I went up to Moraine State Park, for another open water swim session this evening.  I was able to get in a decent 30 minute swim, going back and forth just outside the buoy line.

Unlike my swim last Friday morning, this time the water was quite crowded.  This meant I needed to sight about every other stroke, in order to make sure I didn’t crash into anyone.  This was good practice for sighting, but it also meant I struggled to get into a good rhythm.  

I track my open water swims, using my old Garmin 920 XT watch.  I say ‘track’,  but when using a GPS watch for open water swimming, you have to take the data with a huge pinch of salt.  So to answer the question in the title of the blog ….  I have no idea!

When you use a GPS watch in open water swimming, the watch has a very hard time maintaining the GPS signal.  Every time your arm (and watch) goes under water, the watch loses the GPS signal. The watch then has the fraction of time it is above water, to try and recapture the GPS signal, before going under water again.  In reality, it can’t do this well and swim distance accuracy goes completely out the window.

You can see how the watch struggles, if you look closely at the photo.  It looks like I swam in complete zigzags at times during this swim.  I know this did not occur, because I was swimming along the buoy line.  I’m not saying I swam perfectly straight, but I didn’t swim anywhere near the line shown by the watch.

This is why it’s good to swim by time and not swim by distance, in open water.  My coach wanted me to swim for thirty minutes today, and that is exactly what I did.  My watch functions perfectly when it comes to measuring time !!!