GPS Team Challenge GPS units.

You can join a WA team by contacting one of the team Captains, and getting an invite. If you live south, I would welcome you to the Mandurah Mob. Why wait till 2009, join now? As i've invited you to join the Mandurah Mob, you download a registration form from this site, there is a thread at the top of this section, and fax or email pdf to me. If you live closer to Perth, wait for one of the team captains to inviteyou. If not get a coupla mates together and form your own team, I'll register you and your team, think of a name, and do it now, don't wait!!

I think most people sailing in the challenge are competitive otherwise they would not buy a GPS and compete either against their mates or the big nobs on GPS-SS.
But like Roo says lots of guys just like to strap on the GPS be it whatever make and go for a fang. I hardly ever download my stuff due to different aspects (hope to change soon) but at the end of the day I still want to see if Ive gone faster than the other guys I sail with and against. This is garnering interest from your average back and forth sailor. they probably wont ever get a GPS or compete but its another aspect of windsurfing that holds there interest.
Ive been around windsurfing long enough to have the seen the rise and fall over the years and I sincerely hope we dont go down that path again.
Make it about dollars, high tech or elitism and we will go back down that path.
My 2 bob's worth from a punters perspective.

Some of my team mates are so fast that we would still win if they had egg timers strapped to their arms!

Look I'm 100% behind Garmins being in the challenge. All I'm saying is that since we know they are inaccurate - they give an inflated reading for the two second peak - once we know how much they are inflated by, lets just lop that off the 2 second peak for Garmin users, and then we're all square. If the website can do that automatically, all the better.

I think if the Garmin owners put the display speed down in the 2 sec category things would be OK. The Navi 2 sec and Garmin display are both Doppler readings of 2 seconds duration (Navi) and around 2 seconds (Garmin).
The garmin software 2 second is too unreliable to even be consided by anyone who is interested in what speed they actually achieved (as opposed to getting the highest speed they can vaguely justify).

In all other categories the difference is not significant.

Yes that does make a lot of sense, but at the moment we have a requirement that a file can be produced showing results. But I guess if the file showed a bit over the claimed display speed, that would be OK???
Certainly would then be as close to an even playing field as we are going to get, and no having to stuff around with "fudge factors"

In the 2 and a half years I have had my Garmin I have had no display spikes but quite a few trackpoint spikes... well that was untill I went to distance recording then I got no spikes at all even after a dunking but to stay on 2 seconds when doing 40 I had to put it on 75 feet. Makes the gybes a bit angular so it would hurt the alphas.

A bit more GPS-SS bashing here Roo?
Whilst the GT-11 can be more complicated if you start stuffing around with it, so can the Foretrex.
Your statement about GPS-SS losing participant is mischievous BS! The numbers are increasing at a steady rate and have almost topped 1400. Almost all the new users are equipping themselves with the Navi GT-11.
Sure, some people whinge about how complicated it all is but I seem to remember this in the pre-navi days as well. There are even people out there who can't program a VCR and yet their 8 year old kids can.................
In this sport you can make it as simple or as complicated as you choose.

I think you guys are taking the WA 2 second ranking far to seriously. It has been demonstrated over and over that the 2 sec speeds, even in Doppler are subject to the maximum amount of error. They should only be used for fun as they can't be relied on for any serious rankings.
IMHO, for a top speed ranking you should be looking at at least 6 seconds (roughly 100m) or even better, 10 seconds. At these time intervals the error is decreasing a lot and it should be quite possible to apply a correction factor based on error. That error can be based on theoretical specification values from the manufacturer or on statistical comparisons. Lots of work has been done in this area already because many of the GPS-SS tech group saw this as the fairest way to compare speeds from different GPS types. The downside of this is that the error correction factor for the Garmins works out to be quite large and many Garmin users are upset that they will have what they see as a large handicap imposed on them. I can see their point because a lot of the time the Garmins will give speeds that are not that far out, but then many other times they can be out by quite a lot. Since we have no way of knowing the error of individual session results we must apply the max error correction to all.
Of course, this must be done for the Doppler results from a GT-11 as well but the max error is very much smaller.

A quote from Manfred F uchs' statistical analysis of the error from GT-11(Doppler):

Probability distribution from integration of the measured deviations from 524 500m-runs.



It can be seen from this curve that for example after subtraction of 0.115 knots from the measured Doppler-speed, the true speed was equal or larger than this corrected speed with a probability of 99%.

Here are the figures for Garmin Foretrex (Trackpoint)



It can be seen from this graph that the same 99% probability reliability would require a speed deduction of about 0.725 knots.

Notice that the 90% confidence level is approx. 10 times more error for the Foretrex trackpoints v's the GT-11 Doppler.

Note also that these figures are for the 500m distance. It is my understanding that the error variation is greater for shorter distances/time periods. The correction figures for the 5 x 10 sec are also relatively less than for one 10 sec run.

You miss the point Roo. The maths behind the working of the GPS to produce that simple screen readout are extremely complicated. But no-none needs to worry about it, we simply look at the screen. The Maths/statistics behind a correction factor is the same. The user does not have to know anything about the maths behind it. The analysis program, that everyone uses, does it in the background and you just read off the result. Simple!

When someone wants to know why one GPS is considered more accurate than another we can produce a graph to illustrate/explain. Read it if you like. Ignore it if you like.



Nothing at all wrong with the sceen speed display. It is based on the Doppler calculated speed on all GPS and the speeds from different units are very comparable. There is no 'techies' v's 'majority' divide. All the technically competent sailors I know (which is pretty much every sailor I know) also use the screen speed for 'bragging rights' just as you describe.




Yep, it called a Trimble GPS Survey GPS and is currently accepted by the WSSRC for world record attempts and used by both Macquarie Innovation and Hydropter. Too expensive and a bit too cumbersome for a windsurfer to use easily. Thats why there is so much interest in accurate, low cost personal GPS.



Actually we have that already with the GT-11:

Plug and Play: Check. GT-11's should be (and mostly are) supplied with all the firmware and settings required for speed sailing preloaded (Done with Navilink II at point of purchase). Turn on , select screen display and go.

Big numbers: check.

Large single reset button: nope, done away with the need for re-setting altogether so don't even need that. We have a 'Speed Genie' that gives us all we want to know at the end of each run, not just the max speed but also our 10 sec average speed.

Instant download of results: Check. Well how 'instant' do you need it? Is a simple remove card and read to computer in less than 30 seconds 'instant' enough? It took all sorts of hassle with serial to USB adaptors and unreliable 'cradle' connections and 9 minute download times with the Foretrex. I think we have come a very long way towards 'simple' and 'instant'.

Instant download of results 2: A couple of botton clicks at the end of the session (or during if you wish) recalls your best max speeds and max 10 sec runs on the screen for all to see.



This sounds like a sales pitch. Do I detect some commercial self interest? Are you trying to soften up the market for the next generation of the 'Roo GPS'?



The Aussie Team Challenge is indeed a great success, but a large number of the participants do post on GPS-SS.