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GUT-102: The Speed and Load Relationship

HortonHorton Posts: 25,665 Administrator
edited February 2016 in Technique & Theory

denaliskis.com


Denali Logo Black.orig

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

Thinking about skiing in terms of extreme limits helps us to understand the underlying physics. Let’s compare two different scenarios at the centerline (CL) of the course to help demonstrate the unique relationship between speed and load.

For the first extreme, imagine approaching the gates, but instead of pulling out to the left, you stay behind the boat and start right on top the left wake. The instant you reach the gates you slam the ski on edge and pull extremely hard to head toward one ball. For this example, let’s assume that you are able to reach 5mph of cross-course speed by the CL, with your ski angle 50° to the course. In a highly loaded position, you are moving much faster straight down the lake (36mph) than across it (5mph).

Now imagine the opposite extreme. Let’s say you are again coming into the gates, but this time you pull out to the left and get very high and wide, nearly passing the windshield on the boat. With a wide and early turn in for the gates you build a lot of speed and angle progressively, allowing you to reach a 40mph cross-course speed by CL, and like the first extreme, with your ski angled 50° to the course. This time you are actually moving faster across course (40mph) than down course (36mph).

Figure 1 illustrates the two extremes we discussed above. As you can see for Scenario 2, the 40mph cross-course speed translates into a 53.8mph resultant speed, while in Scenario 1, the 5mph cross-course speed translates into a resultant speed of only 36.3mph, almost the same as the boat. What’s important to understand is that even though the physical angle of the ski relative to the course is exactly 50° in both cases, the load acting on the ski will be completely different due to the speed and direction of water flow relative to the bottom of the ski.

Figure 1:
Scenario 1: 5mph Cross-course Speed, Ski at 50°



Figure 1:
Scenario 2: 40mph Cross-Course Speed, Ski at 50°


Figure 2 below illustrates how the water flow changes from one scenario to the next as a result of the increased cross-course speed of the ski/skier traveling through CL. In this graphic, the reference has changed to focus strictly on the ski rather than the course and the flow of water relative to it. When the skier has low cross-course speed, the water flows across the ski at a high angle of attack (42° in Scenario 1). However, as cross-course speed increases, the direction of the flow changes significantly even though the ski is still positioned 50° to the course. With the cross-course speed reaching 40mph at CL (Scenario 2), we can calculate that the water flows only 2° relative to the ski - despite the ski’s 50° orientation in the course!

Given this perspective, it is easy to understand why the load is greatly reduced as cross-course speed is increased. The faster you are moving cross-course at CL, the lower the ski’s relative angle of attack with the water and the lower the overall load on the skier. The speed and direction of the water flow across the bottom surface of the ski dictates the magnitude of the lift and drag forces acting on the ski, and consequently how much load the skier must overcome.

Figure 2: Scenario 1: 5mph Cross-course Speed, Ski at 50°


Figure 2: Scenario 2: 40mph Cross-Course Speed, Ski at 50°


Summary
Sustaining speed through the turns and developing high cross-course speed before CL is essential to maximizing your efforts in the pull and successfully running short-line passes. The better you are at generating and managing speed, the less unproductive load you will have, and the shorter line lengths you will be able to run. With a better understanding of the speed/load relationship and the importance of cross-course speed, you can begin to learn more about how to better control your position on the ski to further improve efficiency in the course.

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Comments

  • 6balls6balls Posts: 4,881 ★★★Triple Panda Award Recipient ★★★
    Ok, so light on the line is not all wrong, correct? If done correctly...proper angle with high CL speed load should be lighter and efficiency increased.
    Dave Ross--die cancer die
    AdamCord
  • WishWish Posts: 7,316 ★★★Triple Panda Award Recipient ★★★
    I ski more passes with less effort like never before. Light on the line is a byproduct of the technique.
    >>> 11.25..a different kettle of fish. <<<
    HortonAdamCord
  • HortonHorton Posts: 25,665 Administrator
    @Mark_Matis I think everyone at a high level agrees that you should finished the turn before loading. I do not if future GUT articles will exactly address this but what Chet is saying and what Adam & Adam are saying do not conflict

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  • ozskiozski Posts: 1,566
    Yeah I have to say one should compliment the other when executed correctly.
    'Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.'' Boat 2005 Nautique 196 6L ZO - Ski: KD Platinum

  • Than_BoganThan_Bogan Posts: 6,043 Mega Baller
    This is great! I think you've come to a clearer and simpler explanation of this concept than the early draft that I was priveleged to read.

    Important note to the audience: A lot of the GUT foundation material is really interesting and insightful, but doesn't directly tell you anything to do to ski better. Trust me that that is coming! But Denali feels, and I think they are probably right, that the "what to do" part only really makes sense after you understand some of the science behind it.
    Nathaniel Bogan -- GUT Padawan
    AdamCordWishHortonSkiJay
  • FLeboeufFLeboeuf Posts: 52 Baller
    Are there precise numbers of maximum angle of ski vs water (or amount of lean) that you dont want to exeed depending on how fast you are going throughout the course in order to not overload and obtain maximum speed? Has it been figured out yet or is it not relevant?
  • adamhcaldwelladamhcaldwell Posts: 418 Open or 55K Rated Skier
    @FLeboeuf - We know based on geometry exactly what the minimum cross-course speed is to run the course - based on a straight line path (shortest) distance point to point. We can use that information to then understand what the minimum cross-course speed is at CL. Then, we can use known velocity data captured via radar-gun of the top pros to understand what cross course speed (at CL) it takes to run 41off, and compare that to the known minimum. That means we know the upper and lower limits of cross course speed. The interesting thing is the edge change is dependent primarily cross course speed and ski angle, so we can use resulting velocity data compared against the skis angle of attack to understand the actual edge change, and not only where it can happen, but WHY it happens. This gets very very interesting.....

    All this goes into helping you understand what the challenges and objectives are on the water so you can focus on evolving your confidence, knowledge and technique overcome them.

    The next sections of GUT will get into more and more detail. Stay tuned!
  • adamhcaldwelladamhcaldwell Posts: 418 Open or 55K Rated Skier
    edited February 2016
    @Mark_Matis - The graphics used were to show how much cross-course speed impacts the actual flow of water relative to the skis position. Speeds and ski angle used in the GUT-102 graphic are very possible at 39-41 off @ 36mph.
  • HortonHorton Posts: 25,665 Administrator
    @Mark_Matis Your old HO is like a 1985 Porsche 911 - Cool but WAY outmatched by the current stuff. If you want to divert the conversation off GUT and onto new skis please make a new thread so we can keep this one mostly on topic.

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  • HortonHorton Posts: 25,665 Administrator
    @AdamCord and I have talked about this concept before but when it really clicked is when I related it to jumping. (I was a national competitive jumper in the early 90s)

    When I took ¾ cuts I always had a huge amount more load and less speed than when I took a full double cut. With the full double cuts I was starting my turn at the pylon and making a ton of speed but my loads were too light at the bottom of the ramp.

    Once I moved from doubles to 3/4 cuts my technically best and furthest jumps were from a wide ¾. The guys that were going a lot farther than I was had more of both and were doing it from a full double. They were pros and I was not.

    The first time I tried to transition back from a full double cut to a ¾ I took the worst out the front of my career. The boat seemed to have so much more power and it pulled me right out of position at the bottom of the ramp. At the time I had no idea why. Today it is totally obvious. I had the angle I was used to but a lot less speed so I had much more load than I expected.

    This is not really what this GUT article is about but to me it is a parallel and helps it make sense.

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    adamhcaldwellmmosley899andjulesbishop8950
  • FLeboeufFLeboeuf Posts: 52 Baller
    @adamcaldwell awesome! Waiting enthousiastically and impatientely
    adamhcaldwellsgregg
  • Ed_JohnsonEd_Johnson Posts: 1,848
    edited February 2016
    One of the reasons I loved skiing with Chet was the fact that he would let you know the "WHY."
    If your head didn't explode you would really LEARN a lot.

    What the "ADAMS" are doing here is GREAT STUFF !!! They are really on the right track, and I can't wait for future editions...Thanks Guys !!!!

    Loving the Reflex Supershell with R Style Rear !!!
    FLeboeufski6jonesAdamCordSkiJay
  • FLeboeufFLeboeuf Posts: 52 Baller
    Ed_ johnson, agreed! I also really appreciate the scientific and objective approach to the sport.
  • FLeboeufFLeboeuf Posts: 52 Baller
    @adamcaldwell, just to be sure, "skis angle of attack", is the angle of the ski vs the surface of the water ( or angle of lean if the body is perfectly perpendicular to the width of the ski)? Not ski vs CL, right?
  • adamhcaldwelladamhcaldwell Posts: 418 Open or 55K Rated Skier
    The angle of attack is the ski's angle (or position) relative to the CL of the course.

    What you are referring to is called bank-angle, or roll angle of the ski. For simplicity, in or our discussion of GUT-102, the bank-angle of the ski is not discussed, but is obviously relevant in real-world conditions.
    FLeboeuf
  • AdamCordAdamCord Posts: 600 Open or 55K Rated Skier
    edited February 2016
    @Horton you are on the right track. All things being equal, a 3/4 cut will result in you being slower behind the boat and also having more load on the skis when compared to a properly executed double cut. This is because you are starting with a shorter runway, and thus you have less time and space to build speed. This applies directly to the gate in slalom. A properly executed high/wide gate always beats a narrow one for the same reason.
    HortonMike Gile
  • ALPJrALPJr Posts: 1,624 Crazy Baller
    "A properly executed high/wide gate always beats a narrow one..." simple concept.
  • WishWish Posts: 7,316 ★★★Triple Panda Award Recipient ★★★
    @ALPJr yes but I can be wide/high and slow. I can be narrow and fast and have a better ball one. So a bit more to it then just how high on the boat.
    >>> 11.25..a different kettle of fish. <<<
  • AdamCordAdamCord Posts: 600 Open or 55K Rated Skier
    @Wish it's only timing and body position, how hard could it be?
    Wishski6jones
  • ALPJrALPJr Posts: 1,624 Crazy Baller
    @Wish agreed, much, much more to it. And have enjoyed following the GUT discussions. The quote I wrote from @AdamCord summerized it best for me - the importance or result of the "why".
  • WishWish Posts: 7,316 ★★★Triple Panda Award Recipient ★★★
    @ALPJr haha... ya, completly missread your post and missed that it was a quote. Was to late to edit it by time I realized it. Ooops
    >>> 11.25..a different kettle of fish. <<<
  • Razorskier1Razorskier1 Posts: 3,425 Mega Baller
    This is terrific! @6balls -- one of the concepts you have to wrap your head around is speed, the race to the buoy, and your relationship of acceleration/deceleration relative to the boat.

    For example, last fall I was in the water talking with the Adam's about speed and shortline skiing. In the past I often felt that my problem at shorter lines was too much speed (at the ball). In fact, my problem was too little speed at CL. It takes a lot of speed to catch up to the boat and win the race to the buoy, so you need more speed, but at the right place! Said differently, at CL you will be going very, very fast, and that speed will let you win the race to the buoy. To achieve that you need to be accelerating from turn in to CL. On the other side of the wake (after CL), you will still be much faster than the boat, but will be slowing rather than accelerating. This will (a) give you the feeling of having tons of time at the ball and, (b) will mean that at your desired turn-in point, the boat will be moving away from you, providing you the line support needed to immediately begin accelerating again. When you get this cadence right, it almost feels like you could ski with a blindfold, because the buoys are just exactly in the right place to maintain the rhythm you established with your very first move up on the boat for your gate.
    Jim Ross
    ski6jonesThan_Bogan
  • Razorskier1Razorskier1 Posts: 3,425 Mega Baller
    Oh, in addition, at high speed you can actually pull quite hard without creating load. Pulling hard in the right places creates more speed than load.
    Jim Ross
  • mbabiashmbabiash Posts: 404 Solid Baller
    With all of this in mind. How does zero off letters (A B C) come into play. Should those settings be what feels better to the skier or should we try to ski on a specific letter and change our skiing to a specific letter in order to get max speed at CL.
    I'm not trying to start a zero off thread and it may have nothing to do with this theory but I thought I'd ask.
  • ozskiozski Posts: 1,566
    The answer=A2
    'Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.'' Boat 2005 Nautique 196 6L ZO - Ski: KD Platinum

  • HortonHorton Posts: 25,665 Administrator
    @ozski No. Yes. Maybe. Depends on the boat and the prop & the skier skill level

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  • WishWish Posts: 7,316 ★★★Triple Panda Award Recipient ★★★
    edited February 2016
    @mbabiash so I have not run any letter other then C1 for yrs. Then I got on the Denali and while getting to know the GUT philosophy/science, I started to wonder the same. So for a couple weeks, I ran every letter and every number for multiple passes and sometime revisiting settings just to make sure. I did this without knowing what letter other Denali skiers were using and for the most part had forgotten what the letters and numbers were supposed to do (been on C1 for too long). The letters and numbers were chosen at random..sometimes my driver would just pick for me. So for me, A2 was the letter. Found out later that, and I may be wrong, most Denali skiers are using this same setting. What stayed constant for each test was conditions, site, boat, driver, line length (32) and ski settings. So I ended up ranking the letter and number from most consistent passes to worst.

    A2
    B1
    C2
    B2
    C1
    A1
    A3
    B3
    C3

    What was clear is the 3s seemed to be the worst..brutal actually..C3 about killed me. Letters were somewhat mixed as well as the 1s and 2s. I'm staying with A2. But I think there is room for folks to still find a letter they like. As you get into the nuts and bolts of what you need to do as a skier in terms of the race to the ball, I think it would be very plausible that your preferred letter may change.

    >>> 11.25..a different kettle of fish. <<<
  • Than_BoganThan_Bogan Posts: 6,043 Mega Baller
    Actually @mbabiash, I think that's an insightful question. I've always skied B1, but I found myself liking A2 at least as much when I was really trying to do this stuff (including stuff that hasn't been formally presented yet). Next season, I'll for sure be "starting over" in picking a ZO setting, because the way it interacts with this approach is different.
    Nathaniel Bogan -- GUT Padawan
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