In general it is fairly dangerous to land a helicopter on a ship. As you can tell when you are onboard, the ship (read: landing pad) moves around making a safe landing very difficult. In fact you may notice that on most military ships with a helicopter pad theyll actually use a winch to pull the helicopter down to the ship. Obviously not many civilian ships have the such equipment.
Therefore on nearly all helicopter/shipboard rescues, the Coast Guard will drop either a basket or a tether to move people onto and off a ship at sea.