Patented a few years ago by Hobie!

The fins reverse for reversing propulsion and fold up/back on impact to reduce damage when striking underwater obstructions. Read the full abstract. I can't tell if the socket might be similar if not the same.

It appears there is a short lever at the base of the drive that you lift or pull to reverse thrust.

I don't really find myself wishing I had a reverse often, but it would be nice to totally stash the paddle for emergencies ..
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