The Definition of Speed

[DW]

@skoot123 - when did you work for CAT? Do you still live in the area or now elsewhere.

 

Another thought I had was to consider using a water tank (as in the ones used for scale marine craft testing) and gather loads and water flow data from a ski in that manner.

[Skoot1123]

@DW - I still work for CAT! Just not in the testing world. I'm in design right now. A water tank might be doable - but tough to get accurately. Hmm......university testing? Probably too expensive.

 

Would be fun to get a bunch of ballers together and get some of this done. Wonder if a ski company would be interested in helping/sponsoring??

[jayski]

I am slightly disheartened that ski companies and national sport organizations haven't embraced the use of technology, they are way behind in comparison to other sports...I fully realize it is a small sport and the cost expenditure may be large to begin with but there are lots of grants and tax incentives available for R&D purposes to offset expenses...in all reality it's going to be guys like you who go out on a limb and show them the benefit of this reasearch...

 

Getting a bunch of ballers together would be great to push this forward and to offset the expenses maybe as a group we could all pitch in to fund this type of project also...can only benefit every last one of us, information and results relayed to those that donate...

[block]

I feel a little different about this. I interpret speed to be the load I feel during the time I am going from buoy to buoy. One could measure load with a load cell over the time it takes to get from a starting rope angle to a finishing rope angle. (buoy /buoy).

When I try a new ski my definition of fast is low load; more load equal slower speed. This feeling may not actually match the skis measured speed.

[Mortyski]

Hi @Skoot1123

 

I don't think an angle measuring device on the rope is easy to do. I looked for one and when I looked I could not find anything that would work so while the comment of just mount an angle device on the rope sounds easy enough I could not find anything to do that...so without the location of the handle (length of rope and angle) will acceleration mean as much?

 

I"m working this system with a very large waterski company and once it is operational I want to put a system in the ski school of my favourite pro skier who also skis for that ski brand... so if there are any computer scientists or programmers out there reading this we have all of the equipment purchased we just need to tie the data acquisition to a computer and record / plot the data trends.

 

my best

Mortyski

[Skoot1123]

@mortyski - I'm actually not thinking of an "angle measurement" device per-say. True, there are position sensor's that could be used (think articulation of a hitch on a machine) but I don't think the response time OR the resolution necessary to capture the change in angle (due to response time). I am thinking of a "beam" that has an electrical bridge on it - that can be used to measure the deflection of the beam, which in turn can be calculated to an angle. Another option would be a position sensor mounted to track the travel of the nylon piece on the rope pylon. I have a couple more options too, but don't want to bore everyone about that. Just a though!

[klindy]

An encoder mounted on top of the pylon (fixed to move with the rope) would work. Problem is with the limited angular movement it would need to be a 5000 pulse per rev resolution which generally have glass disks. It would be sensitive enough but pretty fragile. I'd love to be part of a project like this and have spent a bit I time working through the data and potential results.

[Waternut]

With all the high tech stuff we keep talking about, I'm going to offer a very low budget and low tech option that can potentially measure this illusion of speed and acceleration.

 

First place two pieces of electrical tape on the boat. The first on the back of the boat at the angle the skier would start his pull out. The second somewhere on the side of the boat. I'd recommend using the skier's onside pull for more consistent pull outs and I'd probably make the second mark at or near the same angle required to reach the turn balls with a 15 off rope. Have your skier do a series of 10-15 pull outs. The skiers starts at the first mark and pulls through the second mark without letting up. The observer in the boat can use a stop watch to determine the time between the two marks. The observer (or better yet, pylon mounted camera) will need to sit in the same place for all the pull outs to get the best results.

 

After 10-15 pull outs using this method, you would have a series of times to determine if one ski is faster or realistically accelerates you faster than another. This will also give you good data on whether you are comfortable leaning on that ski with good angle because if you don't trust the ski, you won't lean over as far which will hurt your acceleration.

[mwetskier]

buy 1 of these on ebay http://www.ebay.com/itm/221036618437?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 for 499 buck and tye it to the pilon put the read out on top of the motor box and have a camera right over head that can shoot the read out and rope as it moves back and fourth it will record the angle of rope and pound of pull and you can here the magnet beeps on the video to know were the boat is in the coarse all on 1 video.

[Mortyski]

Hi @mwetskier

 

The tension measuring is the easy one to do and I have a tension device already purchased, but thanks for that suggestion. I also have a magnetic timer so that is done as well. The angle measuring is difficult which is why I opted for a GPS based system to get the absolute skier location and acceleration / speed / deceleration vs time vs tension in the rope as compared to the video. The plan was to actually have a screen chart of the skier location vs time, a chart of the speed vs time, rope tension vs time etc and have them superimposed on a Dartfish video which could have two skiers side by side so you could compare how "we" do it vs the pros. The data would feed across the graph as the skier moves through the course in relationship to the time in the course. You could then go back in the video at any time and see all the data to that point. The deal was of course to have a pro ski all the rope lengths at different speeds to get data sets. We could compare different pros on what they do vs the other pros, how a person changes things for the rope length and how a ski performs ie slow ski vs fast ski.

 

 

 

 

 

 

 

 

[Ham_Wallace]

Seems like there is a relation to Speed in Angle. You can speed a ski up with a shallower fin, but you reach a point that the "down course slide" will slow your progress down. Then again, there is a real difference in "fast" and quick". Fast usually is perceived when proper angle is established. Quick is more like the 1st generation Monza which was amazing, but, had a good case of the "dart-ass". They were great after your initial "turn in" at the gates. The establishment of angle is the real equalizer. The newer rockers and softer fore bodies allow for better rope management. i.e.: tighter lines quicker. (or less slack).