Hi @SnappingT , if you see my first post, I asked what we thought the root cause of times being above 50min. Was it a course set too long or was it current. These are two separate factors, although they can result in slow times in combination. I am not asking to normalize for current which is impossible, but if the course is long and we CAN determine the actual distance with enough data points, then we can calculate average paces and thus time over 3800m.
In terms of the accuracy of gps, technically you only need a GPS reading (coordinates) at the start and each turn buoy nd then at finish from the majority of watches. What happens in between is irrelevant in terms of measuring a course over the water.
In my last 6 half IM’s my Garmin 735 has given me distances of 1900m plus 20-30m and that may just be the line that I swam.
While there commercial GPS is not military grade for a precision reasons, its still pretty darn good. A watch going under water literally does not change anything as it is above water half the time and the location where the watch goes in and comes out is picked up. For most swimmers the watch exits the water behind where it goes in (most of us have slip), and the GPS software measures that and corrects for it (otherwise the track would be watch going forward and backwards constantly.
A combination of GPS coordinates (forwards and backwards on each stroke) and accelerometer reading gives enough data to get the precision correct frome what I understand.
Most of the inaccuracies is swimmers swimming longer than the set course. But measuring the set course can be done with decent precision. The set course itself may be wrong relative to the advertized distance (which was what I was trying to get a grasp on in my inital post). Does that make sense?
Course was long due to starting on the beach side of the pier. I had 4450, and many folks had 4500+. I didn’t talk with anyone under 4300. Also, siting was a bit hard. Take 500 m off and my time was spot in
Hey David, nice job out there swimming the looong course!! We have several up thread here at 4020/4040/4047/4050/and a 4119 from some of the faster swimmers, so looks like a bit over 200 meters long maybe…I just watched some video of the start and for sure you got a little over a 100m starting from the beach, then almost that much more taking that left turn to get on the actual course, so that makes sense with all those low 4k swims coming in on the watches…
SO for the other longer catches, well most likely people going way off course. But as SnappingT says, it is placing vs the other folks you measure yourself against that is most important. But for those that only compare themselves against themselves, you can add in a couple 100 meters for a scratch course I would say, and the fast guys that swim straight usually bore that handicap out pretty much…
So circling back to this swim, I think you may have gotten the true distance of the test swim most correct. It looks like for the pros that swim was about 3/3 1/2 minutes long factoring in variables, so roughly 250 to 300 meters long from the actual race course.
Curious as to what some of you got on race day that swam relatively straight??
Spoke to Sam Askey yesterday and he said it felt long, and said Saturday’s race also felt long - his 10k ows pace is 1:08/100m and it was 1:11 race day. I’m impressed!
He asked to discuss changes for his 2025 bike fit and invited him to chat over an ocean swim, but after seven jelly fish stings during the race, including to his face, he passed and opted for an ocean view from ashore. Wurf has really supported him, which is awesome. Skipper pinged me last month to send him a saddle and was a good call.
I would guess that the race day swim was pretty much spot on within a few meters. I dont know how you feel a few meters in a swim that long. He certainly should have had a pretty clear open course, and his time as compared to the pros and historically was very fast.
But to me it is still Lars Jorgensen who has the overall record, or you could say the old long course record and now Sam has the new shorter course one…And it could be that his 1;08 pace is in an actual OW race with others, and that would make sense in comparisons…
Dude set a new swim course record on race day of 45:43 and a finish time of 9:26, pretty legit! I was standing on the pier at the start line and he was the first age grouper to swim by and I was like wow he is moving better than the pros!
3,856 meters on race day, versus 3,862 meters nominal. So the course was pretty close to spot on. There was a strong, inward current at the turn across the top of the course, so maybe compressed it a few meters?
