Garmin approved on Gpstc

Sorry, Vosadrian, I just assumed the files were randomly jumbled, but it looks as though they came through in order.

I'm no longer on the advisory group, so my interest is only personal, others will do the real evaluation.

But a quick look, there is good conformity with the motion, (the OAO files are what's wanted, GPX doesn't include some of the data that's needed).

The positional data also looks OK, that's the dotted line, red is the watch blue the motion.

Could be I just selected a good bit, others will be more thorougher.

Probably opening a big can of worms but since a few have asked about Apple Watch on this thread and in the spirit of inclusivity thought I would share my findings after owning an Apple Watch Ultra 2 for the last couple of months.

In summary, in my understanding of this thread, results within +/- 0.2 kts are acceptable for GPSTC. Over the last 3 months I've done 2320km during 75 windsurf sessions in various conditions and locations. Data below. With the exception of 2sec data the rest of the categories from Apple Watch match very well, "almost" always <0.1kt, errors bigger than that are typically a penalty for the Apple Watch, or they are non competitive outliers..i.e. a NM with 4 gybes. The 2 sec data is as expected very unreliable because of 1 sec sampling with typical errors +/-0.7-1kt.

I purchased the watch 100% for communication and health aspects, not for any speed recording. I use 2 approved boom mounted units to log windsurf sessions for GPSTC. When I saw this thread I thought it would be interesting exercise to compare the new watch data with boom mounted units.

First point worth noting is that unlike Michael George who used the Waterspeed app to record sessions, I use the native Apple Activity app and record the session as a cycle ride. After the session the watch ports it to the iPhone and then I use the Healthfit app to auto sync it to Strava where you can download the GPS file. You can record session as a walk or run but then Strava flags it as dodgy due to the speeds so the cycle ride seems to be the best option to record natively on Apple Watch until such time Apple has a native windsurf option.
I haven't seen the watch lagging with initial acceleration like Michael did so suspect the 3rd party Waterspeed app is not getting the data from Apple Watch efficiently? The data seems to track very well with the boom units with no lag. In gybes the sail flip/hand movement nearly always generate something like the below comparison. Comparing two boom units shows similar and been discussed on the DIY GPS thread/YT so seems it is a reasonable artefact of hand movement that doesn't affect #'s in anyway.




For comparison I used GPSSpeed reader with default settings. I've only used one boom unit for the data comparison (as I only have historical files for one boom unit since this thread started) and not the average of 2 boom units. The boom units are always within +/-0.1kt for 2sec and 0.02kt for other categories.

The 2 sec as mentioned is problematic, not as bad as previous Apple Watches though. (Positive difference means Apple Watch reading higher than Boom unit). If you subtract 1kt in all cases you should have honest speed. The observation for me is multiple walking speed tests (not shown here) show +/- 1 kt difference in 2sec or nearly 40% error but above 30kts the error reduces to +/-0.4kts or around 1%....makes total sense for positional only speed...putting it out there before doing any comparisons, for the top 50kt sailors, the error may??? reduce to acceptable limits. The rest of us mortals it doesn't matter.





The 5x10 is much better with the results usually penalising the watch. There are three outlier sessions which are above +0.2kts and two of those sessions show glitches on the Apple Watch that I can't explain. The glitches seem to occur randomly and don't seem to be in the 5x10 calcs.





these the weird random glitches for the outliers for 5x10 but no glitches occur in the calcs..I've found glitches like this in 3 of the 75 sessions. They always have a spike then flatline. No clue at this stage why.




Alpha as expected almost always penalises the watch.




NM always very good with the outliers +/- being non competitive like having 4 gybes




Distance and hr are always slightly +ve due to the 1 sec location only sampling. The distance displayed on the watch in realtime is always different to what is ported to the iPhone. Seems there is some fancy filtering based on accelerometer data etc but in general distance recorded is close but always above. The crazy +ve outlier distance data is when I'm walking about (especially drone sessions) and the -ve data when Apple Watch went flat as I forgot to charge it sufficiently for session.









In conclusion I was quite surprised how accurate the results were and my take is other than the 2sec and a couple of undiagnosed glitches, results from Apple Watch Ultra 2 are on par with the Garmin's discussed here. Seems the data is a solid backup if nothing else. If Apple just did higher sampling might be another option for approved unit. For the masses though the results are pretty good for weekend warrior/no one really cares comparisons. All the raw data shown here publicly available on KA72/Strava or can send if anyone wants to check my results.

Select to expand quote

tbwonder said..

No, they are not close to being on par.
I have produced a graph of 80 sessions of my Garmin 255 vs a Mini Motion. I have set the scales to match your graph above.

You right TB wonder, the 2sec from Apple Watch aren't accurate and will never be due to the 1 sec sampling. Whilst the 2 sec is not on par, the error seems to be almost always less than a knot. So you could just subtract 1kt at all times to have a reasonable idea without being unfair to other sailors.The point I was trying to make is the other categories appear 'on par' with the Garmin with a roughly +/- 0.1kt difference (bigger errors as mentioned are either lower or non competitive). Since the consensus seems to be a 0.2kt error is acceptable for GPSTC and most recreational sailors it seems the data should be at least considered to widen the appeal of GPSTC to a wider user base. The Ultra 3 is rumoured coming around Sept '25 is supposed to have blood pressure, satellite comms and hopefully better GPS. I for one will trade my current watch in for that and do another data comparison.

Thanks for sharing Flex2.

A friend sent the Apple Watch Ultra data to me and asked what I thought. Rather than respond to one person, I uploaded those findings but I've not really looked any more closely because COROS and Garmin have taken up all of my spare time.

The OS provides location data (including speed, etc) via a common class, so it's unlikely that Waterspeed is breaking things imho. I'd also imagine that Apple implement bespoke sport profiles in much the same way as Garmin, COROS and other watches.

With regards 2s speeds, your stats show what would be considered outliers in the Garmin data are occurring regularly on the Ultra 2. There are also some differences which far exceed anything that I've observed on my FR 255 or Fenix 7 Pro.

Can you perhaps upload your data to Google Drive (or similar) so that anyone curious can have a closer look?

K888, trying to upload all the data but something funky going on with google drive today..can't upload a single byte.. will try tomorrow