I remember seeing an event on Chautauqua Lake, New York State between the Chautaqua Belle steam paddle wheeler - 100ft+ length and a stupid jetski/personal watercraft.
The jetski stalled 20-30 feet right in front of the path of the Belle. I think the Belle goes about 6knots or so. There was really no way the Belle could avoid a collision by turning or reversing.
I forget how it ended - I think the jerk got his damned contraption out of the way at the last moment.
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One of my sisters gave a rough analogy that I think although not completely true gives some insight into why some people shouldn't operate boats or airplanes:
Driving a Car is 1-Dimensional. (think roads - you are most of the time following a line - largely you have to watch out for what's in front of you and behind you on that line)
Driving a Boat is 2-Dimensional. (you are on a 2D plane, you have to look all around on your plane which is the water you are floating on to get the full picture)
Driving a Aircraft is 3-Dimensional. (you are in a 3D space - and you should be aware of things in every direction)
Not that we all don't know at least several people personally that we think shouldn't be driving a car.
-CB