I use a garmin instinct solar set to "every second". Garmin said my max was 25 knots. I uploaded garmin gpx file to gpsspeedsurfing.com and it said I had a 2 sec max of 27 knots. Is this common and which one do I trust?

sailquik said..
The Garmin GPS device is just not trustworthy.

If you want trustworthy, get something better like the Motion.

Is the garmin misleading the gps-speed site too or just me?

Also try using a Garmin windsurf speed app rather than the boating one you've used here - see thread on Garmin Gpstc datafields which cover the main speed sailing categories.

thedoor said..
Is the garmin misleading the gps-speed site too or just me?

It could be either or both. Send me the track and I'll see if I can tell why there is a discrepancy.

sailquik said..
The Garmin GPS device is just not trustworthy.

If you want trustworthy, get something better like the Motion.

I agree. The Garmin arent really suitable for high accurate 1 second speeds. Whenever I get a new device, I put it on the dash on the van and drive a steady 30mph. The readout on the device always says a steady 27mph, as the speedo in the van over reads by 10%. Have a look at the track in GPS-Results and the 1 second trackpoints vary in speed. The watch display and Garmin website probably interpret the trackpoints to the same tolerance of acceleration, but GPS-Results and GPS Speedsurfing will use different tolerances.
I only use longer time/distances to see how fast I went, a 2 second maximum isnt really an accurate measure of ones speed. 1 lucky gust on a flat bit of water isnt representative of the session.

The issue with the motion its production is someone making them part time, you cant just go down the shop and buy one.

thedoor said..
I use a garmin instinct solar set to "every second". Garmin said my max was 25 knots. I uploaded garmin gpx file to gpsspeedsurfing.com and it said I had a 2 sec max of 27 knots. Is this common and which one do

Don't look at 2 sec max speed, accurate or not it is meaningless. Look at the best 5 x 10"or maybe best 10". That will give you a more honest view of your speed. 2" is just a bit silly. At your speed that is about 20 meters ...

But what I would be worried about are the waves at your spot! Your Garmin shows an elevation loss of 400 feet. That is a VERY BIG SWELL!!!!!!!! Especially for Palo Alto!

I believe this link should take you to the gpx file from Garmin connect. Maybe one of you guys can check it out


drive.google.com/file/d/1fo00JMpvge5NUVRCNuN9NGoTJGOw6-qy/view?usp=drivesdk

I just received the file and ran it in two versions of GPS-Results. They both get the same results as you got from GPS-SS. Of course, this is to be expected because GPS-SS use the program in the website.

But IMHO, the results from the 2 seconds is highly suspect and unreliable. There are huge sawtooth spikes in the speed graph from second to second on many parts of the track.

The best 10 second actually looks quite OK on the graph so it is probably quite representative. Some of the other 10 sec results have the big spikes in them so you 5 x 10 sec is probably less indicative.

Screenshot of sawtooth graph:




I'll email you some more observations after I have gone for a sail.

I have a theory about the difference, it's possible the watch uses doppler data to calculate speed, but that's not included in the GPX file so other software has to use positional data. Positional data is only accurate to 1 to 1.5m
so over short distances, this inaccuracy can have a big effect, could easily explain the 2kt difference, especially with the dodgy looking data.

Edit, just looked at Andrew's graph above, and you can see the distance covered for the 2s reading is 12 and 15 metres, so 1.5m is a significant part of that.

Doppler data doesn't have this accuracy constraint. I'm wondering if the .FIT file has it, that would confirm my theory

I think I can see the same sawtooth on gpsresults with the fit file

I downloaded the latest version of GPS-Results (V6.181) and it reads the fit file just fine, but the results are the same and the Doppler box is greyed out. I think that means there is no Doppler data in the file.

GPS-speed took a look at the files and questioned the accuracy of the Garmin Instinct, lol. They suggested a watch upgrade eg Coros Apex Pro and Vertix

Any others available at REI that I should consider?

www.rei.com/c/gps-sports-watches?ir=category%3Agps-sports-watches&r=category%3Acamping-and-hiking%7Ccamp-electronics%7Cwatches%7Cgps-sports-watches

Open to non REI watches but they have a great 90 day return policy

+1 for what Decrepit says. ^^^^^

If you are not interested in high accuracy or posting in the GPS-Teanchallenge, there are Garmin watches that do a very good feedback job running TBwonders app. The Ones that can handle the app are often on special at a big discount. I understand that the 'Music' models are some of the best for this due to their larger memory capacity. See thread here:


www.seabreeze.com.au/forums/Windsurfing/Gps/Garmin-GPSTC-Datafield-to-complement-the-Motion-Simple-Logger

There is also a poster here (Segler - in the USA) who had had a good experience with a low cost Timex Ironman GPS watch. I can't find the original thread, but if you do a search you will find his comments.