As I worked through the issues and learned the behavior of the F7XSS using both the Pool Swim and Open Water Swim Apps, I started 3 threads in order to share the information and seek advice. Here is what I learned:
1. POOL SWIM: Using the Pool Swim App, I set the pool length and swam one kilometer 13 times in a 50-meter outdoor Olympic pool and several more times in an indoor 50-meter pool. Unlike many of your experiences, my Fenix 7XSS recorded distance every time. My problem was that it was counting extra turns so the distances were way too long. Sometimes it would record 3 or 4 turns on an up and back freestyle swim, thus doubling the distance. I solved the problem and now the Pool Swim App records my swims perfectly. I switched the watch to my right hand. I push off hard and glide on my turns, but I do not do flip turns. I'm sure flip turns would be better, but I do not do them. I touch the wall hard with the watch hand, turn around, push off the wall hard and glide. It counts the turns perfectly and thus nails the distance perfectly. I push the lap button when I want to rest and then hit the lap button again and push off.
2. OPEN WATER SWIM: I ran a thread for a couple of weeks reporting my experience and problems with distance readings using the Open Water App. I was in Mexico and had daily access to a huge resort pool that was as big as three Olympic pools. I could not swim known-distance pool-length laps so I swam around the pool and zig-zagged back and forth across it, swimming what I knew was around 1000 meters. I know my pace well and knew I was swimming somewhere between 1000 and 1100 meters. For ten days in a row the watch reported a distance of about 650 to 680 meters on this 1000-meter swim. This pool was outdoors in open sky, and I had a very strong satellite signal reading.
One poster said that the watch of course loses satellite connection when the arm goes under water and the algorithm predicts your pace based on your previous readings until it gets a signal again. Because the swim legs are relatively short (in this case probably about 60 meters), the watch does not handle this back-and-forth situation well and would perform better on long legs like in an open lake or ocean. Is that true? I think so. Otherwise, the watch and its GPS would be useless for recording open-water swim distances because the watch goes underwater and loses GPS signal.
Yesterday, I ran a test. I returned from Mexico two days ago and went to the outdoor heated50-merter Olympic pool on Fort Sam Houston, San Antonio Texas. I swam a kilometer - 10 times up and back on a 50- meter pool using the open water app and its GPS (not pool length). The watch recorded 700 meters vs the known 1000. Here are some observations I made of the behavior of the GPS recording of distance using the Open Water App.
- I sometimes stopped after a pool length and studied the watch to see what was happening during the swim. I didn't hit the lap button, just let it keep running because I didn't care about the time - just the distance. I observed that the distance kept climbing after a 50-meter length once I stopped and rested at a turn. It would add in another 8 or 10 meters over the next 20 seconds or so and then stop adding distance. I noticed this several times because I would stop after a length and observe the distance reading on the watch. It would keep adding distance while still for 15 or 20 seconds. This is with the watch out of the water while stopped at a turn and a strong GPS signal.
- As a separate test, I swam 100 meters using a kick board and fins. This kept my watch hand out of the water on top of the kick board and pointed towards the sky for the 100 meter up and back. It recorded the 100 meters perfectly to the exact meter (but only after stopping and letting it catch up). I had to pause at the end of the 50-meter pool length and watch the watch distance climb from 38 to 50 meters. Then at the 100-meter mark I watched it climb from about 88 meter up to 100 meters, which was the exact correct distance. Again, the watch seemed to have to catch up after a length of swimming. If I had hit the stop or lap button or just turned and kept swimming, it would have recorded way short.
Again, I'm sure Garmin does not intend for us to use the Open Water Swim app to record distance in a pool. But I did it because I could not swim known distance laps in that big resort pool and I was just using the watch to record a swim that I knew was about 1000 meters in a big pool. Later, I used the open water swim app in the Olympic Pool just to see how the GPS behaved and if it recorded a known distance correctly.
