The pilot said he thought that the approach to the helipad seemed and felt normal, but in retrospect was flat. A witness on a passing ship thought that the approach was flat and fast. He indicated that the helicopter was in a nose high attitude when the tail rotor hit the ground between rocks at the waterline and the edge of the pad. The pilot felt a jolt followed by a shutter. Because of the tail rotor damage, the helicopter yawed out of control to the left. It rotated 360 degrees as the pilot lowered the collective. Once completely on the ground, he pulled the fuel flow control lever (FFC) out of the flight gate, pulled the emergency fuel shutoff control, and powered everything down while applying the main rotor brake.