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  Opinions on which GPS
9/11/2006Scott Alexandwe McCluskey

Hey sorry for asking a dumb question but I am new. I have read the GPS info but would just to check again with anyone who has an opinion, which GPS is recommended any why?
9/11/2006Craig Bergh

Hello,

I think the Garmin Foretrex 201 is a sure bet. It is priced at about $145. It is probably the most generally accepted unit by the speed sailing community. It is small, and precise, and interfaces well with the computer. You should also buy an Aquapac 206 Waterproof case to protect the gps. The gps unit is water resistant, not waterproof.

Email or post here if there are more questions.

Craig Bergh
Worthington, MN
cbergh@iw.net

9/11/2006Andrew Daff

G'day Scott,
Actually, tht is a pretty good question at this time, because the technology of handheld GPS units is starting to move forward a bit about now.
The Foretrex 201 has served to GPS-SS community well for the last coupleof years. The geko 201 likewise. Both have proven to be less than totally waterproof for out use and need protection in an aquapac ot similar.
Technology is marching forwards though and the newer Garmins in the Edge 205 and the Legend CX are noticable better at producing smoother, more precise tracks. They can do so even though they log trackpoints at 1 second intervals. The main problem with the Foretrex 201 and Geko is that they have a built in lack of precision (I call it the grid effect) that puts trackpoints on a 2.4m grid. This causes the graphed speeds to zig zag up and down artificially and is so bad that we are forced to set them to a 2 second interval to try to smooth the track out closer to reality. Up until now we really have not had a viable alternative and since everyone was in the same boat ... ah.... windsurfer maybe...... it hasn't really mattered that much. We now have the choice of some units that eliminate this grid effect and can make tracks that are arguably more accurate and consistent. The Garmin Edge has the added advantage hat it uses the latest Sirf3 chipset which is signifcantly more sensitive to the GPS satellite signal and so should be able to get a better lock on more satellites at all times, thus eliminateing, or at least significantly reducing the errors we call 'spikes' that often cause us so much trouble when editing and validating our tracks and statistics.

The Edge is a bit more expensive than the Foretrex but should perform at a more satifying level. The newer germins mentioned also use direct USB connection to the computers which is much, much, much faster to download. A matter of second compared with minutes for the serial port jobbies. The only practical disadvantage of these units is that you wil only get half the sailing time out of the trackpoint memory because they have the same capacity but save trackpoints every second instead of every 2 second. It still amounts to a couple of hours though and if you have your lapop at the beach it is quick to download via USB and get back to it.

The next step in GPS units is just now becoming apparent and that is the likes of the Navi GPS which combines the advantages listed above with the ability to save the NMEA data to a memory card. The SD memory card can hold a truckload more data than the built in menory of the other units. Days in fact. It also saves a lot of other data about the number of satellites that it is locked onto at any given moment and the reliability or precision of its positional fix, called the HDOP (horizontal dilution of precision). It also save the instantaneous doppler speed calculations, the same speeds that you see in the dislplay as you sail. All this exra data can be used quite easily but software to automatically validate to accuracy of the speeds you record. It can be done in the background without you having to do anything special. It certainly has the ability to simplify the previously 'black art' of track editing and validation and give us much more confidence in the accuracy of our results.

In short, there is no doubt you will be well served with the current generation of GPS unit like the Foretrex and Geko, but I would consider seriously going to one of the newer units if you think you will get a bit more 'serious' about your speedsailing. If you really want to be on the cutting edge, get yourself a Navi GPS and the RealSpeed software (www.intellimass.com/realspeed/single.htm) to analyse the NMEA data. A bit more about it can be found in this thread:
http://www.gps-speedsurfing.com/gps.asp?mnu=forum&smnu=1&val=2562

Some other interesting stuff about gps units can be found in the forum. Maybe start here:

http://www.gps-speedsurfing.com/gps.asp?mnu=forum&smnu=1&val=2342

In if you really want to wade right into it try this thread, but it might be a good idea to pull your gumboots on first! ;-)

http://www.gps-speedsurfing.com/gps.asp?mnu=forum&smnu=1&val=1580

Hope this helps.........
9/11/2006Frank Heinen

I would still advice to consider the trusty Foretrex 101/201 or Geko 201 (al allways to be used in waterproof casing as aquapack or box-it). Some prefer the long lifetime integrated rechargable battery , I personally prefer the aaa batteries of the geko as they are easily changed also on the beach, never miss a session because you forgot to charge...Remeber with geko you have to order a data cable, with foretrex 201 it's included.
Please be aware there is almost none expierence with the new Garmin devices as the Edge, where the Geko and Foretrex are proven technologie. There is still no evidence these devices are really more accurate in practice then the "old" devices with testing side by side (please note we tested with several riders on a certified 500m track the diverences where within 0.1 knots, to put the assumed inaccuraccy of these devices in perspective). Geko and Foretrex can often bought at discount prices, so price difference is pretty big. The new devices can not be used at 1 sec interval, so max recording time is about 3.5 hours where Geko/foretrex can be used for 5.5 hours.
9/12/2006Manfred Fuchs

Hi Scott, if you dont use an equally outdated laptop for the Geko or the Foretrex you have to add the costs of an USB-serial adaptor as well, since the slow serial ports are dying out. The transmission speed (9600 Baud) is 20 trackpoints per sec compared to 500 trackpoints per sec for the newer USB port units. Thus downloading 10.000 points will take more then 8 minutes versus 26 seconds for the 13.000 points a Garmin Edge can store.
The more severe drawback is the limited numerical accuracy of the old devices that some people still ignore or are not able to understand. They transmit only three valid bytes out of the available four bytes leading to the 2.39m grideffect in N-S direction. In E-W direction the gridsize depends on the latitude. At Strandhorst (52 deg) it is 2.39m x cos (Lat) = 1.5m. In diagonal direction the position jumps are even larger (2.8m).
At a measuring interval of 1 second the 2.4m jumps lead to speeds that are a multiples of 8.6km/h = 4.6 knots, at 2 seconds the speeds are multiples of 2.3 knots. That is the reason why the 2 second recordings look so "noisy" especially at slow speeds. 10 second intervals still exhibit a speed resolution of 0.5 knots only. Since the software looks for the five fastest runs (10 sec intervals) this does not really average out, but the fastest outliers are preferred.
The new Edge 205 has a more sensitive GPS-chip and the full numerical resolution (9.3mm instead of 2.39m), so in my opinion the is no alternative if you are interested in your real speed.
9/12/2006Frank Heinen

http://www.gps-speedsurfing.com/gps.asp?mnu=forum&smnu=1&val=2392

As pointed out in this discussion the assumptions of the error calculation on ten seconds avarage by Manfred is not backed up by the practical expierence... May be 2 seconds speeds on the new tools are more accurate but you have to make your own decission if this is worth the extra bucks.

One other thing: 13000 trackpoints at 1 second interval would be downloading 6500 trackpoints on the Foretrex/Geko, so downloading will take not 8 minutes but about 5 minutes for the same amount of sailing time. When you have sailed 5.5 hours with the Geko/foretrex you will need the full 8 minutes Manfred mentioned, but with the Edge you would be missing 2 hours of data....
9/12/2006Manfred Fuchs

I´m sorry to say that again, but the limited spatial resolution of the old Garmins is a fact and leads to the 2.4m grid effect. This leads to a coresponding "speed grid". The stepwidth depends on the evaluation time and the direction of movement. E.g. for Strandhorst in E-W-direction the spatial resolution is 1.5m as stated above, in N-S-direction 2.4m, in the diagonal 2.8m. If you do 2 second interval recordings (try it out when you don´t have enough wind by simply walking around in the different directions) you will thus get discrete speeds with a minimum of 2.77km/h=1,49knots (E-W), i.e. 0, 1.5 (1xE-W), 2.3 (1xN-S), 2.8 (1xN-S, 1xE-W), 2.9 (2xE-W), 3.8 (1xN-S, 2XE-W), 4.5 (3xE-W), 4.6 (2xN-S), 4.9 (2xN-S, 1xE-W), ... knots.
The 10sec evaluations will show the same effect (minimum speed 0.3knots in E-W-direction, etc. - one fifth of the above numbers). With higher speeds the grid effect stays the same, however depending on the direction (the number of steps in travelled in N-S- and E-W-direction) the speed steps may be smaller. E.g. in Namibia where the course is exactly in W-E-direction, one can easily see the speed-grid (spatial grid 2.39m x cos(23deg) = 2.2m -> speed grid= 2.1knots at 2 seconds, 0.43knots at 10sec) in all data I have - one just has to look more thoroughly into the details (zoom in until you see the spatial grid which is the reason for the "speed grid")!
Look at your own data and compare runs in the same direction - the possible distance and thus speed differences can easily be calculated in advance and are very well confirmed by all data measured with the old units - of course most evident in the original 2 sec data steps.
   
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