On June 14, 2012, at 1637 eastern daylight time, a Robinson R22 Mariner, N1089N, registered to Watercraft Photo Helicopter LLC, collided with the Atlantic Ocean about 10 yards off shore while practicing a simulated autorotation in the vicinity of Oak Island, North Carolina. The helicopter sustained substantial damage. Visual meteorological condition prevailed and no flight plan was filed. The helicopter was operating as a 14 Code of Federal Regulations Part 91 personal flight. The private pilot and commercial pilot passenger reported no injuries. The flight originated from Wilmington, North Carolina at 1630. The pilot stated she was in cruise flight at 600 feet mean sea level at 75 knots, when she entered an autorotation over the ocean, with an intention of a power recovery. She lowered the collective pitch to the full down position and rolled the throttle to the full off position. She then raised the collective pitch. The main rotor rpm started to decrease and the low main rotor audio sounded. She rolled on the throttle and increased collective and the main rotor rpm continued to decrease. The helicopter continued to descend until it impacted the ocean and rolled over inverted. The pilot rated passenger stated when the pilot informed him that she wanted to do an autorotation, replied that he did not feel comfortable with because he did not have that many hours in the left seat. In addition, he was not sure if they could do an autorotation without an instructor pilot on board the helicopter. When asked if there was anything mechanically wrong with the helicopter, before the pilot initiated the autorotation, the passenger stated no, "It was an improper use of flight controls." Examination of the helicopter revealed one main rotor blade was damaged. The cabin floor, sidewall structure, and center console had separated from the main structure just forward of the forward cabin seats. The bottom of the fuselage was buckled. The left rear skid mount was separated and the skid assembly was displaced forward. The tailboom assembly was buckled on the lower left side at its attachment point. There was evidence of a main rotor blade strike on the tailboom assembly. The R22 Maneuver Guide, STRAIGHT-IN AUTOROTATION WITH POWER RECOVERY states, " 1. The Entry - From level flight at 70 to 75 kts, 500 to 700 feet AGL, and headed into the wind, smoothly, but firmly, lower the collective full down without reducing the throttle. Coordinate the collective movement with right pedal; for trim and aft cyclic to maintain a 75 kt attitude....2. The Glide - After descent has been established, slowly reduce the airspeed to 60 to 70 kts and maintain this attitude throughout the glide....NOTE As the aircraft descends through 100 feet AGL, make an immediate power recovery if the following conditions do not exists: 1. Rotor rpm in the green. 2. Airspeed 60 to 70 kts. 3. Rate of descent less than 1500 feet. 3. The Flare - At approximately 40 feet AGL, begin the flare with aft cyclic to reduce forward airspeed and decrease the rate of descent....4. The Power Recovery - At approximately 8 to 10 feet skid height, begin to level the helicopter with forward cyclic."