Open water swim underestimating distance and lagging

Hi, I also started my open water season and find out that pace is much too low because I think distance is recorded too low.

Recorded this one yesterday along a marked swim course of ~2000m with buoys at ~250m intervals. As much as I'd love to see a faster pace this is my reality. The track is definitely reasonable and the distance pretty close allowing for tide and drift - pace does include a couple of stops too. 

In rebuttal to guy_mx99  I can safely say, and can provide evidence of a summer pf swimming with Garmin watches including the 935 that would suggest he is wrong. Indeed, only today I swam with an F6 on my wrist and a Marq in a swim bag being towed behind in some quite challenging water with this result. The F6 is on my wrist with me swimming freestyle so obviously in and out of the water. The Marq is in a float bag being towed behind so with constant access to GPS. Hard to tell the tracks apart. That to me is quite impressive. Distance by the way is ~1000m as I cut the swim short due to the conditions.

Philip. I don't often contribute to the forum but have been open water swimming mainly in Ireland for years.

I have been using the 935 for two years. I I have logged 48 sea swims this year alone and in the hundreds over the two years with the 935. Therefore I suspect I am quite the expert.

Take a look at the recent screen grab. This is a course with the shore and 3 buoys in a triangle. I did the course 3 times (freestyle) Not very accurate...

Yep have to agree. And to be fair, I too have had some less than average results swimming in small circuits but then others that have been good too. We have a lagoon we swim in occasionally but the course is ˜600m around the three buoys so is bigger than your course. However, as you can see in a straight line with long legs it’s pretty good. 

So a little unfair to suggest everyone avoid Garmin for open water swimming as a blanket statement of fact. What I’d suggest is that people be aware that swimming short courses with multiple turns will possibly to lead to poor outcomes.

I can also find some pretty dismal tracks that have occurred after some software updates too, but in the main, over the years, the tracks have been more often good than bad. This is one of my less than good swims in the lagoon. Granted it's with F6 and F5+ (people seem to think the GPS tracking is worse than the 935) it's sufficient to demonstrate that it's not too bad even in a closed circuit:

I've had over 100 open water swims (maybe 200?) with my 935. Most of the time it's spot on.

I always wait until it connects to satellite before I start (green ring - basic advice). I always enter the water a couple of seconds after I start the swim program so the timer is on and it knows I'm moving before starting my freestyle stroke.

When it has problems it can be because of clouds. It can be because it doesn't properly register a change in direction, particularly when I swim back along a track. It can be because it just doesn't seem to wake up to what I'm doing (sounds like your problem). 

When it doesn't record the track properly it does record time so you can manually enter an estimate of distance based upon your average swim speed.

Hello, I have the EXACT same issue. Open water recording used to be very accurate, but since that FW update the distance is underestimated and lagging a LOT. I see my distance stuct at some previous number and then start to increase super fast to a new distance while i'm not moving anymore. This is very disappointing. Can i roll back to the previous firmware? is garmin working on a fix? 

At the back end of the swimming season up here in the Southern Hemisphere but this is a swim from this morning. The course is a measured 2000m along a buoy line that can be extended by ~500m (the triangle at the RH end). No complaints from this with the latest updates...apart from the average pace but that's because there were a number of breaks. Average swim pace for the 250m swimming laps is Around 2:10/100m.

It's been pretty good throughout the summer.

 Green track is 935 forerunner. Red is a highly accurate BGT31 GPS device in my swim buoy. The screen grab really shows how inaccurate the garmins can be when worn on the wrist. They are OK in a straight line but wildly inaccurate when using a triangular course. Each lap of the triangle is 200m. The 935 measured 25% less on each lap.