Open water swimming

It's hard to say if you can do anything.  Some suggest settings can fix it, I personally believe settings can possibly make a difference but how to see good OWS recording seems more random for my personal device and usage.

Key tips to try:

• Ensure you have a solid GPS connection for 5+ minutes outside of the water before swimming
• Press start with watch out of water and wait a few seconds before starting swimming
• Similarly press stop after standing up with wrist out of water for a few seconds at end
• Ensure your stroke allows your wrist w/ watch to leave the water (!= breaststroke)
• I've seen recommendations that wearing watch on inside of wrist makes things worse, so wear on outside of wrist
• 1 sec recording as a system option is recommended, but know that this doesn't mean it will record a GPS point each second, the OWS mode software still decides when to record points (presumably based on deciding it has a good lock or not)
• Some people say GPS only for satellite is best, others say GPS + Galileo or GPS + GLONASS, I guess try each a few times and decide for yourself if one is best for your usage and area of the Earth.
• Some note using a custom Connect IQ data field with OWS shows poor tracking as well (possibly more points plotted but many inaccurately).

Note, some (many?) argue that the performance got notably worse in the last year or so with a GPS firmware update, but this isn't fully consistent either.  There are at least 2, maybe 3 other threads related though:

1. https://forums.garmin.com/sports-fitness/running-multisport/f/forerunner-935/226350/open-water-swim-activity-not-recording-correctly
2. https://forums.garmin.com/sports-fitness/running-multisport/f/forerunner-935/168047/open-water-swim-issue
3. https://forums.garmin.com/sports-fitness/running-multisport/f/forerunner-935/164647/open-water-malfunction\

It was "top range" back around ~3.5 years ago, it's true that the Apple Watch Series 3 of that era seems to outperform it easily in OWS tracking, however.

I know my wife's Fenix 6s tracks OWS very well (and has a different GPS chipset and SW) and hope the 945 and future watches perform better.

Sorry none of this specifically solves your issue but maybe it provides some shred of helpful information.

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Edit to Add (ETA):

Your best bet (big bummer for a Tri watch, I know) is to place the watch in a floating buoy or in your swim cap in another mode (Walk, SUP, other...?).  You lose the temperature recording and stroke rate, but have a much cleaner (and accurate) measurement of track.

I agree with everything  nord0296 stated. Even if you stop during your swim and tread water, the watch must be kept above water. That said, bc the watch has to interpolate missing data when underwater using an algorithm, even being off +/- 10% is considered good. Mine is usually +/- 5% or so following those suggestions. Best is the buoy or cap solution suggested if you want 100% accuracy.

nord0296 nailed it. 

His answer should be permalinked for all current and future OWS threads.

Great summary, Nord0296!  I relocated to Hawaii during COVID and while swimming in the ocean every day had the opportunity to test lots of scenarios.  Bottom line: 

1) Switch the GPS to 1 sec recording.

2) If you want swimming stats (stroke rate, etc.), use the OWS app and wear the watch on your wrist.

3) If you want an accurate map of your track, use the "Walk" app and strap the watch around your goggle straps on the back of your head.  You can update the activity afterwards on the website to note it was swimming, and will have a very accurate track, which is useful for training for open water races where effective navigation can dramatically improve your results.

Unfortunately, there is no way to get both swimming stats and an accurate GPS track.

Rick said:

Unfortunately, there is no way to get both swimming stats and an accurate GPS track.

I disagree.

The most important thing is a good freestyle swim stroke. I am not fast but swim reasonably well. This is one of any number of swims that I've done with my 935 over the years. It's on my wrist, 1s recording, GPS+GLONASS.

Hey Philips - thanks for joining the conversation. Which part do you disagree with?

Is it the importance of navigation while swimming open water races?  If so, then we will have to agree to disagree, and that topic should probably be discussed elsewhere.

If you disagree that the 935 can provide good swimming stats and accurate GPS track concurrently, then read on.

The main issue is that no watch can get an accurate GPS feed when attached to your wrist while swimming, so the OWS mode INTENTIONALLY smooths out your course into as straight a line as possible.  DC Rainmaker in the first couple minutes of this YouTube video does a good job of describing this issue:  https://www.youtube.com/watch?v=W829SSge2Do&ab_channel=DCRainmaker 

To track his course accurately, DC Rainmaker puts his 935 on a float behind him and DOES NOT use the OWS mode, but rather the RUN mode, which records the actual location without applying algorithms to straighten out the course.  At the end of the video he shows the tracks of his various test swims.  The reference 935 on the float in RUN mode shows a nice clean line of where he actually swam, and the other lines from the watches on his wrists jump around and show where each watch thought he was.  My tests in Hawaii showed similar results.

So if you want to capture all the great swimming stats, then put the 935 on your wrist and use OWS mode.  However, do not be fooled that the nice clean line on the map after is where you actually swam.  If you want to know where you actually swam, especially if there are currents (SF Bay, Hawaii, etc.), then put the watch on your head or a float and use RUN mode (and set the watch to 1s recording w/ GPS+GLONASS).  But unfortunately, you can't get both.

Garmin could solve this problem by offering a GPS receiver that one could attach to the goggle straps on the back of our heads similar to the Finis Hydro Tracker GPS receivers about 15 years ago.  It could sync with the watch before the swim, and download the data after, just like the HRM strap does.  Then the combined system would capture accurate swimming and location information.  Garmin, do you read these forums?

I hope this is helpful to other readers who like me wonder why the watch does not appear to be that accurate while swimming.

Garmin watches, as you quite correctly point out, guesstimate he track from some magic algorithms that they've developed over a number of years since (if memory serves me correctly the FR310XT). Back in the days of the 310XT the tracks were initially pretty garbage but got progressively better clearly identify the path taken. The path the 935 presents is indeed well-smoothed but that is not the same as saying it does not show where you've gone. My regular swim is down a measured buoy line of 2000m, when extended as shown this brings it up to 2500m. For reference the difference between the watches used this morning was around 30m. Newer watches have a much less smoothed track and show similar tracks when compared to a watch in a float bag. 

For comparison. this from a swim this morning with a 935 and F6, one on each wrist, clearly illustrate this:

More examples:

Since this was a 3.3km river swim, it's hard too argue that the track recorded is not the track swum:

I am aware that the screenshots I have posted are mostly not from a 935 but that's because I rarely swim with the 935 except to do a comparison track - see my earlier post with that track.

So, in short, if you have a reasonable swim stroke, the watch can give you a reasonable indication of where you've been and the distance covered when worn on your wrist. If your swim stroke is not conducive to recording a track, or you want a good swim track then by all means put your watch in a float bag or under your swim hat. That's something even Garmin suggest you do - 

https://support.garmin.com/en-AU/?faq=AnrKqtOX8FAzmF9yXaIXe6&productID=702786&searchQuery=open%20water%20swimming&tab=topics

So it is unfair to simply state that the 935 cannot present a good outcome in the open water, it can under the right conditions. I have tracks that clearly show this can be the case as has been shown:

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Are newer devices any better? Depends on whether you like the heavily smoothed track of the 935 or the coarser tracks of the newer watches. Either way, Garmin watches can produce good tracks along with the data you want. It's not black and white.

Rick said:

Garmin, do you read these forums?

If you have a suggestion to make then you need to contact Garmin directly. If you do a search on the interweb you can find the right place to make such a request.

Hi Philips - thanks for sharing these pictures; they are really helpful!  It looks like in each case you have the watches on your wrist in OWS mode; is that right?  Have you ever tried putting one watch on a float or cap in Run mode and the other on your wrist in OWS mode for the same swim? 

Here is an example from DC Rainmaker testing the F5+ (blue) and Polar (red) in OWS mode (blue) using a 935 on a float in Run mode (yellow) as reference:

If you tried that you would see the difference between the guesstimate from OWS mode on your wrist and the accurate track from Run mode on the float or cap.  Then you could decide if that "reasonable indication of where you've been" was good enough given how and where you swim (straight line vs. multi-points, current / no current; enjoyment vs competitive, etc.).

From this morning - 935 in float bag, 935 on right wrist,F6 Solar on left wrist. The interesting thing here is that one of the 935s had a hissy fit with the track but was a reasonable (definitely not the best) indication of the path swum.. The other 935 in the flat bag going for a run was similar to the F6. However, not withstanding the differences in the tracks (which I believe are minima) the distance overall was within 60m, which I think is far more important than the pretty lines on the map.

It is possible that the 935 that went a bit awry this morning did not have up to date satellite ephemeris data (EPO). It was my wife's 935 that has not been used for a while so quite possible. I'll be swimming again on Sunday so will see what both watches are like once I've ensured the EPO data is fully current.

This is what the 935 can produce:

Not withstanding today's swim, I still disagree that:

Rick said:

Unfortunately, there is no way to get both swimming stats and an accurate GPS track.

These tracks are no worse than some of the tracks I get trail running but importantly the pace and distance are correct.

BTW, I found the 5+ to be probably the worst watch to use for open water swimming. I rarely got anything like a decent track or accurately recorded distance. In that case I'd agree that with the 5+ 

Rick said:

there is no way to get both swimming stats and an accurate GPS track.

most of the time.

Hey Philips - thanks for adding these files.  Your experience this morning is pretty consistent with what I am seeing, namely that my 935 on my head is very accurate and on my wrist it is smoothed out by the OWS "guesstimates".  Here are some examples.  All use the 935 with 1s, GPS+GLONASS, current EPO.  The course is the Hilton Hawaiian Village beach in Waikiki which is conveniently exactly 250 yards across.  The swim line is a "dog-leg" to get around the reef you see in the photo.

First run used OWS mode on the wrist.  The lines look pretty and smooth, but I was suspicious as I had to navigate around a couple different groups of snorkelers and that was not shown.  It also only marks a point every 50 - 100 yards:

Next I switched to Walk mode, still on my wrist, and swam the same course.  Walk mode does not eliminate much of the data like OWS, and having the watch on the wrist leads to erratic readings, so the course appears to jump around significantly:

Next I strapped the watch to the back of my cap, still in Walk mode, and did another lap.  You can now see exactly where I swam, including veering too far to the right on the return and having to adjust course.  In a race that could have cost me a couple places, and provided a good training lesson:

So the 935 in OWS mode does create pretty lines, especially if you swim straight courses.  And it captures your stroke and distance fine.  However, if you are swimming unmarked open ocean, dealing with currents, or racing at a level where the straightest course over ground means a difference in your standings, then switching the 935 to Walk mode on your cap gives you meaningfully more accurate track information.  For me that is important, but not for everyone.

The more interesting part of your post was that your F6 Solar did an excellent job of matching the actual track of the reference device.  While I am not thrilled about dropping $800 on a new watch, if the new GPS chipset is that much better, it might be worth it for my needs.  I'll have to do some more research on that.

Thanks again for the information you are sharing.  It is interesting to me and hopefully others.