Where Should The Gates Be?

[Edbrazil]

No firm proposal here; just some more discussion, some math and some ideas for analysis that others might do.

So: If we were able to measure the skier's path during a nice clean pass, and then plunk down

start gates right where they fit the skier's path, where would they be?

 

From observations back-when at some Tour sites that may have had things in the way during

practice/media skiing, such as jump timing buoys, I've noticed that as the towline gets shorter,

the skier crosses the boat wake 'sooner'. Which I remember to be a significant amount, such as

15 or more feet sooner, going from say 28 to 38 off.

 

Suppose you could put the gates at the optimum location, where would they be?

 

From back in the early to mid 1960's, there were some tests and experiments on shortening

the endgates. Which used to be a full 45 yards or 135 feet longitudinally from the # 1 level.

I've heard that Ken White proposed a change, and I remember that such a change was tried

about the 1963 Masters. Also from another oldtimer that there were tests after the 1965 Worlds

in Australia. The top skiers were having to double-turn # 1 at shortline, as in 24 and 30 off.

Of course, all us lesser-talented skiers thought the move was to make the course more difficult.

While the tops guys wanted it.

 

When this idea was incorporated in the AWSA rules, the distance went from 135 to 90 feet.

Note that 90 feet is about 17 inches longer than what we have today at 27 meters. Back at that time,

in the late 1960's, no one was running 38 off. Note that the first US Open Men record recognized

in SL was 1 at 38 at the 1973 Nationals.

 

Anyway, getting back to the original idea, how about using some video from the boat to

determine where the skier crosses the center of the wake? With frame-counting and using

many samples, that should be relatively accurate, especially if there can be good video at a

higher framing rate than the 30-ish fps for NTSC video.

 

Probably Nate Smith would be the prime subject for boat video at super-short line.

Should be plenty of video that @horton and others have. Should be some math/tech geeks

on this site like @than who could put their minds to it.

 

Have a look at the diagrammed example below. Hope it is large & clear enough to be understood.

 

The example is at a line length of 32 off, and where the skier is found to cross the wake in halfway

of the time from buoy-to-buoy (2.545 sec at 58 kph buoy-to-buoy). Turns out that the distance

is close to the 14 meter amount, or 41-27 meters. But, this is just a theoretical example.

 

Since the handle doesn't reach the buoy beyond 35 off (12.00m), what corrections to use for

38 and beyond? Have fun. Could be a good engineering school project?

[thompjs]

@Edbrazil have you read:

 

http://www.schnitzskis.com/davidnelson.html

 

some interesting insight on what you are asking

[A_B]

Drop a few noodles in the water at 27 meters in front of some boat guides and see where your cross the lake in relation to them.

[thompjs]

@AB have you tried this already?

[Edbrazil]

Noodles or whatever for a mini marker that can be seen but is not going to wreck skier.

Such as these small floats about 3-4 inches in size. Maybe could even install a line of them,

in various colors. Even easier than boat video analysis, except for the trip-up factor. Would

be EZ to do at a private site that's relatively shallow and warm now. And, make sure that

the buoy can break away.

 

The link to the extensive data from the Schnitz site is interesting, but flawed. The skier

path isn't such that 1/2 way gate to gate is optimal. Try putting in a marker buoy at 21 feet

closer from the entry gate and see how that works.

[A_B]

No, but I stayed at a Holiday Inn Express.

 

Actually, this was a good discussion and experiment I had with a really good skier from down south, who has put noodles out. He was trying to find the ideal path that could "easily" run 38/39 etc. So he was not using up excess energy and wear and tear on his body. I set up a spreadsheet where we actually timed within hundredths of a second when the skier hit the middle of the wake and added the respective rope length to the position of the boat's distance into the course, giving us the approximate point in the course of the skier. We did this on Regina, Rodgers, .Parrish, etc.... I can dig it up and post if interested. I think I saved it to remote storage before my pc crashed.

 

[thompjs]

Ed, I know it wouldn't work for me! AB, I'll try staying at one before next tournament maybe a WR for me?

 

 

[A_B]

I pulled graph post off. I captured a screen shot from my post on the internet but could not get it to show without the other website. Will try again from a pc. iPad is a little limited.

 

 

[mwetskier]

when the skier is directly behind the boat he will be the line length away and you can measure the time elapsed between the skier rounding the ball and when he crosses the center line by counting individual video frames if you know the frame per second rate of the camera. multiply the speed per second of the boat by the number of elapsed seconds from the ball to the wake crossing and you will know how far down course the skier is when he crosses. or am i missing some thing?

[A_B]

Yes, that is in theory what we did. The other guy has some more sophisticated video playback software with time in fractional seconds and he did the timing and I did the spreadsheet and graphs. I plotted each pass crossing point and put them on a chart so you could compare where the skier was crossing.. Regina's opener, 32 off, was furthest down course, she absolutely smoked 35 off, and that was the earliest crossing point, and 38/39 were in between. I will try to find the spreadsheet and graphs this weekend. I think the 32 was just a warmup and not a high effort level just from watching, and 35 was high effort and the angle obtained was high. I thought if she skied 32 like 35, she could have skied back very early on the crossing.

[RazorRoss3]

I've always found that where they are sets me up 20+ ft early to the one ball so I'd be a fan of right where they are to answer the question posed in the discussion title.

[A_B]

I can't find the spreadsheet, but I snipped the graph I posted before that shows Regina's crossing points. The 32 off is the latest crossing point, and I think she was just cruising and not pushing it. The 35 off was crushed, which is a very early wake crossing point, and then the 38 and 39 are further down course. What I found interesting is even with her very balanced on and offsides, there is still a consistent quicker crossing on her 246 side, her onside..

 

As I said before, I think we started and stopped the timer when the skier was in the middle of the wake. This could be a few feet upcourse from the actual gate, but all passes were done the same.

 

What would be interesting is to have someone try 100% or go all out on longer line passes and see where the wake crossings are at as they go up the rope.

 

[A_B]

If @Mortyski could have got his GPS, Load and Speed tracking system finished, there would have been a great measuring device to see exactly where a skier was at in the course, how much load they were using and where, and how fast they were travelling. Although, while some may think there is value in this, the old analog LISA system that measured the same and estimated position by an angulation measurement superimposed on a graph of where the skier was in theory, just didn't generate much interest, even with Dave Benzel using it at his ski school.

 

Maybe just throwing some noodles in the water would be easier if the question is where does the skier cross the wakes.