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Load and Direction / Pro Ski Coach Water Ski Forum
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#26 Mon, May 11, 2009 4:20 PM

Schnitz
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From: Lake Worth, Florida
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#27 Tue, May 12, 2009 1:39 AM

gregr
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Re: Load and Direction

Schnitz is correct:  acceleration is change in velocity.  If you are skiing directly behind the boat going 36 mph, with your ski pointed at the middle of stern of the boat, you are not accelerating.  If the boat speeds up to 40 mph, you will accelerate along with the boat until you and the boat are going 40 mph, then you will not be accelerating any more.  A change in velocity, or speed, is called acceleration. 

Regardless of the path we take as we ski from buoy to buoy, our direction down the course is a constant 36 (or whatever) mph (other than the minor changes to boat speed as we load the rope and pull against the boat.)  Since we are traveling a much greater distance than the boat as we zig-zag or "S-turn" down the course, we must go faster than the boat speed. 

I believe that we are accelerating from our pull after the buoy up until we begin to initiate our edge change before the next buoy.  Then we slow down (decelerate) probably to some constant speed as we turn around the buoy.

Now what I don't understand is how you get from one bouy to the next without wanting to create as much angle as close to perpendicular to the boat as possible and thus creating as much load as possible in order to create as much angle as possible? 

You don't create load or angle by skiing behind the boat straight down course (other then the load caused by the friction of the ski on the water, the water holding up the ski, and the wind resistance against the skier).  As you ski from one buoy to the next, the more you angle and oppose the boat to get to the next buoy, the more load you have on the rope.  It seems like less angle and less load will cause you to travel down course more and you won't make it to the buoy.

So how do you ski without massive loads and angles?
And, as Schnitz keeps asking, how do you maintain speed in the turn?

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#28 Tue, May 12, 2009 11:31 AM

kstateskier
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From: Southwest Missouri
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Re: Load and Direction

wow - lots of physics talk here...  I never really did that well in physics so let me ask a question.  I'm not really a believer in NOT loading the rope - I kind of like old school slalom.  Recently I've been working on loading the rope later (and by later I mean not so much at the buoy or even at the finish of the turn) but being more patient and Still (upper body still) through my turn attempting to carry as much speed through my turn as possible and "ski my body back to the handle".  Once I've arrived where I feel I should be in relation to the handle I get in as good of a pulling position (stacked position - hands low, knees slightly bent, arms extended) and i'm trying to progressively load the rope into the first wake with all my emphasis on working the hardest right behind the boat and exploding through the second wake to create my width.  Wade/ or anyone else really what are your thoughts on using only the bottom of the pendulum to create my width and speed?  In contrast  find if pull right off the ball through both wakes with the same intensity throughout a few things happen.  One I'm not as connected with the handle in the best body position possible and two I don't carry as much width into the buoy and i decelerate more than i'd prefer, which in turn requires me to accelerate more to stay on tempo in the course.

Thoughts? Comments?  I guess this is just my way of "putting it" without needing a calculator.cool


KstateSkier
"The only thing standing between you and your goals is you"

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#29 Tue, May 12, 2009 1:04 PM

ColinBuchanan
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From: Lake Norman, NC
Registered: Tue, Oct 21, 2008
Posts: 175
Skis At: SkiTek
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Re: Load and Direction

First off if you like to pull realize that the rope will only stretch so much. Once you get to the end of that stretch the rope and boat are going to be pulling you the other way initiating an edge change. If you load the line very hard coming out of a turn then you will get an edge change that is before the wakes and thus not optimizing the best area to use the pull from the boat. Kstate, the fist part of your post sounds like you are working your self towards the right idea but that you might be loading the rope unnecessarily. It is great to have a patient turn that allows you to ski into a tight line with sufficient angle that you will be able to sustain. If you find yourself in that position then you are prime for letting the boat do all of the work for you. Maintain speed through the turn and ski into a good box, arms straight/hips to the handle/trusting balance to rope, and then ride out the pull from the boat until THE BOAT pulls you off your edge through the second wake setting up a wide/early/patient turn that allows you to repeat the above for the other side of the course. I hope this makes some sense without all of the physics talk involved.

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#30 Tue, May 12, 2009 1:54 PM

jbski
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Re: Load and Direction

Colin,
I'm not advocating a hard pull - I'm trying like heck to quit doing that after many, many years of it. But...the boat doesn't necessarily pull you into an edge change. Whether you change edges or not depends on your position on the ski. What happens to a jumper as he or she is trying to get wide on the boat? They maintain a centered, driving position over their skis that keeps them from changing edges at all. They eventually get pulled onto a flat ski(s), but that is not until they are up on the boat. I think the issue of where and when and how you change edges is a great subject for discussion that I'd like to hear from Chris, Wade and others on. Look at Andy Mapple - he is an advocate of a hard pull (load) through the second wake and whitewater that results in a very dynamic edge change. When I watch Terry Winter ski, I see a much earlier forward move of the ski resulting in an earlier edge change, but not as radical as Andy's so his ski carries out great. I would like to hear from the pros what they do to initiate their edge change and where this happens. Personally, I don't feel like I do much of a "move" to make my ski change edges - I just try to keep driving through the second wake. But when I see video of me taken from the boat it looks like I'm pushing my ski through too soon. I think even with a light load there has to be some balance between driving forward for too long (ala a jumper) and pushing the ski through too soon and losing outbound direction.
Jim

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#31 Tue, May 12, 2009 3:01 PM

kstateskier
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Re: Load and Direction

I'm not sure if this has been mentioned yet or not but having watched alot of guys run 38 and 39 and they do it by staying on the handle a long time even after an unload or an edge change.  I think this is KEY when it comes to casting out your ski and keeping width generated from the pull.


KstateSkier
"The only thing standing between you and your goals is you"

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#32 Tue, May 12, 2009 3:29 PM

WadeWilliams
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From: Lynn, MA
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Re: Load and Direction

Not to further detract from this great discussion, but a quick physics lesson (again)

JAS wrote:

The consideration that often gets left out of the discussion is drag. (F=MA +Drag.)

To those of you who think that you levitate on the surface of the water with zero force from the boat when you are skiing directly behind it:

force = mass x accelleration - drag

if force = 0 and mass = 75kg then accelleration = 0

Do you get pulled by the boat or not?

Because if the handle weren't in your hands, you would SINK.


There is negative acceleration that occurs due to FRICTION, i.e., drag.

HENCE the boat offers you a source of positive acceleration, down the lake, all the time that you waterski. When you ski behind the boat you are on the surface of the water due to this positive acceleration that negates the negative acceleration of friction or drag.

Until you let go, then friction / drag overcome your inertia and you sink.



The point is that you can use this constant positive acceleration as your source of speed INSTEAD of excessive load. Because even when you're not loading, you're still accelerating, thanks to the boat.

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#33 Tue, May 12, 2009 4:10 PM

2gofaster
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From: Cypress, Tx
Registered: Sun, Jun 1, 2008
Posts: 337

Re: Load and Direction

I think the confusion, Wade, was that you were talking acceleration relative to a stationary point, and others were talking in relation to the boat. Everything's relative, right? smile


Shane Hill

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#34 Tue, May 12, 2009 4:23 PM

mbabiash
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From: wichita kansas
Registered: Mon, Feb 25, 2008
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Foot Forward: left foot forward

Re: Load and Direction

Wade
Is there any way to obtain a device that records maximum force in lbs. or Newtons that could be attached to the rope.  Compare yours or Rossi's data to an amateur like myself.  This would prove a lot.
This seems very doable.

Matt

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#35 Tue, May 12, 2009 5:55 PM

Thomas Wayne
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Re: Load and Direction

Watch the West Coast Slalom video all the way through and you can see just such a device being used in just such a manner.

TW

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#36 Wed, May 13, 2009 5:04 AM

WadeWilliams
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From: Lynn, MA
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Posts: 1087
Skis At: Not short enough
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Re: Load and Direction

The west coast has a display of the load matched up with the video.

I wouldn't recommend spiking load to 1000 pounds out of the buoy. That sounds like it hurts.


There will be some new technology available at SkiTek in the fall that will clear up a lot of these questions. More information will be made available as we get closer... You will be able to match your stats up against others and learn from there. Should be great.

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#37 Wed, May 13, 2009 5:24 AM

h20dawg79
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Water Ski Sage
From: nashville,tn.
Registered: Fri, Oct 17, 2008
Posts: 562
Skis At: Old Hickory Lake, TN.
Foot Forward: left

Re: Load and Direction

ColinBuchanan wrote:

then ride out the pull from the boat until THE BOAT pulls you off your edge through the second wake setting up a wide/early/patient turn that allows you to repeat the above for the other side of the course. I hope this makes some sense without all of the physics talk involved.

Colin,
I thought your analogy was really very Cool. I had never thought about the Dynamic of Angle VS. Motion and how the Boat boat can and does help initiate a well timed and effecient edge change...smile

This is the stuff great Leverging Techniques are made of...   -"Smarter Not Harder"!


"Warning" -the Surgeon General has determined; That the preceding statements accurately reflect the views and opinions consistent with "DSS" (Delusional Slalomitis Syndrome) a highly contagious life altering condition... (Handle with Extreme care & Patience)

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#38 Wed, May 13, 2009 6:51 AM

Schnitz
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From: Lake Worth, Florida
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Re: Load and Direction

Wade,

It sounds to me like you are assembling the device!  This is something we have been working on for years that will give absolute, definite data throughout the entire course that will show the lines the best skiers are taking through the course, the pressures on the rope associated with these lines and the body positions and techniques used to achieve them.  The British team has been using a device like this for a few years now.  Would anyone like to train with it this summer? 

Schnitz!

Last edited by Schnitz (Wed, May 13, 2009 6:59 AM)

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#39 Wed, May 13, 2009 9:42 AM

kstateskier
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From: Southwest Missouri
Registered: Mon, May 5, 2008
Posts: 76

Re: Load and Direction

Are there waterproof GPS tracking devices you can put on yourself when your skiing and then somehow view the information on your PC to track your path through the course, speed, force, etc? 

Wouldn't it be cool if ZO made a device that you could strap onto your binding or life jacket that sends the skiers info back to the boat that helped the speed control know more about what the skier is doing and in turn give a better pull?  Then maybe the ZO could report the skiers info at the end of every pass...  If the device was somewhere close to the slalom ski itself ZO would be able to judge the pass without even needing a judge in the boat.  Lots of possibilities now that I think about it.


KstateSkier
"The only thing standing between you and your goals is you"

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#40 Wed, May 13, 2009 10:15 AM

jz
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Re: Load and Direction

Didn't Kent over on the water ski forum work on such a device a couple years ago that would capture skier GPS readings, data from a strain guage for line load, boat speed and other data?  Was that what was used in the West Coast vid?

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#41 Wed, May 13, 2009 1:39 PM

h20dawg79
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From: nashville,tn.
Registered: Fri, Oct 17, 2008
Posts: 562
Skis At: Old Hickory Lake, TN.
Foot Forward: left

Re: Load and Direction

kstateskier wrote:

Are there waterproof GPS tracking devices you can put on yourself when your skiing and then somehow view the information on your PC to track your path through the course, speed, force, etc? 

Wouldn't it be cool if ZO made a device that you could strap onto your binding or life jacket that sends the skiers info back to the boat that helped the speed control know more about what the skier is doing and in turn give a better pull?  Then maybe the ZO could report the skiers info at the end of every pass...  If the device was somewhere close to the slalom ski itself ZO would be able to judge the pass without even needing a judge in the boat.  Lots of possibilities now that I think about it.

Check out the "Shadow Box"...http://www.proskicoach.com/forum/viewtopic.php?id=710

This little gadget shows some real promise for the future of many applications.  -Sounds like the Brit.'s already have it figured out though!


"Warning" -the Surgeon General has determined; That the preceding statements accurately reflect the views and opinions consistent with "DSS" (Delusional Slalomitis Syndrome) a highly contagious life altering condition... (Handle with Extreme care & Patience)

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#42 Wed, May 13, 2009 3:30 PM

CBSlalom
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Re: Load and Direction

WadeWilliams wrote:

force = mass x accelleration - drag

if force = 0 and mass = 75kg then accelleration = 0

Do you get pulled by the boat or not?

Because if the handle weren't in your hands, you would SINK.

To clarify the above just a bit...

    The Sum of the Forces = mass x acceleration

Drag (the ski through the water) happens to be one of the forces acting on the body (skier). So... if a skier is skiing directly behind the boat he has at least two forces on him/her. One, the pull of the rope and two, the drag on the ski (one could argue that there is drag on his body moving through the air too). In this case:

     pull of the rope = drag on the ski

Therefore,

   The Sum of the Forces = 0 (zero)

Hence, zero acceleration, but constant velocity even though there is still a pull on the rope.

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#43 Wed, May 13, 2009 3:41 PM

CBSlalom
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Re: Load and Direction

Thomas Wayne wrote:

Watch the West Coast Slalom video

Where do I watch this video. I wanna see it NOW!

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#44 Wed, May 13, 2009 7:13 PM

ScotChipman
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Registered: Wed, May 16, 2007
Posts: 262
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Re: Load and Direction

Link to the West Coast Slalom video www.mikesuyderhoud.com/videos.html


Scot Chipman

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#45 Thu, May 14, 2009 4:23 AM

Schnitz
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From: Lake Worth, Florida
Registered: Thu, Nov 6, 2008
Posts: 118
Foot Forward: Right
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Re: Load and Direction

jz wrote:

Didn't Kent over on the water ski forum work on such a device a couple years ago that would capture skier GPS readings, data from a strain guage for line load, boat speed and other data?  Was that what was used in the West Coast vid?

Yes, Kent never did figure out how to assemble all the pieces so he sent Wade all the parts!  Hopefully Wade can "get er dun" and we can all learn from this tool.  No, this is not the device used in the WC video!

If anyone wants to train with this device NOW, please let either Wade or myself know.  It is very expensive but worth every penny as it will identify exactly what you need to change.  Stop guessing!

Schnitz!

Last edited by Schnitz (Thu, May 14, 2009 4:30 AM)

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#46 Thu, May 14, 2009 5:05 AM

h20dawg79
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Water Ski Sage
From: nashville,tn.
Registered: Fri, Oct 17, 2008
Posts: 562
Skis At: Old Hickory Lake, TN.
Foot Forward: left

Re: Load and Direction

"stop guessing! If anyone wants to train with this device NOW, please let either Wade or myself know.  It is very expensive but worth every penny as it will identify exactly what you need to change." 


I concur.  This device is so sensitive & accurate,  The feed back was exactly what I needed to hear... -it recommended that I take the next 2 weeks off and then quit!  big_smile

Last edited by h20dawg79 (Thu, May 14, 2009 5:08 AM)


"Warning" -the Surgeon General has determined; That the preceding statements accurately reflect the views and opinions consistent with "DSS" (Delusional Slalomitis Syndrome) a highly contagious life altering condition... (Handle with Extreme care & Patience)

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#47 Thu, May 14, 2009 7:41 AM

kstateskier
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From: Southwest Missouri
Registered: Mon, May 5, 2008
Posts: 76

Re: Load and Direction

"and we can all learn from this tool."

No need to call Wade names Schnitz!


KstateSkier
"The only thing standing between you and your goals is you"

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#48 Thu, May 14, 2009 11:02 AM

WadeWilliams
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Pro Skier
From: Lynn, MA
Registered: Tue, May 15, 2007
Posts: 1087
Skis At: Not short enough
Foot Forward: Right
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Re: Load and Direction

Today's physics:

Wikipedia: Friction
http://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Friction_alt.svg/250px-Friction_alt.svg.png

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#49 Thu, May 14, 2009 11:27 AM

CBSlalom
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Re: Load and Direction

Or how about the Bernoulli Principle?

The basis for fluid dynamics and the interaction of our ski and fin with the water.

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#50 Thu, May 14, 2009 12:53 PM

WadeWilliams
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Pro Skier
From: Lynn, MA
Registered: Tue, May 15, 2007
Posts: 1087
Skis At: Not short enough
Foot Forward: Right
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Re: Load and Direction

Good one!!

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