Garmin Activity/Fitness Trackers — Issue With ‘Pool Swim’ vs ‘Open Water Swim’.

by Anura Guruge

Click to ENLARGE.

Click to ENLARGE.

This issue as to the difference between ‘Pool Swim‘ vs. ‘Open Water Swim‘ comes up repeatedly in the context of Garmin activity/fitness trackers/watches such as the Vivoactive 3 and Forerunner 645.

The Vivoactive 3 and Forerunner 645, in particular, do NOT support ‘Open Water Swim’ though they do support ‘Pool Swim’.

This distinction and restriction drives folks nuts, so, I decided to get to the bottom of it.

It has all to do with GPS/Glonass support — or lack thereof IN WATER.

GPS does not work very well when the sensor is submerged in water. THAT IS THE CRUX OF THE ISSUE.

If you just want a GPS distance and track while you swim in open water you could try putting your watch into running mode and having it attached to a swim cap. That is supposed to work.

‘Pool Swim’, by definition, means that GPS is DISABLED. Pool swim data is measured using the ACCELEROMETER. Got that? No GPS … just accelerometer.

So, how do the more expensive watches like the Garmin Forerunner 935 and Fenix 5 support open water swimming? They use the GYROSCOPE.

With the gyroscope you only need occasional GPS fixes. The gyroscopes fills in the gaps between the GPS readings. The Vivoactive 3 does NOT have a gyroscope. Hence why open water swim is not available.

But, alas, a gyroscope alone is also NOT enough. For open water swim you ALSO need a powerful enough CPU to continually calculate the data. Got that?

Hence why open water swim is not supported on the Forerunner 645 though it has a gyroscope. The CPU in it is not as powerful as that in a FR935. Got that.

So, that is the deal.

To get open water swim support you need a gyroscope and a big enough CPU. Without that you only get pool swim which only uses the accelerometer.

You can TRY and use running or pool swim in open water — though the results will be mixed and most likely inaccurate.

So, that is the story. Now you know.

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by Anura Guruge