Zero Off Question

[rfa]

My apologies in advance if this has been thoroughly discussed in the past…I did a brief search (non-exhaustive by any stretch) but did not find the “answers”

 

I have skied behind PP for the past 10 years at home (public lake) and behind ZO at tournaments in the recent years. Just got a new (to me) boat with ZO and in the process of mapping our home course coordinates and using it, I have come up with some questions. The brief background is as follows

 

• I have a floating slalom (6-7 years old) course that I cannot survey for accuracy

• I successfully mapped it with my new ZO GPS

• I get 16.93 to 16.95 at 34.2 mph consistently, which suggests that the course is quite accurate regarding its length

• However, I have done several stopwatch tests and I consistently get 17.30 -17.35 sec.

• This means that If the boat is actually going at 34.2 mph then my course is about 17 feet too long

• I called the folks that make the floating course and they tell me “no way” the main line could have stretched 17 feet…

• I have done these runs multiple times , so I am certain about the ZO and stopwatch times

• The ZO folks tell me that it monitors/controls speed very accurately, but “position” less so

 

I also did another test …mapped the course twice; once I pushed the SEL button as soon as the end gate continuous beep started; second time waited for the beep to go on a little bit (probably moved another 8-10ft) before pushing the SEL button. Both approaches were mapped successfully. I get the same exact times (16.93 – 16.95) with both mappings. At the accurate 34.2mph speed, 10 ft would equate to a 0.2 seconds time difference. (e.g. 16.75 – 17.15)

 

Given this experience, I (want to) believe that ZO truly controls boat speed accurately (hence my course is truly about 17 ft too long). If this is true, then the conclusion I have to draw is that the course time numbers we get are “reassuring” in properly surveyed courses but “meaningless” in the sense that it is a “calculated” number based on poor position (or course length) information. In other words, what we get is a display that says 16.95, but should say 34.2mph…

 

The less attractive scenario would be that my course is actually sized properly and the boat is only going at 33.5mph…

 

I assume this has been “put to rest” a long time ago (e.g. they did lots of stopwatch tests on surveyed courses and got 16.95's), but this is my first experience with actually mapping a course and I am curious…

 

Any answers or suggestions on where to find them would be appreciated

 

rfa

 

[thompjs]

Is your course visible on Google Earth? If it is that far off you can tell with the Ruler option.

 

I've used the Ruler on courses I personally set and surveyed and I can get within a few inches of the correct distances between buoys.

[Roger]

When you map the course with ZO GPS, you're only mapping the starting position at each end, not the length. The boat will travel 34.2mph and the system will beep at the position the boat gates "SHOULD" be at. If your course is long, the last beep will be before you exit the course, it has nothing to do with where you told ZO the far set of gates are, it only uses that to start the run...

[rfa]

Thank you both very much!

 

Thompjs - Have not checked google earth...will do.

 

Roger - That's exactly what it does...it beeps before reaching the end gate (sometimes on the return pass it beeps AFTER the entrance gates and then beeps pretty much on top of the exit gates...)...

 

So my "preferred" scenario seems correct; ZO controls speed accurately and my course is too long (d@#%, I should run more bouys...)

 

thanks again!

 

[Roger]

That would be my conclusion also. The system was tested at several surveyed sites while Perfect Pass measured backup time and times were within .01 at each ball everywhere they did the testing.

[jlittle]

What Roger said. ZO is virtual timing. Unlike magnet timing which would be somewhat more "actual" as far as timing goes. That said, and this was beat to death a while ago, ZO runs very accurate speeds. So your boat is going 34.2 (55K).

 

Another thing I've heard about stopwatch timing is it's only reliable to +/- .24 seconds. Or at one time that's what I was told from a track & field runner. My personal opinion is you can get it slightly better when timing your boat but just an FYI.

 

Do you have another boat that has been "timed in" on your course. Meaning, you had, or still have, magnets in the course. You could run your ZO boat against that boat for a side by side comparision. If that's doable and the other boat has PP Classic you'll need it to actually run through the boat gates to get a good comparison. And you along side.

[rfa]

Thanks!

 

With your answers I am confortable that the boat/ZO are OK and I will try to determine the length of the course either through Google earth or side-by-side with a PP boat (yes we still have the magnets in place...)