I use what I call the 3:00 technique. Basically, imagine the island as a clock, take note of where the 50 rupee spot is when you go through the last ring, and aim for the area three hours behind where the 50 rupee spot was.
Example: you get through all the rings, and upon getting he last ring, the 50 rupee space is in the 6:00 position (bottom of the wheel) aim one quarter of the clock behind that spot, at the 3:00 spot (right side of the wheel). This takes lots of practice, patience, and a well controlled temper, because you will probably end up hitting one of the ripple spots a few times as they are right next to the 50 spot.