@igkya - since the boat speed and path are 'constant', I believe it does represent real case scenario...at least close enough to prove a concept. Look at the animation Hortonism has on the right side of this page. Since it simulates a moving boat and skier, if you froze or took a snapshot, does it not still accurately represent a path example? Look at an animation of sine wave generated by a rotating unit circle.
There has been much debate over whether the pendulum example is valid, because of such factors as...skier is not a steel ball (or whatever), the boat is moving, the wind, etc etc, blah blah.
I contend the force (vector) generated by the moving boat (and translated to the line) is analogous to the force (vector) of gravity acting on a swinging pendulum.