why shorter lines are harder? This is not the answer.

[Horton]

A number of years ago I wrote an article about why shorter lines are harder. The article talked about the angles and the rate of change of angles between the skier and the boat. Lots of math. Bla bla bla

 

I was thinking in the shower this morning and re-framed the whole thing.

 

Here it is: The shorter the rope => the wider on the boat you must be to get around the ball. To get wider you have to travel farther in relation to the pylon. The wider on the boat you must get, the faster you have to go and stay in control.

 

Over simple? Maybe. Helpful information? No.

 

[The_MS]

Brilliant

[6balls]

Because you have to go higher on the boat to get around the buoy thus you are often turning next to the boat, not behind it.

[skiep]

Not to mention if your speed is not correct, turning back to the boat can cause a loose line!

[gregy]

I hope to put your theory to work this summer. Report back when I get there.

[gator1]

Is it April 1 again?

[Razorskier1]

I think it's all a head game. If I can convince myself that 38 and 39 aren't that hard, then I'll run them all the time.

[Horton]

@Razorskier1‌ why stop there. Believe 41 is easy.

[mwetskier]

i do not think there is a single reason it is harder but i do think there is one very important factor. that is the margin of error at 28 off is huge and the margin of error at 41 off is practically non existent. one top skier described the required path for 41 off as ' the width of a garden hose '.

[bishop8950]

Interesting comments above. I know there are governing physics at work, but I think individual perception is also a factor. Here is how I think of it:

 

First, at longer lines we are more behind the boat and at shorter lines next to the boat at the buoy. At long lines we can survive even if we are not free of the boat. To run short lines, you have to be free of the boat (next to the boat) and its harder to get back behind the boat where you want to feel the boat pick you up to accelerate. You are "exposed" longer and the place you need to get to is more specific. So all of your awareness/decisions/movements have to be better to arrive in the place you want the boat to help you accelerate with good body position and a rope that is tight.

 

Second, if you have succeeded in getting behind the boat and are ready to go, yes there is more load at shorter lines. So you have be stronger/better to get side to side at shorter lines

[gator1]

I think it's got something to do with angles and stuff.

[OTF]

@‌horton

"I was thinking in the shower this morning and re-framed the whole thing"

 

If you cut your hair you wouldn't have to use the conditioner, therefore shortening your shower time which would have allowed you to have this thought in another place and leave that statement out...........on the flip side at least we know you want is to believe you shower.

[ForrestGump]

I spent 10 days with JTH on our tour of debauchery. He does in fact shower daily.

[Bruce_Butterfield]

@Horton wow – something simple! Maybe there is hope for you yet!

 

Yes, as the line gets shorter, you have to have more speed and angle. More width will give the skier more speed as long as he holds on to it.

 

I’ll repeat Butterfield’s Second Law: ““There is no such thing as too much speed - only too little control.”

[Porkfight]

Speaking of overhead views...

 

While searching for flag slalom info earlier today, I found this image created by a smart person on the Mastercraft forums. It demonstrates the angles needed for the handle to reach the buoys at varying line lengths.

[gator1]

See. Told you it was angles. I bet I was right, and ther is other stuff too.

[Horton]

You guys see the 2005 version?

 

http://ballofspray.vanillaforums.com/discussion/17/skier-angle-path-2005#latest

 

[Horton]

@Porkfight‌ the graph has to be wrong. At 90° the handle still does not make it at 38 off.

 

if that graph represents a six foot tall skier getting the ski to the buoy I guess it could be right but someone needs to check the math

[Porkfight]

@Horton, it could very well be wrong. He has the buoy out at less than 38' from center at the top of the diagram, making what he said about the handle confusing. It does look like he factored in skier reach, if we ignore his commentary.

 

http://www.mastercraft.com/teamtalk/showthread.php?t=26126&page=2

[doonez]

Perhaps that is meant to be "35 off"? If not, it means he has skipped 35off for some unknown reason (he hasn't missed any other line lengths?)

[skibug]

It is not just about speed and angle; but, where the speed and angle occur that matters...that is where the difficulty lies. This all related to the path the skier takes. I think Jamie Beauchesne once described it in terms of margin of error. He said that the ski path margin of error for 28' off was like skiing on a path as wide as a 2 lane highway, 38' off was like skiing on a path width of a sidewalk, and skiing at 39' off was skiing on a path width of a garden hose.

 

It is easy to philosophize on all of this; but, at the end of the day it comes down to being able to execute. Execution is always the problem.

[klindy]

@Porkfight‌ I'd disagree. The post with the diagram in it says "this is with actual rope length" (I.e. - angle needed to get the handle around the buoy). That being the case I'd say its mislabeled and what's shown as 38 should be 35.

 

There is some commentary which suggests that adding 0 feet at long line and something (5 feet) at the shorter lengths makes sense. I'd agree with that but I think 5 feet is a bit conservative. Should probably be a bit longer

[Horton]

Ok so some guy built a graph wrong or labeled wrong. For once it was not me with the typo. He may be the guy who made the graph in the next post.

[Horton]

[SkiJay]

The graph doesn't need to be accurate to illustrate the concept.

[Horton]

@SkiJay‌ agree but some people believe every thing they read. Next thing you know some guy is at the dock saying he read on BallOfSpray that at 38 off you only need to be at 70.4 degrees to get the handle to the ball. I guess that could be true if the balls are 3 feet narrow.

[jjackkrash]

He probably verified the chart at his home course in Dousman, Wisconsin.

[Horton]

@jjackkrash‌ Oooo lets not go down that ugly rabbit hole.

[Chris Rossi]

I agree with @Horton. Take the buoys out of the equation (it's called free skiing) and you will find that the further out you go, the more difficult it is to make a turn without slack. Then add the lack of space and time to make a turn, and you have the sum of what makes it hard. Keeping it simple is key.

[Porkfight]

My apologies for posting that misleading chart from another forum.

 

Someone mentioned wanting an aerial view and I thought that chart illustrated how the degree of difficulty rises as the rope shortens. Honestly, I didn't really look at the numbers.

[Horton]

Bad! @Porkfight‌ Bad!

 

Who am I kidding your username is @Porkfight‌. You can do no wrong

[Porkfight]

Haha, I try!

[gator1]

It is all about the angles, and some physics, and fluid dynamics.

 

Rope gets shorter, have to get farther up on boat to get to ball.

 

Due to lift/drag (L/D), as we all experienced in a steady state you can't pull up past about 50 degrees on the boat. Just like ice boat can go 65mph and sailboat displacement hull lucky to get 15mph, both sailing across same wind at same angle. Ski has crappy L/D.

 

So to get past 50 degrees up to 90 degrees we have to count more on momentum created by building speed before we get to 50 d. Shorter rope, more speed needed.

 

Unfortunately, water is a fluid and it's drag increase with the square of speed. So, this becomes a self eating water melon. Faster we try to go, the more drag we make.

 

Next, in between the 50d angle, on both sides of the center the arc gets shorter as the line gets shorter, meaning the distance in which we have time to accelerate is less, and therefore the time to accelerate is less.

 

So we're trying to add more speed in less time and we have to use more force to overcome more drag. It's like trying to run a business in the Obama economy. Everything is against you.

 

Then, we have to burn that extra speed off at just the right point in the course, so that we don't coast past the ball when we try to turn, and yet we get to 90 d at the same time as the boat hits the guide balls. Tail riding or smearing or nose riding are all ways to try to brake and burn off extra speed.

 

Next, the turn is more towards the boat so any extra speed gets converted to slack. So again, imprecise speed management get more problematic. The gods turn under the rope so quickly that they convert extra speed into a quicker tight rope. The rest of us just make slack. IMO this is millers secret weapon. He pulls long and gets to the ball too fast, but then turns it so quick that he is back on the rope before the speed burns off.

 

Implications? Go fast faster. Optimize L/d with ski angle of attack. Preserve momentum to ball line. Get slower faster. Turn quicker and through more degrees of rotation without scrubbing speed. Embrace the geek. Sorry @Than_Bogan‌, this thread just kept going.

[gator1]

Shorter rope: more speed for less time and less speed for more time.

[Gloersen]

It's same time for greater distance traveled and it all goes back to desired velocity (speed -direction)

[gator1]

@Gloersen‌ I isually agree with your posts. But I think distance skier travels is less at short line as we ski more point to point. Max speed is certainly higher at short line. But to manage it we have to run slower longer to burn it off.

[gator1]

Ahhh, sorry @Gloersen‌ didn't mean to pile on. Didn't see Chipman's post on the second page while reading on the cell phone.

[mwetskier]

the standard argument is that the skier travels farther along the arc defined by the pylon at center and the handle at the perimeter when the line is shorter. many have disputed david nelsons conclusions.

[Horton]

@scotchipman‌ I do not know if David's theories are correct but I am pretty sure you travel a longer line to run 32 than 22. Making space is drawing a longer path. I really can't make space at 22 but when I crush a 32 or a 35 I have a lot of space. You have to catch up too the boat to run 35, 38 and beyond I do not see how you generate that kind of speed and travel the same path as 22 or 15.

[gator1]

Aw hell. Knew I should have stayed out of this. Even put in a political comment in hopes horton would take my post down.

 

Will you guys accept hard data based on the three guys I ski with, or do I need a bigger sample? And I'm only measuring gate to gate.

[popof]

Hey Guys,

 

Just saw this thread and thought I should share a small calculation I had experimented a couple years ago. PLEASE, axcuse my "scientific english" as I studied in french and therefore might lack some vocabulary. Hope you understand it anyways.

 

As every physical problem I guess you could solve it with the right amount of equations, but as scientists all know that tends to be un-doable in real life given there are so many equations and formulas to take into consideration.

 

So we tend to work with "Models", which are simplifications of the initial problem.

 

My model was pretty much the one described by John and others in this thread, I focused on the MAIN issue beeing the distance the skier has to cover AROUND the boat, or "in reference" to the boat, or I don't know how you should say it in English.

 

Indeed, if you look at it from above, the skier draws the path of a circle (well, a fraction of a circle) around the pylon, so i thought I would just measure the distance the skier has to physically cover, by going from one buoy to the next, at different rope lengths, hoping to find something.

 

I imagined the skier to be standing straight on his legs (obviously wrong) and with the handle perpendicularly above his bindings all the time (again, wrong in real life), and I also imagined the skier would go to the buoy and immediately change directions to the other buoy, as if there was no inertia no nothing.

 

And for rope lengths underneath 38 Off, as we all know, the handle does not reach the buoy, so I said the skier had to "swing" around the handle for a distance that could cover the gap, (basically another fraction of a smaller circle, around the handle this time). (Again, very wrong in real life, but if we take these hypothesis and proceed with a consistant calculus, maybe we will see some trends? At least that's what I was exeprimenting at that time)

 

Well please find attached a screen shot of my Excel file, as you may see, I measured rope length (in M and in ' Off), then the Angle (same as the one described in the picture posted by @Porkfight) in Radians, then the additional distance to actually GET to the buoy when skiing > 38Off, and the distance covered by the skier, in meters (sorry), to physically swing from one given buoy, to the next. (You could then say the slalom consists in 6 times such a swing more or less).

 

I also measured the average speed "around" the boat, or in reference to the boat, meaning that same distance between two buoys divided by the time it took to get there (boat running 34mph, as this is my case).

 

I also measured the incremental change to try to understand why some steps in rope change seem harder then others, as you can see not all "steps" are equally difficult.

 

I hope this makes sense to some of you, and please take into consideration that I just tried this for my personal purpose and do not pretend to hold any greater slalom wisdom or whatsoever, I just thought it fitted the topic ;)

 

Enjoy.

 

Romain.

 

 

[popof]

ps: Forgot the conclusion, ;) , as you may see in the attached file, according to this model, it seems a skier covers more and more distance the shorter the rope, and needs to get to a greater average speed "around" the boat, as the rope shortens, therefore making it more difficult to run shorter ropes ;).

[9400]

It could very easily be put to rest with overhead video analysis...if someone needs to know bad enough.

 

[Horton]

My mathless analysis: At long line I can ski ball to ball with a relatively low average speed and relative to the boat I am always narrow.

 

At 32 or shorter all of the above is not true.

[klindy]

@Horton‌ and since the boat is traveling at a constant speed and the buoys don't change a skier that is traveling faster (at shorter rope lengths) MUST be traveling farther as they round 6 buoys.

[Horton]

@klindy‌ that is what I am saying

@scotchipman‌ we need data acquisition...

[MattP]

@klindy‌ Just thinking out loud here. At 15off you have 22.15' of extra rope if you use all of it would you not have to create extra speed to get back out to 22.15' outside the buoy line?

[klindy]

@scotchipman‌ sorry man you can't convince me that the average speed is slower. You also can't convince me that the average speed is faster! From gate to gate it takes precisely 16.95 (or 16.08) seconds regardless if it's long line or if it's 41 off. So except for some marginal differences at the ends it's the same average speed.

 

The distance traveled is greater as the line gets shorter. Which means the max speed is higher (and the min speed is lower). So the required acceleration and deceleration is greater.

[Horton]

I do not think you guys are looking at the original post do here is what I really think... distance different or not. Maybe I am saying the obvious

 

The difference is your angle on the boat and the rate at which your angle on the boat changes. If you want to touch the ball with the handle at 15 off you need to swing out about 40 degrees from the boat path. At 35 off you need to be 73 degrees from the center line. At 38 off the rope does not reach the ball so I am going to call all passes beyond 35 off as 90 degrees. Of course I realize that most of us do not pass the handle right over the ball. Just go with it.

 

A lot of skiers I know see 32 off as a comfort pass. It is a pass to work on technique. It feels like the harder passes but is pretty forgiving. 35 off is a more serious affair. On the other hand it is only a 1 meter difference in rope length. I think the real difference is that at 32 off you need 62 degrees to get the handle to the ball and at 35 off you need 11 more degrees.

 

At 36mph you have 2.55 seconds and at 34 mph you have 2.68 seconds to get from one ball to the next. These times are absolute. So at 32 off if the handle is going to go to the ball line (11.5 meters) it must be 62 degrees from the centerline and then to make the next ball you have your 2.55 or 2.68 seconds to erase the 62 degrees from one side of the boat and create it on the other side. Back at 15 off you had the same time and the same distance to travel but only the 40 degrees on each side.

 

Part of the difference is that at 15 off you do not have to be beside the boat to get out to 11.5 meters. Speed generation at 15 off is not really an issue. Beyond 28 off there is a need to really generate speed going across so you can coast out and ski parallel to the boat.

 

This does not explain the magnitude of force we feel on our bodies at 38 off. Perhaps it is has to do with centripetal forces or perhaps it is the rapid change in direction that is knocking us out of wack.

 

[gator1]

I read all of Nelson's work Scot posted. Nice analysis, but, as noted by Nelson, limited by the number of data points per ball. A lot of speeding up and slowing down happens in between his three sample points.

 

I'm going to make a big protractor, lay it on the motor box, and video the rope's position as Tim runs 22 up to 38. ZO beep will give me guide ball locations, and I'm going to assume the boat's speed is close enough to 34 mph that it doesn't matter, or at least consistent in its speed variations.

 

Frame rate of the video will give me a time reference. I can then replay the video a frame at a time and get position of the rope vs time, and from that with a little trig I can get velocity and acceleration of the handle in relation to the boat's position in the course.

 

I don't really think distance traveled is important. I believe that there is not much difference in distance between a short line pass and a long line. The different paths Nelson lays out are very close in actual ski distance traveled.

 

I think acceleration rates, max and min velocity, and duration of velocity are drastically different as the line gets shorter, and are required as the rope gets shorter for the reasons I listed above.

 

I know this approach doesn't take into account what happens as Tim disconnects from the rope at the ball, and then gets back on it. If I'm wrong, and I don't see acceleration rates and the rest as a big change as the rope gets shorter, then maybe its all at the ball. But, I don't think so.