GPS Notes

A couple of years ago I picked up a Garmin 310xt GPS watch to use to track my open water swims. A few fellow Southenders used other Garmin watches either in a Ziploc bag or just stuffed under their caps, but the 310xt was the first properly water resistant GPS watch that Garmin had made and liked the reassurance that that capability gave me.

Because GPS receivers perform poorly or not at all while submerged, the first thing I did with the 310xt was take the strap off and attach it to my goggles using some upgraded spring bars that I had lying around (the 310xt had notoriously flimsy spring bars). You can see the 310xt on the back of my goggles in the header photo for this site – the 2011 Trans Tahoe was one of the first times I used it.

GPS Goggles!

GPS Goggles!

This was a little bit of a pain to do as the gap between the spring bar and the watch is barely large enough for the rubber strap of the goggle to fit through. Probably a better method would be to attach some Velcro straps and use those attach the unit to the goggle strap.

I have a tendency to replace my open water goggles fairly frequently as after a number of swims I have a hard time getting my left eye socket to seal properly. Having to fiddle with the spring bars to break out a new pair of goggles was not going to work for me so I ended up switching to just shoving GPS unit under my swim cap. This has one downside in that it is easy to drop the unit when taking your cap off, especially if you are cold and forget it is in there.

The 310xt does have a firmware update that enabled it to correct somewhat for the lack of consistent GPS signal while worn on the wrist, however I never tried it since I had already removed the straps by the time it came out.

My minimum swim when down at Aquatic Park is a counter clockwise circuit of the cove, first out to the buoy at the entrance, hug the pier down to the “goal posts”, head to the flag buoy and then back to the club along the buoy line. This route is in the picture below:

310xt in Cap

The track was recorded with my 310xt stuffed under my cap and records a 0.85 mile round trip which is pretty close to the average of my single cove swims of 0.86 miles.

About a month ago my 310xt stopped functioning, so I looked at getting a replacement. 310xt’s are going for ~$200 online these days, but none were available locally and I was a little impatient so picked up a 910xt for basically twice the price (though I was able to get a $50 rebate for my non functioning 310xt due to a promotion). I am not the most frugal fellow when it comes to gadget purchases.

The 910XT has a much improved screw pin system for the wrist strap attachment, but it did mean that I wasn’t easily immediately able to de-strap it and shove it under my cap (though possibly with some scrounging I might have been able to improvise the required screwdrivers). Instead I decided to order the Velcro strap kit which comes with the appropriate tools, and had the idea that that strap might work under the swim cap.

While waiting for the strap kit to show up I gave the 910xt a whirl in the bay on my wrist. It has a similar correction mode for open water swimming as the 310xt and I was curious to see how accurate it was. The below picture is using the 910XT on my wrist and doing a single cove

910xt on Wrist

The recorded distance was 0.95 miles which is a little over 10% longer than my standard single cove swim, and much to what I had been led to expect from the write up on the excellent DC Rainmaker review. There is definitely some advantages to wearing the 910XT on the wrist – no worries about it falling out of your swim cap for a start, and it was nice to get my stroke cadence data from the built in accelerometers (56 strokes per minute). Overall though I think I have a little bit of OCD about wanting the distance to be accurate so was keen to get back to the under the cap method.

The Velcro strap kit is pretty easy to install though I did end up destroying one of the original screw pins getting it out. It should be noted that the strap is not very long – anyone with 7+ inch wrist circumference might be challenged to use it. The kit adds a small plastic loop to the watch that extends the overall depth/curvature of the watch head making it slightly harder to easily store under your swim cap (It’s not quite as bad as in the photo but I was too lazy to re-attach for the photograph).


This was a bit of a pity as it would have been nice to have an easy option to use the 910XT in either mode – especially since the 910XT could be used a replacement for my Garmin Swim, reducing the gear I take when I travel. I’m contemplating getting the Quick Release kit as well, to see if that works as a viable solution (i.e. the QR plate doesn’t add too much height to the watch to prevent it easily being stored under the swim cap).

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