I’ve noticed this tends to occur for me as well, I think the watch temporarily loses gps when it goes underwater and this can lead to a spike in speed because the position jumps quickly once it gains signal again. If you look at the speed graph its usually accompanied by a very short spike in speed for these types of events.
I think top speed averaged over 30sec to min would be a much more reliable metric. I like the trend in downwinding to go by average over a km for this reason
From what I understand. KT did it and then said, well the normal human can’t do what Kane can do, so let’s revise those top #'s down a little bit. 
Prone on Lift 150x I usually get 15-17kts but the other day I hit 19
I’ve noticed that i have a hard time going much faster than the wind. My current thinking is that a rough upper limit is about 1.4 times the windspeed which seems to line up with my experience. My reasoning being that a wing can’t go upwind any better than maybe 45 degrees off the wind which i think comes out to 1.4 times faster than the wind when going downwind at optimal apparent wind. I’d be happy to be corrected on this though
All any of us can measure reasonably is SOG, so you just have to know if you are somewhere with a current. You could somewhat cancel that out by averaging runs in “opposite” directions, but you wouldn’t actually be 180 apart at your fastest angle. I imagine a wave pushing you along is also going to cause a SOG/STW mismatch.
For my garmin I think you get a data point every second. Recording under the windsurf activity, for each “run” you get average speed, max speed(instant), max speed(2 sec), and max speed(10 sec). It resets to another run when you slow down enough by falling or coming off foil. I use the 2 second one as my “max speed” and it is always higher than the 10 second one. That matches with my experience though, it only feels like I’m maxing the speed out for 3-4 seconds at a time given my ability before I have to back off or wipe out. I ignore the instant max speed.
I imagine the accuracy of the gps device matters too. Watches seem to vary quite a bit, I follow dcrainmaker for reviews and he does very thorough GPS accuracy testing on variables as part of very in depth reviews. He doesn’t test speed specifically, but that’s just derived from the location data. If the GPS data is not consistent the speed certainly won’t be.
If we were trying to confirm records we would probably need a 10hz or higher GPS, but I don’t think anyone is packing that into a wearable. Could have some fun sticking a pitot tube out the front of your foil too. But for me it’s just a comparison against myself. Can I push a little harder for a brief moment, can I hold a higher speed for a longer time, is my average and/or max speed different on a new foil.
It is nice to know roughly where you stand against others on different equipment so even if I won’t read into this as too precise it is an interesting thread. Seems the low 20s are very common amongst those of us not focusing on maximizing speed or using mikes lab haha.
Coros supposedly is using 10 hz gps, but i haven’t been able to verify that. Sailing instruments like the vakaros atlas do. You can see gwen from wing foil pro center using one in some of his youtube videos measuring foil stall speed etc. It’s much larger than a wearable though, so not very practical
That depends on the GPS module. Speed can be determined at much higher accuracy using doppler measurements.
Is there a trick to getting 2s max and 10s max for runs? I’m only seeing “right before you crash max” currently on a garmin epix gen 2 using a copy of windsurfing activity.
The top end of a foil is mainly decided by it’s zero lift drag. As you go faster, for any given rider weight, the angle of attack and the lift coefficient continue to drop, asymptotically approaching zero. By having the induced drag tend to zero, you are left with the zero lift component of drag.
The zero lift component can be broken down into friction and profile (or oressure drag). So, less planar area means less wetted surface means less friction drag. Thinner profiles and less camber mean lower frontal area and thus less pressure drag. Lower aspect ratio means less span so less frontal area and thus less pressure drag.
If you look at the above list, many of the design trends that increase top end reduce bottom end.
This is of course very simplified, in reality the immersed mast, fuse, and stab all add drag that will add up to a significant chunk of the foil zero lift drag, for most normal foil sizes (big pumping foils excluded).
