Fenix 6s Open Water Swimming under reporting distance & pace

I've upgraded to the Fenix 6s sapphire and the distance (and thus pace) is being under calculated on open water swimming. At first I thought I was just having a slow day or the current was stronger than usual but over multiple attempts I am getting the same result.

I have swam in the same bay for years and from my previous watch, triathlon times and pool pace I know I average between 1:50 and 2:00 per 100m yet on the Garmin 6s it is showing more like 2:30m per 100m.

I wore my friends Fenix 5 on one wrist with the 6 on the other and over a 600m swim the 6s reports 500m. Likewise over an Olympic triathlon distance swim (1800m) the 6s shows closer to 1500m.

I have switched between glonass / galileo and changed GPS to every second to no avail. It seems to be more an error in the distance calculation rather than the GPS tracking as the route shows as accurate when looking at the map post swim. Worth noting distance and pace is accurate for running and cycling.

Has anyone else experienced this?

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0 renton82 over 3 years ago in reply to 5573784

[email protected]

Sometimes they reply sometimes they don't

0 rene.brons over 3 years ago in reply to 5573784

Now you mention this date: did a Fenix6 swim on

Sept 02/2020 in 1:52/100mtr and on

Sept 17/2020 in 2:24/100 mtr.

i have read onthef threads that many people had way to much distance due to an gps error wich is corrected in an firmware update… wich i gues resulted for others (us) in ridiculous, not realistic paces.

0 5573784 over 3 years ago in reply to rene.brons

The thing is that straight line is always the shortest. It is a fundamental law of geometry. Anybody claiming otherwise is mistaken, even if it is Garmin I would accept 2-5% discrepancy, but 20-30% is unacceptable! Please have a look at my screenshots, you will understand better what I am talking about. By the way I performed the same "strait line" check on my last summer swims. The strait line was shorter, as it must.

0 renton82 over 3 years ago in reply to 5573784

You can alway try this "test" https://youtu.be/M88WksWOn1w

0 Olu.F. over 3 years ago in reply to renton82

If you look through this thread, I think I remember reading that the accelerometer helps improve the pace. Where with previous watches I could put the watch in my swim cap for the most accurate readings, this did not work with the Fenix 6.

0 Dr Phil over 3 years ago in reply to 5573784

5573784 said:
The thing is that straight line is always the shortest

Not always...www.scientificamerican.com/.../

0 TeroUru over 3 years ago in reply to bluefish

I am having the issue with my fénix 6. After activity, Garmin connect shows for example 2045m and if I export the activity file as gpx and open it with Garmin connect it shows correct distance as 2560m.

Any idea why this is happening?

0 bluefish over 3 years ago in reply to TeroUru

TeroUru said:
Any idea why this is happening?

Because of the smoothing algorithm in the FIT file.

have already answered that here:

https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-6-series/277028/garmin-connect-open-swim-wrong-distance-correct-distance-when-loading-gpx-file

0 denglerfranz over 3 years ago in reply to TeroUru

Garmin is doing a lot of vodoo with swimming. They do not tell what they exactly do. I try to summarize what I
think they are doing

- GPS is very bad compared to former watches. So often no GPS is obtained. Problem is that watch is only a short time out of water. 910XT was very good (at the price of consuming much more battery)

- So Gramin counts the strokes and uses average stroke length.

- I am not sure if they use the compass. Some swim tracks are against this assumption
However there are tracks they might have use that information

- When they get GPS again they try to correct direction (some linear interpolation or more sophisticated stuff)
and also adapt the average stroke length

- However they to do not make a backward correction. They try to do some tricks and make you faster or slower

The resulting distance during OWS is the mixture of using GPS information, average stroke length, compass (?).
And as my results get better over time I assume that they use history data to become more accurate. A lot of
effort for bad GPS.
I had for example a track where I did a 2700m swim. I mad short pauses at 650, 1300, und 1850. The watch showed
correct 2700m. But the GPS-Track was only 1850. I pressed the stop button to early so that the watch had no chance
to catch GPS again. So if I would do what you did I would get 1850m. However the 2700 are correct.
If you want to see what your watch really recorded export the xy coordinates with https://www.fitfileviewer.com/
and do an xy-Plot with Excel. You will be surprised how bad the GPS performance of the Fenix 6 is.
As I told you the 910XT was much better. And the Fenix 5 worked after three years with several GPS updates.
I updated to the 6X as Dcrainmaker reported the great GPS tracks of the F6.
The response from Garmin is of the kind put your 600bucks watch under your bathing cap. Then GPS is quite good.
However no more strokes and heartrate is recorded then. Sounds don't put any load on your truck then it can climb the hill.
What was interesting that in Triathlon-Mode the swim tracking of the watch seems to be better. However I do not have enough data yet to decide if this results from different settings in the watch or this is just random behaviour.

0 TeroUru over 3 years ago in reply to Olu.F.

You recorded the swim activity as multisport and not OWS which is the mode we are questioning here.