By Julie J. -
Currently, Swim.com does not support open water swims recorded by GPS devices (Garmin, Apple Watch 2, etc.). There are several reasons for this.
One reason is that there is a large margin of error possible on results and it could adversely affect the Swim.com leaderboards - one of the main features of our site.
For example, two swims of the same length or course in different bodies of water are not really comparable because of differences in tides, wind, water and air temperature, currents, etc. A person swimming in warmer water with a wetsuit and a tide or current pushing them will swim the same course length a lot faster than someone without a wetsuit in slightly colder water who might be battling a headwind.
Workouts performed by the same person in the same body of water on different dates are also subject to varying tides, wind, water and air temperature, currents, etc., which could provide a slower time result even if you have actually become more fit and are swimming faster and in turn make it harder to see if you are improving. Also, many times two swims of the exact distance in the same body of water will not record the same distance because each time the watch is submerged it loses contact with the satellite and tries to regain each time it is out of the water. There is about a 10% +/- margin of error.
Additionally, when Swim.com first came into existence, open water swim tracking devices made up a very small market share of swim tracking devices. Because of the uncertainty in results recorded and because of the small number of devices in the hands of the public, a decision was made not to accommodate this. This decision could change in the future as devices continue to evolve.
Some watches that Swim.com supports have both an open water and a lap swim mode. Open water swim files from Garmin will be rejected by the Swim.com servers because they are unable to read the data. Likewise, Apple will not allow workout files created by the native apps to transfer to Swim.com. This is why you will not see open water files on Swim.com.
Open water and lap swim tracking modes on watches differ in that GPS records the distance for open water while lap swim distance is collected by utilizing the device's internal accelerometer, a pre-programmed course length, and the motion algorithms programmed within the device's app (whether native or Swim.com).
In order to get an accurate result for lap swimming, the user must program in the correct course length of the pool because the motion pattern generated by a swimmer pushing off the wall with his legs (rapid acceleration after a pause in stroke pattern) during a flip turn or wall push off is what signals to the watch that you have completed a length. In open water swims, that motion pattern is not present and that is why a distance cannot be calculated in this manner and is what makes GPS necessary.