Wobbly tracks on map after Open Water Swim

Thanks for your idea! I assume when you say “GPS soak” you mean activating the swim activity, letting the GPS status turn green and waiting an additional 5 minutes before pressing start?

You have a reasonable theory. You would think that someone doing a competitive triathlon would be standing around in the starting area for a long time which gives the GPS more time to lock more satellites. However in my case, I’m not doing competitive triathlons; my routine between a triathlon and just a normal swim are exactly the same because I am doing them both from my home.

In my case, the length of time between when I activate the GPS and when I press start is probably always at least 6 minutes (the walk to the water alone is 3 minutes plus time to stretch, spit-rinse goggles etc). And my multisport swim activities are no different - I do those swims at the same beach with the same warm up procedure. No waiting around at the “start line” because I’m the only person racing! ;-)

Have you been experiencing this specific issue too? Including the erroneous stroke rate data for the first 12 seconds?

9824633 said:

assume when you say “GPS soak” you mean activating the swim activity, letting the GPS status turn green and waiting an additional 5 minutes before pressing start?

Exactly.

9824633 said:

time between when I activate the GPS and when I press start is probably always at least 6 minutes

I would think that would be enough, but it can't hurt to add 5 extra minutes at the start point of your swim.

9824633 said:

the erroneous stroke rate data for the first 12 seconds?

I can't explain that. In my experience the Fenix 6 is the best watch I have used for detecting stroke rate, but maybe it tries to integrate accurate stroke data with inaccurate pace, and then comes up with this result.

OWS tracks have been a bit of a struggle on my part because I swim breaststroke only, and in the past only raised my arm above water every 50 meters or so to get a GPS fix. Despite that, the Fenix 6 still managed a track with straight lines between these points. The distance would keep adding on for a good 20 seconds, slowly recalculating as long as the watch was above water.

I now use the Fenix 6 with GPS off during OWS, another device on a swim float to record the track, and integrate the two in Runalyze. The second device on the float has to be pretty capable to work at such slow speeds, modern devices (Fenix 5 Plus) do much better than older ones (Fenix 2). Even without GPS, the Fenix 6 usually estimates the swim distance and pace pretty good. But it's cumbersome, and in windy weather and choppy waters the swim float gets thrown around and that still messes up the track. (I'm a recreational 'tour swimmer', just enjoying all the places I can't go to on foot, so I like a good track.)

As an update to this post (Oct 2022), I have not been able to reproduce the issue after 25 swims (coincidentally since my original post it has not occurred even once). It appears “the problem” has gone away as of June 20, 2022! (Knock on wood).

I tried activating the GPS for a full 10 minutes before starting the activity, as user “Data” suggested. I tried this multiple times. It might have worked as the issue did not occur. But I’ve also tried activating the GPS only a few minutes (usually about 4 min) before swimming and again, the issue has not occurred.

There have been software updates for the watch and perhaps one of these addressed the issue. Also, the water over the past months has been warmer (12*C or warmer) so the issue may come back as the ocean cools for the winter. Also, I have changed a few settings to my Open Water Swim app as well as changed third-party apps/watch faces/widgets many times since then so the issue could have been caused by a number of things.

If anyone has similar issues arise with their Open Water Swim app please feel free to let me know, but for the time being, the issue seems fixed.

I did a swim a few days ago and had a correct view, first time I'd ever had it happen and had hoped it was something to so with software updates.

Then today, back to "normal" 

I can't figure it out.

I’m not sure if you’re having the same issues as I was having - my track was much more “wobbly” than yours - so your accuracy issues could be caused by something else. Plus your starting position is way off, which to me is a clue. Let’s give some things a try.

- What watch do you have?
- Can you confirm you are swimming a front crawl?
- What is the water temperature?
- Is it typical that your starting position on the map is so far off your actual position in real life?
- On the map of the “bad” swim, where did you actually start? Was it roughly where you finished (west end of beach)?
- Can you post screenshots of your stroke rate graph and speed/pace graph for both the “good” swim and the “bad” swim?
- How long are you letting the GPS “warm up” before starting the activity? Are you giving it a few minutes to lock on your position before starting the activity?

Depending on your responses, I may have a few ideas for you to try.

Thanks.

I'm on a fenix 6X Sapphire.

Yep, freestyle stroke

Water temp was in the 20's degress celcuis.

The inaccuracy of the first point is inconsistent, though it fine when used in run and ride activities.  Side note, I've changed overnight from GPS + GLONASS to GPS + GALILEO to trail whether the resolution is any better.  For this swim, the start/end and turn points are the beaches on the left and right.

Bad swim 

Good swim

On the GPS soak time, typically I open the activity, let it get the green tick and then "shortly" after that would comment.  "Shortly" for my would be less than 2 minutes.

Having read up a little more last night the soak time may be a root cause.  I also tend to look at the bars changing colour waiting for green, not pointing 6 o'clock points to the sky.

That said, per above, I don't see this issue with run and ride activities and for those, almost as soon as I get the green tick I start, or even sometimes for riding, have already moved off (20 - 200 m) and it "figures it out".

Thanks for the info.

Looking at the stroke rate, everything looks normal. I’m curious about the pace graph but it’s probably normal too.

GPS + GLONASS seems to work best for me. GPS + Galileo didn’t have as good results in my experience but it might just be my geographical location. Or perhaps GLONASS works better for swim specifically. It’s worth a try to experiment.

Yes I would say it would be a good idea to let the GPS soak. Honestly, it doesn’t seem to make a huge difference in my experience, but there is certainly no harm, other than having to plan ahead and turn the GPS on early or delay your swim for a few minutes.

I do think the Open Water Swim app is unique compared to the other apps such as run and bike. Because your wrist is only out of the water for a moment, but does so on a fairly consistent manner, my theory is that the watch is calculating a rough estimation of your route, speed and distance. I find the speed graph shows my speed to be wildly variable, but it simply cannot be in real life as I am swimming in a straight line with a very even stroke. And I find the route on the map is not exactly the route I swim. So I think the watch has an algorithm that estimates your position based on a bunch of inaccurate spot positions that it collects in the 0.5 seconds that your wrist is out of the water, and strings them together the best it can. And that’s how it’s different from run/bike, where the watch can continuously lock your position from multiple satellites. That’s my theory, anyway.

So if you’d like to try a couple of things, here are some suggestions.

One trick that works really well for me is soaking the gps for a few minutes (4-10 min, doesn’t seem to matter for me), wade into the water and submerge the watch for 2 minutes. It will lose the GPS reception of course. After two minutes, bring the watch out of the water and let it regain the GPS signal. Once it turns green, go ahead and press start and begin swimming.

My watch was struggling until I started doing this before each swim. However, the water where I swim is much colder (8-15 degrees C). Cooling down the watch for 2 minutes really helped for some reason. Your water looks lovely and warm so may not change anything for you, but it’s an easy thing to try.

Another thing to try is to press the stop button at about the halfway mark of your swim. Take a short 20 second break with the watch out of the water. Don’t “save” the activity, just stop it. Then after having a short break, press “resume” and complete the swim. Afterward check the map to see if the second half of the swim had better GPS accuracy than the first. It’s not a solution, but if the second half had better accuracy it at least might tell you that something about how you are starting the activity is not ideal - not letting the GPS soak long enough, not letting the watch cool down to the water temperature, starting in a sheltered area where there are too many trees/buildings etc…. It just might provide an indication of something you can change. This is how I discovered that I needed to cool my watch down before swimming - the second half of the swim (the watch was very cold at that point) always had better accuracy than the first half. Pressing stop and resting for a few seconds seemed to give the watch a moment to “catch up” and figure things out.

Lastly, as a final resort, if you can, you could do a factory reset to see if it has anything to do with any of your settings, or third party watch faces, data fields, widgets etc installed on there. I suspect the Open Water Swim app requires a lot of the watch’s processor and memory, so anything installed and running on the watch might cause a problem. But that’s a last resort solution - doing a reset and losing all your settings etc is a big pain.

Good luck! I’m curious if any of these ideas work for you.

Cheers.

Will give the soak and also the 1/2 way rest a try next.