Although I do like Scott's answer (which would almost be as much fun as watching a 42' 5ver get in a slot in the 200 loop)
Here is the official version:
The trailer has both upper and lower decks. The upper deck has a concealed hydraulic lowering system that smoothly brings the upper deck down to be recessed into the lower deck where it can be loaded. A boat or several personal water craft can then be floated on. With an optional insert, a small car, golf cart or several ATV's can be driven onto it. Then it is hydraulically raised to the traveling position.