I’m riding ductless with 3d-print props so far. They aren’t the most effective but all edges are dull. I guess the same cut wouldn’t be possible with rounded nylon.
that prop edge looks inherently dangerous duct so 
that your cut knee wasn’t worse!
Wow! Glad to hear nothing serious happened! I ride without a fail safe leash and only rely on remote, accelormeter and my own reaction to let go the throttle! VESC takes couple of milliseconds to respond for no pwm, plus accelormeter algorithm only runs at 100 hertz, add to this bluetooth latency of max 15ms all these delays makes me very uncomfortable! at the other nad leash by itself can introduce new danger, like getting tangled to prop or other stuff!
Wow… good to hear you are fine.
Propeller safety vs efficiwncy is my main concern in developing my efoil for rental business.
My idea is to go with multiple ultrasonic sensors and capability of motor to stop fast enough (either with breaks or with “steper” feature) whenever motor does not get “positive”/“clear” ping from multiple sensors procesor.
This would open possibility to have ductless prop, maximize efficiency without compromizing safety.
Or you could simply use a magnetic switch that cuts the motor power from the ESC before the rider touches water