Open-water swim distance differs from the track recorded? (Todays swimrun 352m vs. approx 750m, unacceptable)

That the software is buggy. I'm pretty sure that was already pointed out.

The fact that it sometimes gives the correct result changes nothing about this. A broken clock is right etc etc.

@JeyJey is right. If it was a major software error then it would not work for anybody. My 955 works very well in openwater swimming and the distances I measure before my swims match very closely with what I see after I have swum. I couldn't be happier with it. Even better, my pool swims show perfect distances every time. 

If it is down to software then it must have something to do with the stroke style or stroke analysis (swimming with paddles could be messing with that, who knows?). What I see when comparing mine to these faulty swims above is that there are a lot of dropouts in the pace charts, which could also point to GPS acquisition problems. My swims don't have nearly as many dropouts and before every swim I start a OWS activity while I'm getting ready. Then I discard it and start the real activity.

Software errors don't need to affect 100% users. That's just weird. Is your acute load stuck and all the related stuff like training status, daily suggestions, race predictions and what else? Mine is. So it's not software error as your watch isn't stuck? That makes like 0 sense.

Amount of dropouts seems to me somewhat key and handling of those. If less dropouts the weird handling doesn't affect you so much as with the people having more dropouts. The dropouts could be HW issue, but I still highly doubt that as there's like no real indication it being HW issue rather than issue how the dropouts are handled. Amount of dropouts can maybe also have some tweaking on SW side in the GPS chipset firmware.

Also again the 945 case, issue could be fixed by software.

My acute load and Training Status/Readiness are not stuck and get updated according to my workouts as expected. Those and HRV are the only things I really focus on and seem to work consistently. The daily suggestions I ignore because I have my own plans. Same with race predictions, it's too much of a gimmick for me to obsess over. 

unixcrab said:

If it was a major software error then it would not work for anybody.

Eh, no, that's not how bugs work. You can go from 100% working to completely broken by just small nuances, which might be as simple and seemingly irrelevant as whatever the previous activity was. (For example, if the watch state doesn't properly reset all internal state)

That's not a random example: it's a major bug with Connect IQ right now on FR955.

unixcrab said:

Even better, my pool swims show perfect distances every time. 

I have no idea why you even bring this up as that is a completely different measurement method. It doesn't use GPS (doesn't work indoors!), but uses the accelerometers on the watch to find direction changes and multiplies them by the pool size you configured. There isn't even any track to have inconsistent distances off.

The methodology couldn't be more disconnected from what's needed to measure open water swim distance!

I owned many Garmin watches, and from Fenix 6, 945, Fenix 7 and 955, OWS became just unusable. If i switch to my old 920XT or a Suunto 9, i haven't any kind of problem.

I don't know what's wrong with your watch, or anybody else here, and any claims in this forum about HW or SW are pure speculation until Garmin actually finds and fixes the fault. There's no doubt that there is a problem somewhere but we're all stabbing in the dark. I'm just giving my experience as input to provide some context. If you've RMA'd the watch and it's still not working then holding out for a software fix any time soon is probably wishful thinking if some of the other comments here are anything to go by.

Of course they are pure speculation but that doesn't make the thing like one just can't know or something wouldn't be more probable than other.

For starters, even some "HW" bugs can be in the software, the firmware running the HW. SW bugs are just just more more common than HW bugs and even if there is HW bugs there are usually possibility to do some workaround or other solutions to avoid the HW problem with SW. Also the HW can be just some FPGA that can be fixed with "software". SDR are also pretty common nowadays.

I'm fairly competent that Garmin can fix this (or do a workaround) in SW if they want to and admit the problem. Harder thing is to get Garmin to admit that there's a problem and to investigate it. They have their hands full on a lot of other bugs already.

And you are giving your experience, what experience do you have on the subject of coding, embedded devices, firmware, software etc? Or could we just focus on the issue.

I am having the same issue with my new 955 :(. 735XT has always been great/ accurate for recording, now my average pace has increased about 40+ seconds if i go by the distance logged on my last two swims!! 

I did a comparison with the GPX file & Garmin but they both said the same distance, however, if i look at the pace graph it shows clear points where it has dropped the signal (im assuming) and the pace drops off a cliff with it.  Garmin also thinks i stopped for more than 2 minutes during the swim when in fact I swam straight through.   

Previous two comparable swims, as today's was a lot shorter:  

955 - 1hr 44 min, 4010yds, 2:36 / 100yd pace

735 - 1hr 40 min, 4511 yds, 2:12 / 100yd pace

Have my first ironman in 10 days, bought the 955 specifically so it would last the length of the race so not best pleased about how inaccurate it is!

Attached pic from today's pace graph to illustrate.