Like most KISS installatons, i have a line from the lower end of the vane that keeps the windmill head to wind, down to the pole (to preven it doing 360's endlessly)

I can reach up an catch the lower loop you see in the photo
I run a line from it to the radar support and tie it off at the appropriate length to hold the blades at a suitable angle to the wind. (say 30 degrees to lower outpuot, or 90 degrees to stopo it). Sometimes I leave the line there, with the bottom tied off so it canot fly up into the blades.

In practice, with the boat swinging around, the blades vary from very fast to quite slow every 20 - 60 seconds. Current generated swings widely too, but this is OK, since the average current is too low to overheat the windings.

I would not want to poke a boathook up there when the blades are turning.