I used runtastic, it showed max velo of 13.4 km/h. At 1.7-1.8kW. We drove around over an hour with a standup paddle windsurfboard and the Boosted board. We tried some towing also, it was hard to hold the rope.
Its a little bit strange: If i take the pitch of the prop and the RPM, the props velocity without slip is around 30km/h. The inlet diameter of the duct is 160mm, reducing to 140mm at the outlet which is a factor of 1.3. Divide 30 by 1.3 is 23km/h. 13/23=57%, so the slip is higher than expected.
I could not mount the old drive system, because i was not able to open the nut of the cable plug by hand, so i was not able to test it to compare directly.
Any suggestions how to proceed? Higher pitch? Higher Kv? Vanes?