I was attending a boat show last week and saw a video of a new boat toy.
It was a tube type device, larger than a full size rear tractor tire, that was covered in nylon on the bottom. In the video, you see the tube being pulled by a boat, getting up to speed, with a rider in the tube device.
When the tube gets to maybe 25, the rider braces his feet on the rear side, grabs a rope at the front of the tube, and stands up quickly, pulling back on the front of the tube.
Obviously, the tow rope is attached like you would attach a string to a kite--mid way on the "kite".
At that speed, it is like an airfoil, and the tube/rider take off! He "steered" it by leaning left/right. I don't think he could control the climb or decent, so that would be the realm of the boat driver.
Looked terribly UNSAFE to me.
Ron