn from the experts.

 

I think it would be interesting and very helpful for accomplished skiers like @adamhcaldwell, @MarcusBrown, @Horton, and others to document an entire pass (maybe supported with video?), step by step. It would probably be best to name each section of the pass to keep things consistent (even starting with the "start") , and maybe also predefine terms to help reduce the nomenclature issue (although I do think there's value is saying things differently, as different words "click" with different people)??

 

I'm sure some of this is already available in GUT and FPM, but it could be very helpful to have many examples in one place. Happy to start a different thread to explore this more, but wanted to ask your thoughts in relation to the previous comments in this thread.

[AdamCord]

@Horton yes totally agree about the nomenclature. One person's "Light on the line" is another person's "Heavy on the line", just like one person's "Open to the boat" is another person's "Closed from the boat".

 

I think this is why people need to get into the habit of videoing their sets. Everyone has a high res camera in their pocket and they can either hand the camera to a passenger or download wakeye and buy a camera mount. It's really really easy to record and watch video of our own skiing these days. If you're not doing it you're completely missing the opportunity for self assessment and improvement.

 

You might think you're doing one thing and then see that you're not even close, or even doing the opposite! IMO it's often really hard to tell what we're actually doing in the course while we're skiing, with everything happening so quickly. Get video, watch it after you ski, and make a plan for improvement on the next set.

 

@OscawanaSkier Yes I agree that would be very helpful. I know for a fact that if I did it the video would be looooong. If you haven't seen the GUT gate video I did check it out, it's just the gate pullout and turn in and it's nearly 20 minutes! :#

[Adam Caldwell]

I wrote this at some point and never posted it. Figured it wasn't worth deleting.

 

If we want maximum space & time in front of the next turn ball, we need to minimize the time it takes for us to move through the swing phase. For this to happen there must be load on the line. How much load is a pointless conversation. You could have the perception is there is a TON of load when in reality there really isn't (your body position is far from ideal). Alternatively, you could feel very 'light on the line' but have quite substantial load because of great position and timing.

 

At the end of the day more load does not equate to a faster downswing BUT, less load doesn’t either. How we utilize the “load on the line” will is where the magic is. This is why our body position from the feet to the top of the head - in addition to the skis angle of attack is so so critical.

 

Like @Horton stated, you can either use load convert gas to spray, or use that load to increase your swing speed around the pylon. The big question you have to ask yourself is, are YOU loading the boat -or- is the boat loading YOU?

 

@AdamCord mentioned it earlier, - we think that timing between the skier and the boat is probably the least understood part of this sport. From what I can tell - "timing" will tend to dictate whether or not the line tension you create will work in your favor or work against you, as it is TIMING that is the biggest influencer to body position and ski attitude.

[JackQ]

I have always thought that timing was a very underrated aspect of the sport. For one, it isn’t something you can readily see, like hard turns, pulls, body position. I believe it is one of Nate’s comparative advantages in comparison to some of his peers. One observable attribute of excellent timing, is the lack or minimal adjustments a skier makes in a pass. I certainly feel it when I get it wrong and as the rope gets shorter it is exponentially more critical.

[The_MS]

I don’t look at it as loading the line. I look at as keeping speed under control. Too much speed will kill you. Not going fast enough will kill you. Regulating speed is basically like load control. Keep your max speed to the minimum amount needed and keep your minimum speed to the max amount that you need. That is load control. Don’t overload and get too much speed. Don’t underload and not get enough.

[Skoot1123]

Alright skiers: I have been working on an illustration to help us understand this concept/theory of stack towline tension and efficiency. If this needs a new thread or moved somewhere else let me know.

Illustration:

Some of my ideas and takeaways as I developed this illustration. (Perspective is the skier is at centerline)

The closer/lower you get the pull (connection to the rope) from the boat to your center of mass, the less torque you feel from the boat.

The stack moment is counteracting the torque moment created by the angle of stack.

Assuming you have optimized body alignment this helps move the rope/handle lower on your body. When the handle is on your hips (ie: arms straight) more of the force is transferred to your legs (legs are some of your strongest muscles - so this will make it feel like you aren’t working as hard).

As you move the handle down the pull force passes through the center of mass - lessening the torque moment.

The more efficient your body position (stack), the better your speed/acceleration on the “downswing” into center line.

The speed generated into centerline allows the skier to use that energy to carry them outbound (using the pylon as the pivot point) out towards the buoy.

 

I’d like to make another of these illustrations depicting the path out toward the buoy and do a similar description. Hope this helps.

[tap]

Two quick thoughts.

 

1. I like the figure, I think it’s important, but I also think this is the obvious part of the kinematics and is fairly easy to grasp and understand. The overhead view on the other hand I think is much more interesting particularly as the kinematics play out over time and can better identify effective loading of the line vs just trying to slow the boat down. And then combine the two orthogonal frames of reference for the whole picture.

 

2. Maybe a quick refresher of vector addition is in order.

[Adam Caldwell]

Its not only Freddy anymore! Heres another example where the skier with the highest recorded line tension comes out on top!

 

Chelsea Mills Crush it at the San Gervasio Pro event against some stiff competition AND left with an extra $500 bonus.

 

 

 

[BraceMaker]

@adamhcaldwell not to minimize the value of the force/load on the line but I would be very curious to see this done differently. Perhaps angular acceleration/angular change? Thinking Force*Distance instead of just peak force. You cannot really tell if that 270kgs for instance occurred for 1/1000th of a second or if it was sustained over an arc of 20 degrees of swing.

 

If the force and the angular rate of acceleration were integrated perhaps even including some factor of the static drag or weight of the skier you would have a really cool tool.

 

Either way fun for some skiers to get cash.

 

 

[Adam Caldwell]

@BraceMaker - Its for sure instant peak for fractions of a second -at the moment of hookup where the absolute acceleration rate between skier & boat moving away from each other is at its maximum. The sustained load is roughly less then half of the initial load into and through the wakes.

 

We mapped this with a strain gage instrumented pylon years ago with Tom Pollock. Dual strain gages on the pylon provided all the data you need to calculate load vector and swing rates. I believe there was a thread on this at one point showing the data.

 

Heres a clip of a 38off from back then with that plots line load and rope angle. With this data set you can calculate pretty much any parameter you want. This setup was unable to capture the 'peaks' well because when you ran the DAQ off the laptop computer the sampling rate dropped way down, which is one reason the values are a bit lower then I believe any of us expected. But the wave form is essentially what one would expect.

 

 

[Skoot1123]

@adamhcaldwell - almost looks like the data peaks were “shaved” off from that plot. What sampling rate were you hoping for vs what you ended up with?

[Adam Caldwell]

I dont remember exactly what went down, I just know that the software took a shit when you ran off battery power. The only other slight issue was the strain gages were indirectly connected to pylon so there was some loss there as well as the system was portable. The other issue we had was calibrating at the top of the range that we expected.

 

Point is, the data is "good" just amplitudes on peak force were somewhat low.

[tap]

I’d have to pull the data back up to see exactly what we did. I may have done a simple moving average filter to take some of the chatter out, but to me that plot looks like it could be raw data. We were in a bit of a hurry so I did a very quick force calibration with a scale on the pylon. As Adam stated, it is liable to be off a bit, but should be close. I don’t think Adam needed to put the hammer down until the rope got shorter.

 

The data was generated with two strain gauges at the base of the pylon positioned 90 degrees to each other. At the time I thought this was going to be an elegant solution as the total force vector (magnitude and direction) can be resolved. In practice however, when the rope load got too small the signal to noise ratio dropped off to much to be useful. That is why the angular position data is very choppy at the higher angles, i.e. no rope load to measure and derive the angle from. When Adam was pulling hard on the rope the data was very clean. The peaks of the force curve are not ‘chopped off’, that is actually the most accurate portion of the data as the signal to noise ratio was the highest. The leveling off of the force peaks shows that Adam was sustaining the peak load for a short duration as opposed to just spiking it.

[tap]

We did convert this to angular velocity, which showed what I found to be the most interesting part of the data. I don’t fully understand how he does it, but Adam was able to increase his angular velocity coming off the second wake in a sort of slingshot effect. It was clear and evident in the angular velocity plots. The data from when I was skiing had no evidence of that whatsoever, my angular velocity progressively declined after center. It was cool to see the data clearly show the effects of better technique.

[Kroeks]

That is super interesting! I may have to do figuring on that, but my guess is that even though the radius of the handle path is constant relative to the pylon, it's actually tightening when viewed from a fixed point in space after centerline. Skiers that keep the handle close after centerline are keeping their COM closer to the center of that curve compared to skiers (like me) that get separated. Conservation of angular momentum kicks in and the angular velocity increases, kind of like how a skilled mountain biker can generate extra speed on rollers without pedaling by pumping.