Since the first of this year I’ve done 13 open water lake swims and have tracked them all with my old Garmin Forerunner 305. Sure, there are many newer GPS devices for open water swimming, but the 305 still works well and, if positioned correctly, gives me reliable data. I unintentionally put this to a test on a swim at Parker Canyon Lake on Friday, May 18.
I started the swim after noon, did about a 2 mile route (a little over an hour for me), and then got out to take a break and change from a sleeveless wetsuit to neoprene shorts. According to the marina manager the water temp was 67F, which was comfortable without a wetsuit. I wore the Garmin under my swim cap, something I learned from a 2007 DC Rainmaker post. Usually, I position it where he recommends – on the back of your head – but this time I could feel it more at the top of my head and attempted to adjust it while swimming. When I got out I was surprised to see that I had swum about 3 miles, but I didn’t understand at the time how far off the data was and why. When I resumed the swim after changing (having stopped the device but leaving it powered on), I positioned it at the back of my head.
The data speaks for itself as you can see below. In the first hour, the Garmin is having trouble keeping a signal (I can assure you I wasn’t swimming like that). It appears that I swam about a half mile more than I actually did, and there were a few brief spikes in my speed (15-20 mph) that made it appear as if I was swimming much faster than I typically do. For the second hour, the signal is virtually uninterrupted and more accurately recorded the distance and pace.
My swim looks great on Strava if all you’re looking at is distance and time; but we know the truth!
Winds were gusting up to 18mph for the last mile of my swim!
For another example, check out this video by DC Rainmaker. He did an open water swim test using three GPS devices: a Fenix 3 attached to his swim buoy (which stays out of the water and should be the most accurate), a Fenix 5 on one wrist, and a Suunto Spartan Ultra on his other wrist.
This is an example of a more recent swim I did with a friend who was wearing a TomTom GPS watch. We swam together for the first 2.6 miles and then she headed back to the marina while I completed 4 miles.
