735XT and Open Water Swimming

Open water swimming is a 'best guess' with any GPS device and very dependent on how you swim. GPS is only tracked when your arm is out of the water between strokes so differences in strokes between individuals will cause differences in position resulting in differences in tracking and distance. The suggested way to overcome this is to put the watch under your swim cap.

Otherwise, you just have to accept there will be differences.

And of course, it's not possible to rule out that you might have a defective device. In which case you might want to see what happens when you record an OWS with the watch under you swim cap.

The biggest factor for the change would be fixing it to your goggles as you would have given it clear access to satellites more often than swimming with it on your wrist. Try it attached to your goggles with smart recording to get a better determination of which is best when the device is attached to your goggles.

I did both and still found 1 second recording and attached to goggles to be more accurate than when on my wrist. Still wasn't perfect though so I'm assuming that would have been the gps chip in the vivoactive? The reason I know it wasn't Perfect as I was swimming in a large strange shaped swimming pool so should have followed the shape of the pool. There were instances where it was off quite a bit.

OK, thanks everyone. I will try the watch in the swim cap trick this next Wednesday when my group gets together to swim.

Relevant tips here.

Just an update. I got a 910XT (cheaply) from another triathlete. I used both watches last night, still on the wrist, just for comparison. I also deleted all of the user data at Garmin Support's request. the results were startling. The 735XT reported 800+ yards per lap, the 910 (on the other wrist) reported 538. Another swimmer with a 735 reported he was getting 750 yards per lap.

Other swimmers with other watches (920, fenix3) were getting ~600 yards per lap. I still have not tried the googles trick, that will be next Wednesday (I missed the last two Wednesdays due to a family emergency and being on call for my job).

Although in the grand scheme of things, the goggles trick (or swim cap) would be one more task for T1 that I don't believe should be warranted. I realize that all of the previous comments in this thread have been that GPS isn't meant to work well while open water swimming, but why are my results so skewed from others that are also swimming with their watches on their wrist? Why would I need to put mine on my goggles, swim cap, or float buoy if others work just fine on their wrist?

Hmm, it is always going to differ for reasons mentioned above. That being said, comparing between wrists can be tricky too as many swimmers have asymmetries, breathing may change how long the breathing side arm is above water, etc. I would put them on the same wrist if that does not interfere with the signal. Or compare each to the other in the cap. But in the end, it is just an estimate since it cannot record under water. The linked tips really help.

Accuracy during openwater swimming with my 735xt seems to improve with Glonass turned on.
I use breatstroke mostly, distancy seems to be similar to what I measure on google earth.



top speed is a 'bit' high though ;)