50cm deep, off the top of my head.
I carried a GPS for this session with a kite, then dowloaded to a software program to rationalise the track data to these stats:
5 bests' average = 68.93km/h [37.22Knots]
Best Speed n?1 = 71.31km/h [38.51Knots] (39.6 meters in 2.0 sec.)
Best Speed n?2 = 69.36km/h [37.45Knots] (38.5 meters in 2.0 sec.)
Best Speed n?3 = 69.36km/h [37.45Knots] (38.5 meters in 2.0 sec.)
Best Speed n?4 = 67.78km/h [36.6Knots] (37.7 meters in 2.0 sec.)
Best Speed n?5 = 66.83km/h [36.09Knots] (37.1 meters in 2.0 sec.)
Best Speed n?6 = 66.83km/h [36.09Knots] (37.1 meters in 2.0 sec.)
Best Speed n?7 = 66.14km/h [35.71Knots] (36.7 meters in 2.0 sec.)
Best Speed n?8 = 66.14km/h [35.71Knots] (36.7 meters in 2.0 sec.)
Best Speed n?9 = 65.58km/h [35.41Knots] (36.4 meters in 2.0 sec.)
Best Speed n?10 = 65.54km/h [35.39Knots] (36.4 meters in 2.0 sec.)
5 best 100 meter (at least) average = 65.26km/h [35.24Knots]
100 meter run n?1 = 69.17km/h [37.35Knots] (115.3 m. in 6.0 s.)
100 meter run n?2 = 66.92km/h [36.13Knots] (111.5 m. in 6.0 s.)
100 meter run n?3 = 63.98km/h [34.54Knots] (106.6 m. in 6.0 s.)
100 meter run n?4 = 63.69km/h [34.39Knots] (106.2 m. in 6.0 s.)
100 meter run n?5 = 62.57km/h [33.78Knots] (104.3 m. in 6.0 s.)
5 best 200 meter (at least) average = 62.26km/h [33.62Knots]
200 meter run n?1 = 65.45km/h [35.34Knots] (218.2 m. in 12.0 s.)
200 meter run n?2 = 65.2km/h [35.21Knots] (217.3 m. in 12.0 s.)
200 meter run n?3 = 61.77km/h [33.35Knots] (205.9 m. in 12.0 s.)
200 meter run n?4 = 60.99km/h [32.93Knots] (203.3 m. in 12.0 s.)
200 meter run n?5 = 57.9km/h [31.26Knots] (225.2 m. in 14.0 s.)
5 best 5 second (at least) average = 65.26km/h [35.24Knots]
5 second run n?1 = 69.17km/h [37.35Knots] (115.3 m. in 6.0 s.)
5 second run n?2 = 66.92km/h [36.13Knots] (111.5 m. in 6.0 s.)
5 second run n?3 = 63.98km/h [34.54Knots] (106.6 m. in 6.0 s.)
5 second run n?4 = 63.69km/h [34.39Knots] (106.2 m. in 6.0 s.)
5 second run n?5 = 62.57km/h [33.78Knots] (104.3 m. in 6.0 s.)
5 best 10 second (at least) average = 63.29km/h [34.17Knots]
10 second run n?1 = 67.04km/h [36.2Knots] (186.2 m. in 10.0 s.)
10 second run n?2 = 66.03km/h [35.65Knots] (183.4 m. in 10.0 s.)
10 second run n?3 = 61.7km/h [33.32Knots] (171.4 m. in 10.0 s.)
10 second run n?4 = 61.53km/h [33.23Knots] (170.9 m. in 10.0 s.)
10 second run n?5 = 60.15km/h [32.48Knots] (167.1 m. in 10.0 s.)
I wasn't using a speed specific board though. The max speed readout on the GPS showed up as 41.7kts that day, but you can't really trust it so much. The inaccuracy in the small cheap GPS antennas occasionally puts your location off by several metres, and the inbuilt doppler correction function doesn't really help cancel out the spikes on the readout that much.
From another day:
and Olaf Marting going for it in the Speed Week in Namibia (same place where I recorded the above):