Conclusion:
It is hard to measure the friction for each ski pair in each run, but
since the velocity did not increase after the skier passed 5m, the
speed was constant between meter 5 and 30.
Also,
all the measurements have some errors. The actual speed is pretty
accurate, measured with a photogate timer, though there might be
slightly different air resistance in the different runs. The hill was
probably not exactely constanst angeled either.
The skies where
numbered in order that 100 had the most coarse structure while 103 had
a very fine structure. The results showed that on the wet and warm
conditions, the a coarse strucutre had an advantage compared to the
finer ones. Though the most coarse pair was not the fastest. Maybe it
was not wet enough or simply because 101 is a really good ski pair!
Professional skiers know that and test dozens of skies before every season!