gps perfect pass

[sergio moulatlet]

Hi skiers,

I would like to update my PP to a Star Gazer.

What should I do?

Whow will it work , by satelite or by the magnets?

We have one course that loks smaller or shorter once that the PP sugests us to reduce RPMs, how would it work in that case?

 

SM

[Horton]

Are you saying that your course is short? If so then you have bigger issues. 

As I understand it SG uses Magnets to trigger the start of the coarse and then uses GPS from there.

Anyone know better?

[skibug]

The guys at PP are really accomodating and willing to talk to you about their product at length.  I have talk to them a handful of times about technical issues.  They take the time to talk and explain it to you.  I would strongly suggest calling and talking to their technical gurus.

[Chuck_Dickey]

You are right on, John! Trigger at the gates then GPS.  Also will work on a standard mag set up for ABT and GPS controlled the speed.

[Old MS Accout]

I cant wait to get my ZO so I can keep up with all these threads.

[Ed_Obermeier]

As Chuck said, a magnet at the entry gate triggers the timer to start, then GPS measures exactly 259 meters and times that distance.  Period.  Understand that it's not timing the distance of your course from gate to gate, it's only timing a programmed, set distance (259 meters) period.  There is no end-timing trigger point on the course so it's NOT timing the course you're using, it's timing a set distance of 259 meters.

As near as I can determine at this point, there is no way to use GPS speed control to measure your course for accuracy.  The GPS measures 259 meters and tells you how long it took the boat to travel exactly that distance.  True that it starts timing at the entry gate magnet but nothing in connection with the course tells it where to stop timing.  The GPS will give you near perfect times every pass because it's measuring a set distance, NOT your course.  It ASSUMES that your course is dead on accurate, which it may or may not be.  Since nothing connected to the course tells it where to stop timing there is no way to accurately determine if your course is right or not.  If your time is a few hundredths fast or slow it's due to boat speed variables within the given fixed distance of 259 meters, NOT the length of your course. 

If you can look at the end gate buoys as you go by at 55 or 58 kph, listen for the beep to tell you timing has stopped, and determine from that that your course is long, short, or on the money, you have much better eyes than I do.  Other than that I don't see how GPS speed control can be used to determine the accuracy of the course it's being used on.  Someone please enlighten me if I'm off base. 

Ed

[skibug]

How does ZO initiate timing?

[Ed_Obermeier]

You put the boat in the gate and plot a way point into the GPS to tell it where the entry gate is located.  Then when you pass that point as you enter the course the GPS sees the way point location and tells the timer to begin timing.  One of the arguements about ZO is that it's not possible to get as accurate a location for the start-timing point because of the method used (you plot in the way point).  SG gets around that issue by using a magnet to tell the GPS where to start timing, which is likely more accurate.  Don't know that it really makes a difference how it's done, the GPS measures and times 259 meters, NOT your slalom course.  There is no end-timing trigger point on the course so it's NOT timing the course you're using, it's timing a set distance of 259 meters.

Ed 

[sergio moulatlet]

So its a matter of time to have a equipment GPS based to measure the corses or even build them.

How accurate is these GPS based equipment?

Do you think a course can be build only by satelite coordinates?

[Ed_Obermeier]

When EZ-Slalom first went into business Sergio I built a course and  laid it out in a parking lot, measured everything out to make absolutely certain that it was accurate, made whatever adjustments needed made, and started advertising.  I can't imagine that the other guys haven't done pretty much the same thing (I've heard some claims but I won't go there...).  So I tend to believe that the commercially available floating-style courses are probably just fine, certainly I know that ours are.

We recently found out that we've been chosen to provide both the slalom and jump courses for the Junior US Open June 21 - 22 (Cincinatti area) so I'll be doing the same thing againvery soon, we will use a surveyor and the same methodology used at tournaments as these courses MUST survey out to be of record capable accuracy.  So we'll be doubly certain of our accuracy, plus that accuracy will be independently certified by a third party for the tournament.  We've had reports over the years of at least 3 of our courses being used in tournaments (mostly C level) and being certified as being in tolerance.

Commercial GPS surveying equipment isn't accurate enough for that but you don't need it,  todays laser based surveying equipment is plenty sufficient.  One of the cool features of Stargazer is that you have both GPS and old style speed control options.  So it wouldn't take too much doing to find out if in fact your course is in tolerance or not.    Simply run the boat through the course several times in Classic mode and get your times FOR THAT COURSE perfectly on the money.  THEN run some passes with GPS mode and see what the differences are.  You'd have to run several passes with both in calm wind conditions to get a good accurate average I'd think.

For every one one-hundredth of a second traveling at 36 mph (58K) the boat travels 6.34 inches (16.1 cm). The allowable tolerance for the entire length of the slalom course is 0.25 % which comes out to 25.49 inches or 64.74 cm.  It takes 4/100 of a second to travel 25.49" at 36 mph or 58K.  So if the time diference is more than 4/100ths of a second there may well be an issue.  Simple enough to do.

Ed

[sergio moulatlet]

Ed

 Thank you.

You made your point .

 

SM

[Roger]

Isn't the Junior US Open a record capable tournament? For jump, you could use a center line course, but not for slalom.

 From the USA Waterski Technical Controller's Handbook (See item 3):

10.16 Slalom Equipment and Definitions a)

Buoys: For specifications see Rule 8.09.

1) Skier buoys and the end gate buoys shall be bright red or orange.

                    2)

The interior boat guide buoys shall be bright yellow, except that the 55m alignment buoys outside the course on either end shall be of a contrasting color (green is recommended).

3)

For Record Capability tournaments, buoys must either be individually anchored to the bottom or suspended on cross-ways lines anchored on opposite sides of the course. Floating "cable" courses which are anchored solely at the ends of a centerline cable are not permitted for Record Capability tournaments.

 

 

[Horton]

Hey Ed,

I am glad that someone has a handle on it. I just want the season to get here so I can ski.

[Ed_Obermeier]

I'm not sure of AWSA's involvement with this tournament, however I have been told by the folks in charge that this IS an IWSF sanctioned record capable tournament and a centerline course CAN be used as long as it meets certain criteria, one of them being the anchoring issue.   Some modifications to the setup will have to be made but we will be using a stock issue EZ-Slalom SS cable mainline, which WILL have to survey out to be within record capable tolerance.  Not a problem. 

The mainline will be anchored at multiple points, not just solely at the ends, meeting that rquirement.  The skiers turn buoys will be independently surveyed in and anchored so there are no buoy arms alowing the turn balls any movement.  I have had and am in contact with the technical controller for the event and I have the information and specifications necessary to build the courses to record capable specs and tolerances.  So yes, it is a record capable tournament and yes, a centerline-style mainline course can be used and made to meet specifications. 

Ed

[Roger]

"The mainline will be anchored at multiple points, not just solely at the ends, meeting that rquirement."

 That sounds like the key issue to overcome in the rule: "Floating "cable" courses which are anchored solely at the ends of a centerline cable are not permitted for Record Capability tournaments. (which are anchored solely at the ends of a centerline cable)."

The additional steps you're taking sound good also, but that's the one that stands out to me in regards to the AWSA rules.

BTW, I personally had/have no issues with the use of a centerline type course. I responded because I occasionally ski at a site with one and they never have record capable tournaments there. When I asked, the centerline course was given as the reason, so I looked up the rule. Your post simply brought it back to the surface.

Rog

[Ed_Obermeier]

No worries Roger, your question is totally legitimate and rightfully requires clarification.  I raised exactly that issue with the tournament controller (along with several others), we went through it point by point to discuss how all of these issues are dealt with to be certain that in fact I COULD build a course they could use for a record tournament.  It's my understanding that the controller does quite a few tournaments each year and in several countries, not just the US, and has used floating cable courses numerous times.  So he's got all of the attached issues covered. 

Exciting stuf for us and obviously a lot at stake, so I damn sure want to be double certain that it's being done right.  If you or anyone else sees any other issues please raise them so they can be addressed and dealt with.  I only see that as being to my/our benefit.  They should have their event web site up anytime now, as soon as it is I'll post a link. 

Thanks, Ed 

[auskier]

this may be interesting to some if you havnt seen it.

http://au.youtube.com/watch?v=eCwGvEwmdLo