While off loading a sling-load of bales of seaweed the pilot sensed a transient "buzz" from the tail rotor which disappeared with the application of yaw pedal. On the transit back to the pick up point at about 200 feet amsl and 60 knots IAS there was a brief, high frequency, vibration throughout the airframe followed by a loud noise. The helicopter's nose pitched down sharply. A witness on the beach saw the tail rotor separate and fall, apparently intact, to the sea. The pilot was unable to stop the violent rotation but as the helicopter approached the beach he closed the throttle and pulled full collective. The helicopter landed on some rocks and rolled on to its side. The pilot who was wearing a safety helmet and a full harness was shaken but uninjured.
