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I don't know if I'm moving in a marginal zone for smart watches...

My smart watch (Garmin Fenix) has an app for tracking open water swimming. However, I'm swimming breastroke with head-over-water. The arms are likely to be fully under water the whole time. In that setup, even if the hand is a few cm under the water surface, the GPS tracking doesn't work at all! I've learned to make my technique even more amateur by adapting hand movements so that they emerge in straightening phase. It is enough to keep the watch tracking my activity, but I observe strange zig-zags on the activity map, and the distance is a bit longer as I'd expect, so I don't get reliable tracking.

Is it a software problem (assuming everyone swims crawl) or a hardware barrier (you can't get GPS signal 1 cm under water)? Is there an alternative device for open water swimming tracking?

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It’s GPS. A proper breaststroke should have the same type of “catch” as a freestyle stroke (it’s actually similar on all strokes). This means your wrist is going to be submerged about a foot or two.

GPS needs 3 satellites for a proper position acquisition, but really 4 for altitude above the ellipsoid and time. Most modern GPS capture 10-12 satellites in the open.

The frequency, I believe is somewhere between 1.0 and 1.5 GHZ, giving you a wavelength of about 19-25cm. Meaning that you stand a good chance, especially underwater, of losing significant accuracy of your GPS position. This will result in squiggly tracking and incorrect distance tracking - even with a freestyle stroke.

I own a Fenix 3 and experience the same results open water swimming with a freestyle stroke.

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I haven't tried it myself but you could try a swim buoy and place the device in there which would hopefully keep it above water level.

You won't get swimming metrics but you might get the GPS track points OK.

Also, I find that using "Record Every Second" in the Settings >> Data Recording helps accuracy too, for OWS.

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I paddle sprint vessels on the water; so a little more advantageous due to having something to attach the GPS devices. I'm adding an answer because the three devices I use have proven helpful in getting data and perhaps might be helpful to you with just a little adaptation.

Device 1, Garmin Foretrex 410. This is way cheaper than the Fenix but well proven on the battlefield. I once dropped in the water (3ft) after a paddling session & didn't know until I found it again two days later upon returning to the river. It continued to work without any issues! I use this for speed & distance feedback while paddling. Kind of real-time feedback. Yes, there is a lag but you get to know what it is and it works to give you a very good sense of your current status. It is very helpful during sprint pieces to allow you to see exactly where you peak. It is responsive and reasonably accurate.

Device 2, Garmin Forerunner 235. I use this on my wrist mainly for tracking heart rates for intervals and for tracking data to review later. It also has audible cues for intervals. This device is also older & cheaper, but very useful for both real-time heart rate & for reviewing workout graphs.

Device 3, smartphone. For interval audible cues & tracking apps to review after the session. I put the phone in a tight-fitting waterproof pouch with a floater. Always add some floater to your valuable, regardless if they're waterproof. They'd be useless lost on the bottom of the water.

These three devices, plus a camera, have helped me train well with sufficient data for (almost) real-time, and for later review. I've been using them for many years (the Forerunner watch is more recent but the Foretrex 410 has been with me for 6-7 years, with the 301 before it, adding to nearly a decade of good use).

How to apply to your case:

Suggestion 1. Get an elastic strap from any fabric store the same size as the wrist band and loop on the watch to wear across either your back near shoulders or the back of your head. Since you swim head out of the water, this might work, or

Suggestion 2. Wear a cap that has a bill (a baseball type cap). Maybe even get one with a clear visor/bill. You can attach your watch to the bill via some simple configuration. You can even cut two openings on the bill just far enough apart to loop the watch band around the middle of the bill that will allow you to see its face & data. Attach the band through the slid-openings & voilà, you've got a working solution. Be careful as the cap can sink fast if you hit a wave or the wind blows it far from your reach. I've lost a few through the years in rough water or wind conditions. My solution is add something to help it float. It doesn't need much, even a fishing bobber will keep it dangling near the surface. Of course, test it out first.

Suggestion 3. Secure it to a small flat piece of wood or foam with a string and drag it behind you. It's a little awkward but I believe still better than changing your stroke techniques.

Hope one of these can be helpful for you. Enjoy!

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