Today was good weather after a week of rain. Finally I could test my drive on the lake for the first time.
My conclusion is that it is worthwhile for me to invest further (e.g. waterproof electronic box, waterproof remote, mounting on the windsurf board, optimizing the impeller and nozzle)
With the standup board and drive in my hand I reached a speed of 8km/h, current consumption was about 60A with 6S Lipo. Throttle was at about 75%. More I could not give, since I could not hold the drive with one hand otherwise.
I also had the problem that I always created a vortex in the intake area which sucked in air and lost thrust.
My next test will be with my Windusrf board, which probably has better gliding characteristics than the StandUp board.